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THE JOINT ROLE OF PRATYLENCHUS PENETRANS
AND ASSOCIATED ABIOTIC AND BIOTIC STRESS FACTORS
ON THE ONTOGENY OF SOLANUM TUBEROSUM

BY

Joseph W. Noling

A Thesis

Submitted to
Michigan State University
in partial fulfillment of the requirements

for the degree of
MASTER OF SCIENCE

Department of Entomology

ABSTRACT

THE JOINT ROLE OF PRA'IYLENCHUS PENETRANS
AND ASSOCIATED ABIOTIC AND BIOTIC STRESS FACTORS
ON THE ONTOGENY OF SOLANUM TUBEROSUM
BY
Joseph W. Noling

The interaction between a migratory root parasitic nematode
(Pratylenchus penetrans , a defoliating insect (Leptinotarsa decemlineata), and

their host (Solanum tuberosum) were evaluated under varying pesticide and

 

fertilization regimes. The objective was to study the plant, its pests and
nutrient requirements as a system so as to define levels of plant response
occurring during the growth and development of the plant.

The importance of E. Benetrans, L. decemlineata and fertilizers associ-
ated with S. tuberosum was identified using two analytical techniques, Analysis
of Variance and Path Coefficient Analysis. E. penetrans' most important affect
on S. tuberosum occurred during the tuber initiation phase, reducing tuber set.
Control of E. Eenetrans increased tuber set and then nitrogen (N), phosphorus
(P), or I___. decemlineata limited yield. With an increase in N or P, small tubers
increased in size. The most important influence of E. decemlineata occurred
during the tuber bulking phase, with late-season defoliation reducing tuber size.

Defoliation of S. tuberosum by L. decemlineata reduced population
densities of E. penetrans by influencing the size and possible nutritional quality

of the root system.

ACKNOWLEDGMENT

A wise woman once wrote:

I am but the product of my environment. They have come from many

sides, but all have shared in the creation of the person that is me.

Time cannot. wash it away.

I, too, am a product of my environment. Many different people have
contributed to my development as a person and as a scientist. In this regard, I
would like to extend my sincere appreciation and respect to Dr. George Bird for
his guidmce md support. His ambition and enthusiasm has inspired me to reach
for continually higher personal goals. I would also like to extend a very special
thanks to Thomas Ellis and Dr. Bill Ravlin for not only providing the opportuni-
ties in Entomology but also for the many good times that we shared.

I am also grateful to the nematology group, Dr. Alma Elliot, Jim Kotcon,
An MacGuidwin, Ed Caswell and Lindy Rose for providing the group
camaraderie and the many thoughtful and challenging discussions.

Special thanks are also due to Dr. Emmett Lampert, Ray Carruthers, Ken
Dimoff and Dan Lawson for their technical assistance, especially for the many
thoughtful suggestions that went into the statistical analysis and interpretation
of this data.

To Drs. Jim Bath, Dean Haynes, Ed Grafius and Maury Vitosh, I would like
to extend my appreciation for serving on my guidance committee and reviewing
this manuscript. To all the members of the Entomology staff, thank you for

providing the facilities and the professional climate and atmosphere for

ii

graduate research.

I am especially grateful to John Davenport and Dick Kitchen for the
assistance they provided throughout my training.

I am also grateful to Bob Collins, Fred Warner, Lori Carris and Jack
Mahoney for their untiring work in the field. I could not have been blessed with
a better crew. I would like to extend my appreciation and gratitude to Ms.
Laura Meal for the many hours of technical assistance that went into the
preparation of this manuscript, and to Ms. Marie Pane for typing it.

And last but certainly not least, to my wife Roxanne I would like to
extend a special thanks, for without her love and moral support, this manuscript

would not have been possible.

iii

TABLE OF CONTENTS

Title: The Joint Role of Pratylenchus penetrans and Associated Abiotic
and Biotic Stress Factors on the Ontogeny of Solanum tuberosum.

 

 

ACKNOWLEDGMENTS ....................... i i
LIST OF TABLES ......................... vii
LIST OF FIGURES ......................... x1
I Introduction ........................ 1
ll. Literature Review ..................... 3
A. Pratylenchus penetrans ................. 3

l . Systematics .................... 3

2. Taxonomy ..................... 4

3. Distribution-Economic Importance .......... 4

4. Biology ...................... 5

5. Movement . . . .I ................. 6

6. Penetration .................... 8

7. Pathogenicity ................... 9

8. Ecology ...................... 13

9. Control ...................... 16

B. Leptinotarsa decemlineata ................ 20

l. Life History .' ........ ' ........... 20

2. Biology ...................... 21

a. Overwintering ................. 21

b. Oviposition .................. 22

Egg Development and Hatching .......... 23

d. Larval Development .............. 23

e. Pupal Development ............... 23

3. Mortality ..................... 24

4. Food Consumption ................. 25

5. Population Dynamics ................ 26

iv

TABLE OF CONTENTS, continued

IV.

 

c. Solanum tuberosum ................... 30
|- Life History .................... 30
2. Environmental Influences .............. 33
0- Temperature .................. 34
b. Light ..................... 34
c. Water ..................... 35
3. Plant Nutrients .............. ‘ ..... 37
a. Nitrogen ................... 37
b. Phosphorus .................. 37
c. Effects on Growth, Development and Yield ..... 39
Role of Soil Nutrients and Nematicides on S. W and
E. metrans ........................ 42
A. Methods and Materials .................. 44
l. Planting Procedure ................. 44
2. Sampling Procedure ................. 44
3- Harvesting Procedure ................ 46
4. Nitrogen ..................... 46
5. Phosphorus .................... 47
8. Results ........................ 48
I. Nitrogen ..................... 48
2. Phosphorus .................... 55
C. Discussion ....................... 67

Role of E. penetrans and L. decemlineata on the growth of S. tuberosum

A.

Methods and Materials ................. 82
l. Caged Environment ................. 82
2. Path Coefficient Analysis .............. 83
3. Solanum tuberosum Agroecosystem .......... 91
Results ........................ 94
I. Caged Environment ................. 94
2. Path Analysis ...... ' ............. 109
3. Solanum tuberosum Agroecosystem .......... 117

 

V

TABLE OF CONTENTS, continued

C. Discussion ....................... 127

D. Summary ....................... 141
V. Literature Cited ...................... 143
VI. Appendix A ........................ 154
VII. Appendix B ........................ 164
Vlll. Appendix C ........................ 168
lX Appendix D ........................ 175

vi

Table I.

Table 2.

Table 3.

Table 4.

Table 5.

Table 6.

Table 7.

Table 8.

Table 9.

Table l0.

Table I I.

Table I2.

Table l3.

LIST OF TABLES

TUBER YIELD - Influence of selected management inputs on soil
populations of _P_. Metrans on S. tuberosum (cv Superior).

SOIL POPULATION - Influence of selected management inputs on
soil populations of E. penetrans on S. tuberosum (cv Superior).

ROOT POPULATION - Influence of selected management inputs or
root populations of E. fletrans on S. tuberosum (cv Superior).

Influence of nitrogen fertilizer and nematicide on average seasonal
root, foliage, tuber and plant fresh weight of S. tuberosum (cv
Superior).

TUBER YIELD - Influence of selected management inputs on the
yield of S. tuberosum (cv Superior).

SPECIFIC GRAVITY - Influence of selected management inputs on
specific gravity of S. tuberosum.

Influence of selected management inputs on soil population densities
of E. penetrans on S. tuberosum (cv Superior).

Influence of selected management inputs on root population
densities of E. penetrans on S. tuberosum (cv Superior).

Influence of phosphorus fertilizer and nematicide on average
seasonal root, foliage, tuber and plant fresh weight of S. tuberosum
(cv Superior).

TUBER YIELD - Influence of selected management inputs on the
tuber yield of S. tuberosum (cv Russet Burbank).

Influence of selected management inputs on soil population densities
of E. penetrans on S. tuberosum (cv Russet Burbank).

Influence of selected management inputs on root population
densities of E. penetrans on S. tuberosum (cv Russet Burbank).

Influence of phosphorus fertilizer and nematicide on average

seasonal root, foliage, tuber and plant fresh weight of S. tuberosum
(cv Russet Burbank).

vii

LIST OF TABLES, continued

Table I4.
Table l5.

Table I 6.

Table I 7.

Table | 8.

Table I 9.

Table 20.

Table 2|.

Table 22.

Table 23.

Table 24.

Table 25.

Table 26.

Table 27.

I979 Insect-nematode potato agroecosystem study treatments.

Influence of three inoculated densities of E. enetrans and three
plant densities of L. decemlineata on leaf dry weight of S.
tuberosum (cv Superior).

Influence of three inoculated densities of P. enetrans and three
plmt densities of l_._. decemlineata on leaf area of _. tuberosum (cv
Superior)

Influence of three inoculated densities of P. enetrans and three
plant densities of L. decemlineata on root dry weight of S.
tuberosum (cv Superior)

Influence of three inoculated densities of P. pen ensetran and three
plant densities of L. decemlineata on plant dry weight of S.
tuberosum (cv Superior)

Influence of three inoculated densities of E. metran sand three
plant densities of L. decemlineata on tuber dry weight of S.
tuberosum (cv Superior).

Influence of three inoculated densities of P. enanetr ans and three
plant densities of L. decemlineata on tuber number per plant of S.
tuberosum (cv Superior).

Influence of three inoculated densities of P. pen enanetr sand three
plant densities of L. decemlineata on stem dry weight of S.
tuberosum (cv Superior).

Influence of three inoculated densities of P. aetran sand three
plant densities of L. decemlineata on stolon dry weight of S.
tuberosum (cv Superior).

Influence of three inoculated densities of _E. etran ans and three
plant densities of L. decemlineata on final tuber yield of S.
tuberosum (cv Superior).

Influence of three plant densities of l_._. decemlineata on soil
population densities of E. penetrans.

 

Influence of three plant densities of E. decemlineata on the root
population density of E. metrans.

Simple correlation coefficients between E.
decemlineata and yield of S. tuberosum.

penetrans and I:

Simple correlation coefficients between P. pen enanetr and E.
decemlineata and yield components of S. tuberosum.

viii

LIST OF TABLES, continued

Table 28.

Table 29.

Table 30.

Table 3|.

Table 32.

Table 33.

Table 34.

Table 35.

Table 36.

Table A I.

Table A2.

Table A3.

Table A4.

Table A5.

Table A6.

Table BI.

Table B2.

Simple correlation coefficients between l_._. decemlineata and E.

wetrans.

Influence of selected mmagement inputs on the final tuber yield of
S. tuberosum (cv Superior).

Influence of selected management inputs on root fresh weight of S.
tuberosum (cv Superior).

Influence of selected management inputs on the number of tubers of
S. tuberosum (cv Superior).

Influence of selected management inputs on foliage fresh weight of
S. tuberosum (cv Superior).

Influence of selected management inputs on tuber fresh weight of S.
tuberosum (cv Superior).

Influence of selected management inputs on plant fresh weight of S.
tuberosum (cv Superior).

Influence of selected management inputs on soil population densities
of E. penetrans on S. tuberosum (cv Superior).

Influence of selected management inputs on root population density
of E. wetrans on S. tuberosum (cv Superior).

Influence of selected management inputs on population density of _P_.
metrans on potatoes (cv Superior).

Influence of selected management inputs on population density of E.
penetrans on potato (cv Superior).

Influence of selected management inputs on the root weight of
potatoes (cv Superior).

Influence of selected management inputs on the foliage weight of
potatoes (cv Superior).

Influence of selected management inputs on the tuber weight of
potatoes (cv Superior).

Influence of three levels of nitrogen and four pesticides on the yield
and size distribution of Superior potatoes (I978).

Influence of selected management inputs on the root weight of
potatoes (cv Superior).

Influence of selected management inputs on tuber weight of
potatoes (cv Superior).

ix

LIST OF TABLES, continued

Table B3.

Table B4.

Table CI.

Table C2.

Table C3.

Table C4.

Table CS.

Table C6.

Table C7.

Table DI.

Table D2.

Table D3.

Table D4.

Table D5.

Table D6.

Table D7.

Influence of selected management inputs on foliage weight of
potatoes (cv Superior).

Influence of selected management inputs on tuber number of
potatoes (cv Superior).

Influence of selected management inputs on foliage weight of

. potatoes (cv Superior).

Influence of selected management inputs on stem weight of potatoes
(cv Superior).

Influence of selected management inputs on tuber number of
potatoes (cv Superior).

Influence of selected management inputs on plant weight of
potatoes (cv Superior).

Influence of selected management inputs on tuber weight of
potatoes (cv Superior).

Influence of selected management inputs on root weight of potatoes
(cv Superior).

Influence of selected management inputs on population density of E.
wetrans on potatoes (cv Superior).

Influence of selected management inputs on foliage weight of
potatoes (cv Russet Burbank).

Influence of selected management inputs on stem weight of potatoes
(cv Russet Burbank).

Influence of selected management inputs on plant weight of
potatoes (cv Russet Burbank).

Influence of selected management inputs on tuber number of
potatoes (cv Russet Burbank).

Influence of selected management inputs on tuber weight of
potatoes (cv Russet Burbank).

Influence of selected management inputs on root weight of potatoes
(cv Russet Burbank).

Influence of selected management inputs on population density of E.
penetrans on potatoes (cv Superior).

Figure I.

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Figure 6.

Figure 7.

Figure 8.

Figure 9.

Figure IO.

Figure I I.

Figure I2.

LIST OF FIGURES

Diagrammatic sketch of a single stem potato plant (after
Workman 919, I979).

Relationships of the main components of potato growth (after
Milthorpe and Moorby, I960).
L = leaf area index, Ep = potential rate of net assimilation

Plot design of the Montcalm Potato Research Farm, Entrican,
Michigan.

Relationship between the number of E. enetrans observed in I0.0
ml post-extraction sample and a correspon ing . ml subsample.

Influence of three rates of nitrogen and two pesticides on the
final yield of S. tuberosum (cv Superior).

Influence of three rates of phosphorus and two pesticides on the
final yield of S. tuberosum (cv Superior).

Influence of three rates of phosphorus and two pesticides on the
final yield of S. tuberosum (cv Russet Burbank).

Influence .of two edaphic pesticides on total (soil 4- root)
populgtion density of E. penetrans on S. tuberosum (cv Superior)
I978 .

Influence of two edaphic pesticides on total (soil + root)
population density of E. penetrans on S. tuberosum (cv Superior)
(I979).

Influence of two edaphic pesticides on the total (soil + root)
population density of E. penet'rans on S. tuberosum (cv Russet
Burbank) (I979).

Relationship between independent and dependent variables and an
unexplained residual factor in determining the outcome of another
variable.

Conceptual diagram illustrating sequential effects of abiotic and
biotic factors on yield components of S. tuberosum.

xi

INTRODUCTION

Solanum tuberosum L. (potato) is a widely cultivated and very significant
food crop of worldwide distribution. Potatoes grown in Michigan are subject to
attack by many pests that affect plant growth, development and yield.
Leptinotarsa decemlineata Say (Colorado potato beetle) and Pratylenchus
penetrans (Cobb) (Filipjev & Schuurmans-Stekhoven I94I) (root-lesion
nematode) are pests of prime importance. They can be dichotomized into foliar
and root feeders.

E. decemlineata feeds by chewing the leaves and terminal growth of S.
tuberosum. If defoliation is severe, the plant will die. In less severe cases, the
development of tuber production is inhibited and final yield is greatly reduced.
E. penetrans is a migratory endoparasite that attacks unsuberized roots and
other underground parts of the plant. Small cortical lesions caused by the
nematode-infected plants are poor absorbers of water and nutrients essential
for normal plant growth. The shoot systems of severely affected plants are
stunted, chlorotic and wilt rapidly. These symptoms are a gradual decline or
lack of plant vigor rather than the rapid, striking changes that occur from
defoliation of potato plants by _l:. decemlineata. The susceptibility to E.
penetrans is variable among potato cultivars.

Plants undergoing nutritional stress do not respond to root and foliar
feeding pests in the same manner as healthy plants. It is well documented that
the growth, development and yield of S. tuberosum can be greatly increased by
the use of fertilizers. Differences in the supply of nitrogen and phosphorus can
have marked effects on the growth of the crop and can produce significant

changes in the yield of the plant. Fertilizers, by affecting growth rates and

plant longevity, can determine when and how much plant material is available

for plant pests such as E. decemlineata and E. penetrans. This also determines

 

the food quality of the plant tissue being consumed by the pest.

Much is known about the impact of specific pests and fertilizers on S.
tuberosum growth, development and yield. Little or nothing is known about the
joint action of defoliators, root parasites and nutrient deficiencies on the
growth and development of S. tuberosum. Correspondingly, little is known
about the effect interacting plant stresses have on the population dynamics of
pests attacking S. tuberosum. Changes mediated through the plant by one
stress factor (e.g., L. decemlineata) may indirectly influence the subsequent
impact of a second stress factor (e.g., E. penetrans). Information about this
interaction is a necessary prerequisite for the description of the current states
of S. tuberosum growing in ecosystems housing multiple stress factors. S.
tuberosum is not grown in a pest-free vacuum. Plants are continually subjected
to a myriad of interacting forces. The abiotic and biotic components of agro-
ecosystems are dynamic, and it is essential that an understanding of the joint
action of foliar-feeding and root-feeding pests be studied in respect to all
components of the system. Under such a variety of conditions, levels of
economic damage cm be defined only by studying the plant, its pests and
nutrient requirements as a system.

The objective of this research is therefore to develop a basic understmd-
ing of the interactions among the migratory root-parasitic nematode (E.
wetrans), the defoliating insect (E. decemlineata) and their host (S.

tuberosum) under varying nitrogen and phosphorus fertilization regimes.

LITERATURE REVIEW

PRATYLENCHUS PENETRANS

Systematics

Root-lesion nematodes were observed first in I865 (Sher & Allen, I953).
It was not until I880, however, that Tylenchus pratensis was described by
deMan (I880). Six species, including Pratylenchus pgnetrans, have been
synonomized with I. pratensis (Sher 8. Allen, I953), and much of the early
information pertaining to deMan's description of I. pratensis should be referred
to as Pratylenchus spp. In I9I7, Cobb (I9I7) described I. penetrans, a parasite
of violet, cotton md potato, from various regions of the U.S.

In I927, Cobb reported _'_I'_. penetrans as a probable synonym of I.
pratensis. Since Cobb's description of I. penetrans, Goodey (I932) and Steiner
(I927) synonomized I. wetrans with I. pratensis. In I936, F ilipjev published
the first generic classification of the Tylenchidae md designated E. pratensis
as the type species of the genus Pratylenchus. This work included a list of five
species of Pratylenchus, with I. fletrans synonomized with E. pratensis. In
I952, Chitwood and Otiefa (I952) constructed a new combination resurrecting
the first generic and species name for E. penetrans. Sher and Allen (I953) and
Loof (I960) have made comprehensive studies of the taxonomy of the genus.
Much of the confusion concerning the taxonomy of root-lesion nematodes was

eliminated by these monographs.

Taxonom

The genus Pratylenchus (F ilipjev, I936) contains more than 40 species.
They are difficult to identify because of morphological similarities. The
principal characters used to differentiate Pratylenchus spp. include labial
morphology, cephalic annulation, shape of the tail, length of the posterior
uterine branch and position of the vulva. Comparison of populations of E.
Egetrans from different geographical locations and type hosts indicate exten-
sive intraspecific morphological variation (Mai 33 _a_l_., I977). Vulva position and

stylet length are the least variable and the most diagnostic characters.

Distribution—Economic Importance

E. penetrans is widely distributed throughout temperate regions of the
world. It is common in Europe, Canada and the northern regions of the U.S.
(Loof, I960). The global distribution of E. penetrans may be related to the
distribution of susceptible host plants or climatic factors (Mountain 8. Patrick,
I959; Norton, I978). Soil type also influences the distribution of E. pe_netrans
(Oostenbrink, I96I; Kable 8. Mai, I9680), being more prevalent and causing
more damage in sandy soils (Townshend, I972; Kable 8. Mai, I968b).

E. penetrans is widely distributed in Michigan (Knierim, I963). It was
recovered from more than half of the fields sampled in two recent surveys
(Bernard 8. Laughlin, I976; Elliot, I980). It is the most frequently encountered
phytopathogenic nematode species in Michigan potato fields (Bernard 8.
Laughlin, I976), and commonly occurs at economically damaging levels. It is
the most economically important plant-parasitic nematode species in the

northeastern U.S. (Mai gt gl_., I977).

Host range studies indicate that more than 350 different plant species are
hosts of E. penetrans (Mai g _a_l., I977). These include many economically
importmt food and fiber crops as well as many weed species. It is a major pest
of fruit (Pitcher g a_l., I960; Mountain 8. Patrick, I959) and vegetable crops
(Dickerson 31 2|” I964; Olthop 8. Potter, I973; Barker 8. Olthop, I976; Hastings
8. Bosher I938), causing extensive losses annually within Michigan (Bird, l9800).
Townshend and Davidson (I960) demonstrated the potential importance of

various weed hosts that serve as reservoirs for this nematode.

gem;

The life cycle of E. aetrans consists of the egg, four larval stages md
adult males and females. Reproduction is by amphixis, requiring both males and
females (Thistlewayte, I970). Females deposit eggs singly in soil or roots.
Hung and Jenkins (I969) and Thistlewayte (I970) studied the processes of
oogenesis and embryogenesis. After fertilization, eggs are deposited at a rate
of 0.8 to |.2 eggs per day (Mamiya, I97I). Hastings (I939) reported that the
largest number of eggs laid by a single female was I6. Christie (I959) found
that the optimum soil temperature for reproduction was 2|.I C. Reproduction
decreased as temperature increased above 2|.I C. Kable md Mai (l9680)
demonstrated that soil moisture also influences reproduction.

First-stage larvae are formed with the completion of embryogenesis,
usually 4 or 5 days following egg deposition. The first molt occurs in the egg.
Second-stage larvae hatch in 8 or 9 days at 25 C (Mamiya, I97I). Hatching
takes place as a result of continued stylet thrusting which mechanically
ruptures the egg and provides an emergence pathway for second-stage larvae.

E. penetrans molt three more times, between intervals of feeding, and become

adult males or females. The life cycle takes 30 to 86 days, depending on

temperature and host. It is shortest at 30 C, although fewer eggs are laid at
this temperature than at 20 C or 24 C (Mamiya, I97 I).

Movement

E. metrans is an obligate parasite of higher plants. It must locate a
suitable host plant and successfully penetrate host tissue to establish a parasitic
relationship. As a soil-borne pathogen, it is dependent on a number of biotic
md abiotic factors that directly influence these processes and nematode
survival. Plant roots and gaseous exudates attract E. penetrans. This results in
directed orientation (Klinger, I972). The attraction of E. penetrans to roots is
complex. It is caused by behavioral responses to different combinations of
factors, including gradients of C02, heat and various other substances associ-
ated with root metabolism.

In laboratory experiments, Klinger (I972) demonstrated that E. fletrans
obtains directional cues by tracking concentration gradients of C02 diffusing
from plant roots or fungi. The response of E. fletrans to temperature
gradients spread over relatively short distances was shown in laboratory
experiments by El-Sherif and Mai (I968). These results indicate that _P_.
penetrans is attracted to heat sources, including the metabolically produced
heat emanating from root tissue and germinating seeds. Directional movement
of E. penetrans is also affected by biochemical substances from plant roots or
associated microorganisms (Chang 8. Rohde, I969; Edmunds 8. Mai, I966;
Lavalle 8. Rohde, I962). Lavalle and Rohde (I962) observed that initial
migration of E. penetrans is significantly greater in the direction of host

seedlings. This happens even when roots were removed from the soil, indicating

that diffusible biochemical substances coming from the roots were responsible
for the attraction. Attraction was also directly related to the linear growth of I
roots, with decreasing attractiveness when root growth was slow or did not
occur. While some biochemical substances attract nematodes, other plant-
produced compounds have a repellent effect. In one case, the repellent activity
was related to phenols commonly found in necrotic tissue inhabited by E.
metrans (Chang and Rohde, I969). Klinger (I972) suggested that within the
temperature range of nematode activity, the combined effect of both chemical
and thermal stimuli was probably more effective in the localization of potential
host plants than the effect of any single stimulus.

Many studies dealing with the influence of environmental factors on _P_.
penetrans indicate that soil moisture, temperature and soil type are important
factors in movement md survival. Differences in movement md survival of E.
penetrans are directly related to soil particle size distribution, moisture
retention, aeration and pore size (Townshend 8. Webber, I97I). Kable and Mai
(I9680) demonstrated how specific soil types, soil moisture and soil temperature
affect the survival and movement in soil and penetration of plant roots by E.
penetrans. Survival and movement in soil decreases with increasing moisture
tension from pF 0.0 (field saturation) to pF 4.2, and increasing soil temperature
from 0 C to 37 C. Differential survival in the various soils may explain why E.
penetrans appears to be more severe a problem in sand and sandy loam than
clay or silt loam soils. Survival is lowest in very dry or very wet soil (Kable 8.
Mai, l9680; Townshend 8. Webber, l97l; Kable 8. Mai, I968b).

Wallace (I964) reported that the movement of nematodes in soils is
dependent on the geometrical relationship between nematode diameter, pore

size and the distribution of water. Townshend and Webber (I97I) showed that

movement by E. fletrans in three water-saturated Ontario soils was
negligible. Movement, however, was maximum when 8-l2% of the total pore
space was occupied by air. Differences in E. wetrans migration is due to

various soil pore sizes.

Penetration

Once a plant root is located, environmental parameters influence root
penetration by E. aetrans. These include host age (Wallace, I964), variety
(Bernard 8. Laughlin, I976; Bird, I977), presence or absence of phenolic
compounds (Chang 8. Rohde, I969), soil temperature (Townshend, I978) and soil
moisture (Townshend, I972; Kable 8. Mai, l968a). Ease of penetration is
influenced by plant species. The life stage of the nematode also influences the
invasion of roots. Most stages of E. penetrans are able to penetrate roots
(Townshend, I972; Oyekan gt_ _a_l., I972; Townshend, I978). The capabilities of
the various stages to invade roots, however, are not the same. Kable md Mai
(l9680) observed that only the fourth-stage juveniles and adult stages
penetrated alfalfa seedlings. Townshend (I978) reported a greater infective
capacity of the females, which penetrated corn roots earlier, faster and over a
wider temperature range than males or larval stages. He suggested that the
larger size of the posterior subventral lobe of the females, which is involved in
feeding md penetration, may account for the females' greater infectivity.

Edaphic factors such as temperature and moisture affect penetration.
Optimum temperature for penetration of corn roots by' _P_. penetrans is 20 C
(Townshend, I972). Females penetrated alfalfa roots at temperatures from 5 to
35 C, with maximum penetration between l0 and 30 C (Townshend, I978). Male

and juvenile stages have a narrower temperature range, l0-30 C, with maximum

penetration at 20 C. Oyekan gt g_l. (I972) observed that all stages of E.

wetrans entered roots of pea, usually requiring a minimum of l2 hours. He
observed that the track left in agar by invading stages was often followed by

other nematodes, providing a pathway to a previous infection court. The impli-
cation is that the superior infectivity of females at wider temperature ranges
may increase the likelihood of survival of the species during adverse
environmental conditions when females are in close proximity to host roots.
Differential penetration by E. metrans occurs when host plants are
grown in different soil types or in the presence of soil microorganisms. Morsink
(I963) found that E. metrans failed to enter roots of potato seedlings under
axenic conditions unless the medium was contaminated with fungi. Townshend
(I972) demonstrated that greater numbers of E. wetrans penetrate roots in
smdy loam soils than in silt or clay loam soils. This may be attributable to
greater nematode movement and greater localization of roots in coarse-
textured soils than in fine-textured soils. Penetration is also determined by a

complex of interacting biotic and abiotic factors.

Pat enicit

Pratylenchus spp. cause the formation of root-lesions, usually on feeder
roots and occasionally on other underground parts of plants such as potato
tubers. These species are primarily parasites of the root cortex, although other
components of the root may be invaded. Primary plant symptoms commonly
associated with high population densities of E. metrans include cortical
necrosis and cellular discoloration of the inner cortex and adjoining endodermal
cells. Secondary symptoms of E. penetrans injury is usually seen in the above

ground part of plants, which are stunted and chlorotic, with early death of older

10

leaves and greatly diminished root systems. Secondary symptoms can, in many

cases, be easily confused with other unrelated non-specific factors such as

nutrient deficiency, and are not always apparent in plants even if infected with
E. wetrans. Plant response to nematode feeding is variable and dependent to
a large degree on severity of nematode infestation, inherent genetic
characteristics of the host and the prevailing environmental conditions.

Feeding by E. Egetrans injures the roots by rupturing and disorganizing
cortex cells. Apple roots react in two distinct ways to invasion by E. penetrans
(Pitcher g 91., I960). First, and soon after penetration, a discoloration in the
invaded epidermal cells occurs. Then, 3 to 4 weeks after feeding on the
cortical cells, a dark streak or lesion can be obseved in the underlying vascular
tissue of the stele. This type of hypersensitive plant reaction to E. penetrans
inhibits the growth md development of the root system, severely infected root
systems generally being greatly diminished with fewer, poorly developed feeder
roots (Taylor gt gl_., I97I). Cellular damage within the cortical tissue also
inhibits the absorption of water and nutrients essential for the development of
healthy plants. Kimpinski (I979) showed that the amount of water moving
through the stems of potato plants infected with E. penetrans is generally less
than in nematode-free plants.

Root lesions form as a result of enzymatic reactions associated with the
plant's response to the mechanical influence of nematode migration (cell wall
damage) and to the substances nematodes introduce into the plant. Plant
reactions to these compounds vary with plant susceptibility. The type and
extent of the injury caused by E. penetrans depends in part on the presence or
absence and relative concentrations of phenolic substances within the plant.

Phenols, in combination with nematode-produced enzymes, give rise to products

11

that are toxic to parasitized and adjacent root cells (Pitcher fl _a_I_., I960). In
both apple and peach roots, the tissues that show the most rapid discoloration in
the presence of E. penetrans are the tissues that contain the highest levels of
phenolic substances. Tuber infections, like root infections, are characterized
by discolored, slightly elevated roundish lesions (Cobb, l9l7). Formation of
root or tuber lesions is not always as prominent as demonstrated in Wisconsin
field studies by Dickerson _e_t_ a_l. ( I964). If infestation of E. penetrans is severe,
lesions may coalesce to form larger areas of necrotic tissue causing a further
overall increase in plant damage (F ilipjev 8. Schuurmans-Stekhoven, l94l).
Roots with dark brown lesions of varying sizes are present on both
primary and secondary roots with the largest lesions usually on the oldest roots
(Filipjev 8. Schuurmans-Stekhoven, I94I). Damage to rhizomes by E. penetrans
is' usually much less extensive than damage to roots. In general, young plants
suffer most from the attacks of E. penetrans (Jaffee 8. Mai, I979). This is due
to the fact that E. pgetrans heavily infects the younger feeder roots of plants
(Taylor e_t a_l., I97I). As the roots age and suberize, the nutritional status of
the root may change and the nematodes migrate into the soil. Age-related

pathological responses have also been observed for PratLlenchus spp. attacking

 

a number of other host plants (Wallace, I973).

The pathogenic effects of _P_. penetrans toward various species of plants
has been extensively studied. Cobb (I9I7) in l9l7 reported damage to potato,
violet and cotton by _E. penetrans. Necrotic lesions on roots and tubers and
reduction in the number of tubers was observed. Hastings and Bosher (I938)
were first to show that E. penetrans, in the absence of other microorganisms,
reduced plant growth 50-75% of seven agriculturally important plants. In

potato pathogenicity studies, Oostenbrink (I954, I958) found that E. penetrans

12

caused a 50% reduction in plant weight and a 20-50% reduction in tuber yield.
Bernard and Laughlin (I976) examined the effects of varying potato cultivars
and initial population densities of E. penetrans on tuber yields. Yield reductions
were related to the tolerance of the plant to nematode colonization rather than
to a specific resistance factor operating in the plant. Wide differences in the
damage caused by E. penetrans to apple trees growing on different rootstocks in
New York was observed by Parker and Mai (I974). Dickerson 91 91. (I964)
showed marked reductions in potato yields associated with high populations of
E. metrans. Oostenbrink (I966) reported a linear relationship between the
initial population densities of E. penetrans and tuber yield. This was confirmed
in I973 by Olthof e_t 91. (I973) and Olthof and Potter (I973). Seinhorst (I950)
reported that the initial population density tolerance limit for E. penetrans at
I I.0 per gram of soil and by Oostenbrink (I966) as 0.4 to I.0 per gram in sandy
soil and 0.7 to 2.0 per gram in loam or organic soil. Olthof and Potter (I973)
(established an economic threshold of 2.0 per gram of soil which was used in
I976 by Barker and Olthof (I976) in a report of nematode tolerance limits for a
number of crops.

The pathogenic relationships between nematodes and hosts varies with
different environmental conditions. Factors that restrict or inhibit plant
growth, such as the cellular damage to feeder roots caused by E. penetrans,
may inhibit growth by reducing the flow of water and nutrients (Kimpinski,
I979). In years with average or below average rainfall, plant growth and yield
losses may be moe severe if high population of E. penetrans interferes with
water and nutrient absorption. These effects may be partially offset by
common irrigation practices, which may provide the plant with adequate water.

Host plants grown in unfavorable conditions, i.e., in soils deficient in potassium,

13

nitrogen or calcium or at low light levels or following defoliation, are more

susceptible and more severely damaged by E. penetrans than vigorous crops

(Dolliver, I96I).

The pathogenic effect of E. penetrans on various host plants may be
enhanced by interacting with other plant pests operating in the soil or on aerial
portions of the plant. Burbee and Bloom (I978) found that an early season
increase in the incidence and severity of Verticillium wilt of potato was
indicative of a nematode-fungal interaction. Morsink and Rich (I968) obtained
similar results, suggesting that root damage by E. fletrans increased the

incidence of Verticillium wilt. Using a split-root technique, Conroy g a_l.

 

(I972) showed that the disease caused by both E. penetrans and Verticillium
albo-atrum was usually more severe as the number of nematodes or level of
fungal inoculum increased. In most studies of nematode-fungal disease
complexes, nematodes increased the severity of fungal diseases. E. wetrans
can cause a breakdown in the resistmce of pea to Fusarium wilt (Oyekan 8.
Mitchell, I97I). It was suggested that E. penetrans induced biochemical or
physiological changes within the plant which were conducive to wilt

development.

Ecolggy

Many factors determine the rate of increase and final density of root md
soil populations of E. penetrans. Studies dealing with the influence of the
environment on population dynamics of nematodes under field conditions show
that soil moisture and temperature are important. Soil type, soil pH, weeds,
cropping history, plant host and chemicals introduced by man (pesticides,

herbicides, fertilizers) all exert some effect on nematode populations.

14

Plant species and the physiological status of the plant have a marked

effect on the subsequent population changes of E. penetrans in the soil and
roots. Dolliver (I96I) showed that changes in population levels of E. wetrans

are related to the degree of stress to which the plant and nematode are
subjected. Populations of E. penetrans in root systems of Wando peas increased
significantly when plants were stressed by defoliation, nutrient deficiencies or
abnormal light intensity. Treatments which severely restricted root growth
significantly reduced numbers of E. penetrans. When plant growth was severely
restricted by early defoliation, root population densities significantly
decreased, but increased when defoliation occurred later. Conditions inhibiting
plant growth cause changes in the physiological processes of the plant, and
influence host plant suitability for nematode colonization and susceptibility of
the plant to nematode injury.

Dickerson g g_l. (I964) demonstrated that population increases of E.
penetrans were influenced by soil temperature, soil type and previous cropping
history. Their results indicate that the optimum temperature for population
increase of E. penetrans varies with the host and did not necessarily coincide
with optimum temperatures required for root or plant growth. Populations of
E. penetrans were shown to increase faster on corn than on potatoes with
greatest population increases at 24 and I6 C, respectively. The study indicated
that crop rotations in Wisconsin, in which corn was growing in rotation with
potatoes, increased the severity of damage caused by E. penetrans to both
hosts. Ferris and Bernard (l96l) reported similar results, with corn and soybean
rotations increasing population levels of E. penetrans. Greenhouse tests by
Wong and Ferris (I968) showed that root populations of E. penetrans increased

more rapidly in potato and peppermint than in onion roots. Bernard and

15

Laughlin (I976) showed in a test of four potato cultivars that up to four times
as many E. wetrans in final harvest populations were produced on susceptible
varieties.

Work by a number of investigators indicates that population levels of E.
penetrans oscillate markedly throughout the year. Many of these studies show
that the seasonal population fluctuations commonly associated with periods of
plant growth follow a characteristic pattern (DiEWardo, l96l; Ferris 8.
Bernard, I96l; Ferris, I967). Based on similar soil volumes, E. p_e_netrans
populations increased in the spring and early summer, before growth of the crop
became extensive, followed by a decrease in soil populations at mid-season
when root growth is usually at a maximum. The mid-season decline is then
followed by a marked increase in soil population densities of E. penetrans during
harvest. Bird (I977) observed that changes in the soil population densities of E.
penetrans may be the result of migration patterns into and out of potato roots
which result in significant changes in root and soil population densities of E.
penetrans during the season. Other causes of population fluctuations may be
due to seasonal changes in soil temperature (Mai g a_l., I977), or soil moisture
(Kable 8. Mai, I9680). Seasonal population fluctuations were observed by
Dickerson 91 a_l. (I964) in Wisconsin potato fields where populations of E.
penetrans increased from spring planting to vine kill and natural root
senescence in August, followed by a decrease in soil populations from
September to February.

Initial soil population densities of E. wetrans are directly related to the
final soil populations from the previous crop and in northern climates to
overwintering survival. Dunn (I972) demonstrated the importance of soil depth

and host roots in overwintering of E. penetrans. Kable and Mai (I968b) showed

16

the importance of soil depth and soil type on overwintering survival of E.

penetrans. Greater numbers of E. @etrans were observed in the top 30 cm of

soil than at lower depths, suggesting that overwintering survival decreased with
increased soil depth. It was speculated that overwintering survival was related
to the permeability of soils to oxygen when water-saturated during the winter
months.

The vertical distribution of nematodes in soil is influenced by many biotic
and abiotic factors. Population size and distribution in the soil is directly
related to the relative size and extensiveness of plant root systems. Wallace
(I964) suggested that distribution of plant roots in the soil is the chief factor
determining the vertical distribution of nematodes, and that physical factors
usually play an important but secondary role. Root distribution, height of water
table, soil moisture, soil temperature and soil texture also greatly affect

vertical distribution.

Control

Plant-parasitic nematodes can be controlled to varying degrees by land
management and cultural control practices. These include exclusion, plant
resistance, various cultural control practices such as following, crop rotation,
cover crops, time of planting, trap and antagonistic crops, field sanitation and
organic amendments. These methods, unlike the rapid efficacy of most
nematicides, tend to reduce nematode population densities gradually through
time. Their primary importance lies in the realm of pest management md
integrated control. Combinations of the exclusion, plant resistance and
population reduction control techniques, coupled with the judicious use of

chemical nematicides, may reduce population levels of nematodes to

17

economically acceptable levels.

Not all land management and cultural control practices are equally
effective in controlling nematodes. For crop rotation to be effective against E.
penetrans, crops unsuitable for growth, reproduction or infectivity must be
introduced into the rotation sequence. E. metrans has a wide host range and
thus limits the number and type of crops which are both feasible and
economically profitable for the grower. With energy and environmental costs
increasing and registration of new materials decreasing, these considerations
may need to be re-examined within a new framework of pest control.

Many agricultural production practices such as introducing inorganic and
organic compounds into the soil have reduced population levels of E. penetrans.
In mmy cases, population reductions following treatment have been due either
to the production of chemical compounds toxic to nematodes or to an increase
in the activity of predaceous microorganisms in the soil (Walker, I969).

More research emphasis has been placed on the influence of nutrients on
nematode reproduction than on the joint influence of nutrients and nematodes
on plant ontogeny. In I96l, Dolliver (I96I) found that moderately reduced NPK
fertilization of Wando peas resulted in increased population densities of E.
penetrans. Nitrogen was reported to have two effects on nematode populations.
Application can result in an increase of nematodes presumably by providing
more feeding sites through stimulation of root growth; however, most reports
indicate that the addition of nitrogen results in lower nematode numbers
(Kimpinski g 31., I976; Patterson 8. Bergeson, I967). It has been suggested that
ammonia was responsible for this phenomenon (Oteifa, I955; Eno 91 9_l_., I955).
Oteifa (I955) speculated that ammonium ions were inhibitory to egg hatching.

Several forms of nitrogen have been studied and not all were equally

18

effective in (their influence on nematode populations. Walker (I97l) found that

nitrate was least effective in reducing numbers of E. penetrans. Heald and
Burton (I968) reported that organic nitrogen in the form of activated sewage

sludge reduced nematode populations more than inorganic nitrogen. Unless
phytotoxic levels were used, nematode population densities decreased with
increasing amounts of nitrogen. Huber and Watson (I974) reported that the
form of nitrogen was very important for the control of many plant diseases;
however, Workman e_t 91. (I977) was unable to find any differences in soil
ammonium or nitrate and found varying levels of nitrate in potato petioles
between fumigated and non-fumigated plots. Evidently, other factors were
operating directly on the nematode, or indirectly through the host. Nematodes
in Manitoba soils generally decreased in clay with increasing nitrogen, but
numbers increased in smd with increased nitrogen, indicating that soil factors
might be important (Kimpinski 8. Welch, I97I).

Reductions in population levels of plant-parasitic nematodes has also been
achieved with the application of chemical nematicides. Nematicide usage in
the U.S. has increased dramatically since the discovery of I,3-D (mixtures of
l,3-dichloropropane and l,2-dichloropropenes plus other C3 hydrocarbons) in
I943. Use of soil fumigant nematicides is becoming increasing cost-prohibitive
and is restricted in most cases to use in high value crops. Many are phytotoxic
to plants and must be applied several weeks before crops are planted.

Many factors influence the efficacy of nematicides. Goring (I962, I967)
has reviewed the physical and biological factors involved in soil fumigation.
Munnecke and VanGundy (I979) have reviewed the movement of fumigants in
soil, dosage responses and differential effects. The important factors

influencing the movement of soil fumigants are the chemical adsorptive

19

characteristics of the toxicant, temperature, moisture, organic matter, soil
texture and soil profile variability.

Most nematicides, to be effective, must be dissolved in the soil solutions
or adsorbed into plant tissue to come in contact with the target organism.
Concentration and contact time are also important in the efficacy of
nematicides. Not only are there considerable differences between organisms in
their response to various concentrations and contact times, but there are
differences between stages of the same organism (Munnecke 8. VanGundy,
I979). Many nematicides are lethal to nematodes because they directly
interfere with vital metabolic life processes. Other nematode functions
including hatching, movement, feeding behavior, orientation and development

may be impaired or inhibited at low nematicide concentrations.

20

LEPTINOTARSA DECEMLINEATA

The Colorado Potato Beetle. (CPB), Leptinotarsa decemlineata Say, is a

 

major foliar feeding pest of many important agricultural crops, including
potatoes, tomatoes, peppers and eggplant. Both adults and larvae feed by
chewing the leaves and terminal growth of the plant. If defoliation is severe,
the plants will die and development of tubers is prevented or yields greatly
reduced.

E. decemlineata is indigenous to the central U.S., where it was originally
observed feeding on various Solanaceous plants. With the introduction of the
cultivated potato into these areas by early settlers, E. decemlineata became a
serious pest of potato. It migrated eastward across the U.S. into new potato-
producing areas, often reaching epidemic proportions. It was introduced into

Europe in the l920's, where it is now a widespread, serious pest of potatoes.

Life History

E. decemlineata is a multivoltine pest with l-3 generations per year,
depending on the climate and local weather conditions. It overwinters as an
adult in the soil. In the spring, adults emerge and begin the primary life cycle,
ovipositing almost immediately. Eggs are laid in clusters on the underside of
leaves usually after a brief feeding period. CPB has four larval stages. The
fourth stage burrows 2-6 inches into the soil and pupates. After a short
pupation period ranging from 7-2l days (Olsen e_t a_l., I980), it emerges as an
adult md soon mates, repeating the cycle. The number of generations is largely
a function of temperature. The life cycle can be completed in 30 days,

depending primarily on temperature.

21

M

Many of the biological and physiological processes governing the growth,
development and survival of E. decemlineata are environmentally determined.
These include overwintering, spring emergence, egg laying, hatching, larval
development and pupation.

Overwinterim. During the. hibernation phase, CPB survives best in a
moderately dry soil with temperatures above -8 C (Hurst, I975). The depth
below the soil at which beetles hibernate depends on three factors: soil type,
moisture and temperature. These are important in determining overwintering
survival and spring emergence. Hurst (I975) reported that depth of penetration
is shallow in clay soils and deeper in sandy soils. Burrowing to greater depths in
sandy soil provides greater protection from environmental extremes and
decreases the rate of overwintering mortality. Different soils have different
heating and moisture retention characteristics and affect not only
overwintering survival rates, but also emergence of spring adults.

Spring emergence is directly related to soil temperature and depth of
hibernation. Soil temperatures of 9-l4 C is the temperature threshold for
spring emergence (Olsen 3 a_l., I980; Hurst, I975). First emergence is from
shallow overwintering sites. This affects the spring emergence distribution
pattern because threshold temperatures are not reached or maintained
' uniformly through the entire soil profile or between soil types. Wegorek (I959)
studied the emergence rate in relation to temperature. He reported that total
emergence spans about 30 days with the largest percentage occurring during a
l0-day period when soil temperatures reach 20 C.

After spring emergence, beetles begin searching for feeding and

oviposition sites. This may require a short dispersal phase. Wind velocity and

22

direction dictate the location of host and suitable oviposition sites by weak

flying adult beetles (HJrst, I975). Although not essential, beetles usually feed
for a short period before mating and egg laying (Gibson 3 a_l., I925).

Copulation may not be necessary for females because some inseminated the
previous year remain fertile through the winter.

Oviposition. Eggs are laid during the day, singly or in clusters on the

 

I undersides of leaves. The greatest number of egg masses are deposited on the
largest leaves, usually on or near the 3 terminal leaflets of the compound
potato leaf (Gibson 91 a_l., I925). The eggs are cemented to the leaf
undersurface, an egg mass consisting on the average of about 30 eggs. Much
larger and smaller egg masses have been reported (Kowalska, I969). Gibson 91
1': (l925) reported that the number of eggs per mass varies between 6 and l29.
The total number of eggs 0 female oviposits varies from 200 to 800 (Hurst,
I975; Kowalska, I969). After depositing the first egg mass, the female usually
rests for one or more days. Egg laying may continue over an extended period of
time.

Photoperiod directly affects oviposition rates, especially of first and
second generation females. Eggs are laid by females which have emerged only
during times of sufficiently long photoperiods. Short daylengths (< I5 h) cause
females to cease oviposition and begin diapause (Kowalska, I969). This results
in a decrease in overwintering mortality and an increase in post-hibernation
fecundity.

Temperature also affects fecundity. Wegorek (I959) gives the threshold
temperature for oviposition at l8 C while Alfaro (I949, cited in Olsen _e_t_ g_l.,

I980) reports a threshold of I6.5 C. Kowalska (I969) reported that the highest

23

rate of oviposition occurs at 28.7 C, but 2|.7 C is optimum for maximum

fecundity. This increase in the total number of eggs is due to the increased life

span of the female at the lower temperature.

Food quality is an important factor affecting fecundity (Kowalska, I969).
Females feeding on leaves of mature plants and on lower leaves reduces
ovogenesis and oviposition and accelerates the onset of diapause. Maximum
fecundity is realized only when beetles feed on young potato plants (Kowalska,
I969). Plant and varietal difference also influence oviposition (Ting 8.
Fraenkel, I968).

EggDevelopment and Hatching. The length of the egg stage varies with
environmental conditions. Temperature is the most important factor. The
threshold for egg development is l2-l3 C, with maximum developmental rates
reported at 30.5 C and 24.4 C (Hurst, I975). Under field conditions, Chlodny
(I975) reported developmental times ranging from 4 to ID days in warm
climates, and 5 to 2l days in cold areas.

Larval Development. Temperature is by far the most importmt climatic
factor governing the rate and duration of larval development. The threshold for
larval development is _c_ir_cc_I l2-I3 C, if other conditions are ideal (Hurst, I975).
The upper threshold is 33 C. DeWilde (I950, cited in Hurst, I975) considers a
field threshold temperature as l7 C for first and second larval instars.

Under field conditions, Larczenko (I958) reports a range of 2 I-43 days for
total larval development. Karg and Trojan (I968) give the average duration per
stage as L|-3 days, Lz-S days, L3-9 days and La-IS days. Johnson (I9l6)
reports total larval developmental times of l4-I9 days in Washington, D.C.

PUpal Development. Pupal development occurs at I5-I6 C and above with

the time ranging from 7-2l days (Olsen e_t 91., I980).

24

Mortality

Many factors affect CPB mortality. Temperature is the most important
climatic parameter. Other factors such as precipitation, soil moisture, soil
type, humidity, food quality and food quantity have also been shown to
influence CPB survival.

Temperature exerts a primary influence on CPB mortality, depending on
the stage of development. Adult beetles can withstand temperatures to 58-60
C and temperatures as low as -I0 C (Hurst, I975). Soil temperatures of -l2 C
are lethal to hibernating CPBs (Chittenden, I907). Larvae are destroyed at 35
C and temperatures below 0 C, as are the eggs. Gibson 31 g_l_. (I925) observed
that other temperature-related processes are operating which affect mortality
of CPB life stages. Egg cannibalism by CPB larvae is temperature-dependent,
frequently occurring during periods of cold stress.

Rainfall is the second most important environmental influence affecting
survival of E. decemlineata. First and second instar are especially vulnerable
to heavy rainfall. During periods of heavy downpours, small larvae are washed
off the plant and perish in pools of soil water beneath the plant.

Excess soil water also affects overwintering mortality. Death occurs as a
direct result of submersion, indirectly by creating optimum conditions for the
development of disease pathogens and by limiting the beetles to the surface
layers of soil where they die of frost during harsh winters (Hurst, I975).

Excess soil moisture can cause pupal mortality as high as 80%, compared
to 30-40% in moderately moist soil (Olsen gt 2L, I980). Other factors such as
the influence of rainfall and snow cover protect hibernating CPBs from cold
temperature extremes (Hurst, I975). Winters with little snow permit frost to

penetrate deeply into the soil and increase overwintering mortality. Harcourt

25

(I97I) reported that frost mortality may be as high as 70% during Ontario

winters.

Starvation is an importmt mortality factor. Due to the aggregated
spatial distribution of larvae, food shortages may occur in very small areas of
the field. As the food supply diminishes, larvae begin dispersing in search of
food. When the limit of food supply is reached, the larvae starve, resulting in

late season population decreases.

Food Consumption

Feeding by E. decemlineata adults begins soon after emergence of spring

 

adults. They feed between periods of egg deposition on newly emerging potato
seedlings. This continues until the end of the oviposition phase and death of the
adult. I

After emerging from the egg, first instar larvae often feed on the egg
shell and frequently on other unhatched eggs before migrating to the top of the
plant. Small quantities of leaf tissue may be consumed before the first molt.
After the first molt, second instar larvae feed on newly expanding leaf tissue,
preferring the more succulent, interveinal portions of the leaf (Gibson 91 91.,
I925). After the second molt, leaf feeding continues, which now includes the
midribs and larger veins of the leaf. Most feeding and, correspondingly, most
plant damage occurs after the third molt. If fourth stage larvae are numerous,
rapid defoliation cm occur, resulting in both the death of the plant and reduced
potato yield. In the absence of leaf tissue, CPB larvae may feed on the main
stems of the plant or, because of overcrowded conditions, may begin dispersing
away from the plant in search of a new food source. Feeding continues at a

lower rate through the night. Heaviest feeding occurs 2-4 hours before twilight

26

(Chlochy, I975). Feeding continues to within a few hours of pupation.

Consumption by adults may be very damaging, especially to very young plants

and especially later in the season when adults are abundant.

Rates of food consumption by E. decemlineata is dependent on the quality
and qumtity of food available. Wegorek (I959) showed lower nutrient and dry
matter content of leaves grown in diffuse light which significantly affected the
subsequent feeding habits of E. decemlineata. Food consumption by adults
begins at I3 C and peaks at 25 C, almost doubling between 2I C and 25 C
(Chlodiy, I975). Trojan (I968b) reported that female beetles consume l5.5
cal/day at 20 C, whereas males consume l7.4 cal/day. Grison (I950, cited in
l-iJrst, I975) related food intake to temperature and reported maximum food
consumption at about 25 C. Above this temperature, most food was consumed
noctumally. Below 25 C, most food was consumed during the day.

Wegorek (I959) reported similar values for larval consumption patterns.
At 20 C, food consumption by larval stages was 0.2, l.5, 5.2 and 23.0 cmz,
respectively, of which more than 75% of the total 29.9 cm2 was consumed by
the fourth stage larvae. Chlodty (I967) reports the percent total consumption
for larval stages as: L|-2.8%, L2-6.396, L3-20.896 and L4-7096. Gibson (I925)
reported similar findings of larvae consuming 28.0 cm2 of potato leaf within a
developmental period of I6 days. Hurst (I975) found that certain temperature
levels are essential for larval food consumption, with a lower temperature

threshold of l2 C.

Population Dynamics
Seasonal population fluctuations of E. decemlineata are dependent on the

survival of each life stage. Many of the mortality factors previously described

27

are important in determining population trends during the season. Reductions

in the potential population size begin with overwintering mortality of adults in

the soil. This is partially determined by the activity of the adult beetles before
the onset of diapause. Females which begin egg laying before hibernating
decrease their chances of survival by depleting the critical body fat reserves
necessary to endure the winter. If they do survive the winter, fecundity rates
are lower. This contributes to between-season population fluctuations of CPB.
The effects of adverse weather conditions (i.e., rainfall, subnormal
temperatures) increase the mortality of newly emerged adults and prevent the
laying of a full complement of eggs.

The reduction in egg population is due mainly to the cannibalistic nature
of adults and newly emerged larvae (Trojan, I9680). Karg and Trojan (I968)
determined the reduction in the total number of eggs from cannibalism to be
between S and I896.

During the first and second instars, the principal mortality factor
contributing to seasonal population fluctuations is rainfall. During heavy
downpours, small larvae are washed from the plant to the ground where they
perish in pools of surface water. Mortality caused by natural enemies can be
significant during these initial larval stages. Overall mortality during these
stages may be as high as 30-72% (Karg and Trojan, I968).

Food quantity is a major factor determining the survival of third and
fourth larval instars. CPB larvae hatching from eggs laid late in the season by
adult females may not have enough foliage available to sustain normal growth
and development through the larval stages. As the food supply diminishes,
larvae begin migrating both within and between potato plants. When the limit

of food supply is reached, CPB search for food. Even if food is available, larvae

28

may not have enough developmental time to complete metamorphosis before

perishing during vine kill or harvesting. The number of larvae dying from

starvation is density-dependent. As larval numbers increase, available
resources decrease and mortality due to starvation increases.

Once the food supply is exhausted, larvae starve and the adults emigrate
in search of other food resources. Harcourt (I97I) showed that population
trends are largely controlled by summer adult survival. Emigration, resulting
from limited food supply, is regarded as the principal density-dependent factor
responsible for numerical change in the population from generation to
generation.

Harcourt (I97l) reported that there are no natural control agents
effective in preventing the CPB from overpopulating its food supply in Ontario.
Karg and Trojan (I968) also reported that the natural enemy complex played an
insignificant part in reducing population levels of CPB and their impact on plant
defoliation and yield. This included many of the general predators such as
ground beetles and lady beetles on eggs and other larval stages.

Hurst (I975) reported that two natural enemies in England, 399%

maculiventis and Lebia gandis, have not been successful in controlling E.

 

decemlineata because both had higher temperature and humidity requirements
for survival. Perillus bioculatus and Doqphorophagg dorgphorae may be
effective in controlling endemic populations of CPB (Harcourt, I97I). Mention
is made of an entomophogus fungi (Beaveria effusa) and a bacterial pathogen
(Cocobacillus leptinotarsae) contributing to CPB mortality (Hurst, I975).
Parasitism and predation rates are influenced by many factors, including
changes in the spatial structure of the population. During the early season,

populations of CPB are characterized by a significant degree of aggregation

29

(Karg and Trojan, I968). As the season progresses, the population distribution
changes from an aggregational one to a random one with gradual dispersion of
CPB aggregates. This distribution changes with a simultaneous increase in the
density of CPB larvae, causing an increase in the number of contacts CPB
larvae have with natural enemies. CPB mortality due to natural enemies

increases with time and dispersal of larvae and adult beetles.

30

SOLANUM TUBEROSUM

Solanum tuberosum (Fig. l) is a widely cultivated tuber-bearing food crop
of worldwide distribution. It is indigenous to the Peruvian and Bolivian Andes
of South America as S. tuberosum spp. andigena (Harris, I978). It was
introduced into Europe from the New World in l570 by returning Spanish
conquistadores. From this Spanish source, the potato spread throughout Europe
and the Mediterranean and finally into North America in I62 I.

Originally, S. tuberosum spp. andigena was unsuited to the long summer
days and cold nights of Europe. Yields were poor with unsightly, misshapen
tubers. Selections for earliness resulted in new varieties adapted for the
European and North American climates. This eventually precipitated its
widespread cultivation and consumption among the peasants of Europe and
pioneers of the New World. Today potatoes are a major food staple.

The genus Solanum contains over 2000 species. In addition to S.
tuberosum, seven other cultivated species and l54 wild species of potato are
recognized. Through the efforts of plant geneticists, numerous potato cultivars
have been developed with adaptations to various environmental conditions,
consumer demands and production strategies.

Since the Irish potato famine of I845, which killed or displaced an
estimated two million people, much emphasis has been placed on the study of
the potato crop. Numerous studies have examined the influence of various

biotic and abiotic factors on plant growth, development md yield.

Life History
Potatoes are generally best adapted to cool temperate regions. They are

usually grown from vegetative seedpieces; however, propagation from seed is

31

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32

 

 

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(after Milthorpe and Moorby, 1960).
L = leaf area index, Ep = potential rate of net assimilation

33

possible. Sprouts initiated from the mother tuber produce the daughter plant
did the subsequent crop. Until sprout emergence and leaf expansion, the young

potato seedling is dependent on the carbohydrate reserves of the mother tuber.
This sets a lower limit on the seed tuber size (Ivins & Milthorpe, I963), with
final tuber yield increasing with increasing seedpiece size (Harris, I978).

lvins and Milthorpe (I963) have divided the seasonal life history of the
potato plant into three phases (Fig. 2). The first phase of growth is pre-
emergence. This involves the initial development of roots and sprouts from
stored carbohydrates in the mother tuber. Developmental rates are dictated
primarily by soil temperature and seedpiece size (lvins & Milthorpe, I963). The
second phase is the haulm growth phase. After sprout emergence, the plants
become photosynthetically active. Growth accelerates and the leaves, stems
and roots increase rapidly in size, number and weight. Growth during this phase
is dictated by environmental conditions, such as nutrient availability and the
presence of pest organisms. The tuber growth phase is the final growth stage,
being closely interrelated with and overlapping the haulm growth phase. It
begins with tuber initiation and concludes at harvest. Tuber weight is the final
result of the growth rate of leaves and stems, the production and distribution of
assimilates, the time of tuber initiation and the time of senescence of the

foliage.

Environmental Influences

Weather is the most important single factor influencing the growth,
development and yield of potatoes. It is extremely complex and cannot be
defined as simply a combination of light, temperature and soil moisture, but
must be considered in terms of a number of interacting forces impacting on the

plant.

34

Temperature. The potato is a cool weather crop. It is ideally suited for
areas where the mean annual temperature is S-IO C and where the mean
temperature of July is not over 2| C (Hardenburg, I949). Temperature affects
plant respiration and transpiration. The optimum temperature for vegetative
growth is 20-25 C, depending on the variety tested (Borah e_t a_l., I960; Borah &
Milthorpe, I962). The potato plant cannot survive extended periods of frost,
with extensive damage caused by a disruption of cellular membranes, loss of
cytoplasmic water and leakage of ions (Harris, I978).

Low temperatures retard vegetative growth and tuber initiation (Borah g
91., I960; Borah & Milthorpe, I962). High temperatures delay tuber induction
md decrease the rate of tuber development (Werner, I934). Yamaguchi e_t 91.
(I964) reported that the optimum temperature for tuber formation of Russet
Burbank potatoes is l5-25 C. At temperatures above 26 C, stolons are short
with tubers misshapen, forming sessile to the plant near the soil surface. Borah
31 g. (I960) showed that high temperatures favor emergence and delay tuber
initiation. The earliest tuber initiation and the greatest number of tubers were
encouraged by low temperatures. After tuber initiation, tuber growth was
reported to be fastest at a temperature of l5-20 C. Bushnell (I925) reported
that tuber yields decreased with increasing temperature from 20-29 C, with no
tubers forming at 29 C. The delay in tuber initiation and decrease in the rate
of tuber growth at high and low temperature extremes is due to the balance
between carbohydrate metabolism and plant maintenance.

_L_igm. Light intensity influences the rate of photosynthesis which directly
affects growth and development through the production and distribution of
assimilates (lvins & Milthorpe, I963). Photosynthesis increases with increasing

light intensity until an optimum level is reached. Chapman and Loomis (I953)

35

demonstrated that maximum rates of photosynthesis occurred when light
intensities of 80,000 lux were reached. Light saturation levels occur only when
water and C02 are limiting (lvins & Milthorpe, I963). Tuber weights are higher
at higher light intensities because of the influence of light intensity on
photosynthetic rate (Harris, I978).

In general, growth and development is influenced by light intensity, since
tuber formation, maximum stem elongation and plant senescence occur earlier
at higher light intensities (lvins & Milthorpe, I963). At high light intensities,
there is a greater total production of dry matter, and a higher percentage of
dry matter is used in tuber production. Early tuber initiation, although
favorable for increased tuber growth, may be offset by early plant senescence.

Growth and development is influenced by daylength and considerable
differences in plant response to photoperiod exist among potato varieties and
developmental stages. lvins md Milthorpe (I963) reported that most potato
varieties require a short daylength (IO-l4 h) for maximum tuber production.
Above a daylength of IQ h, tuber growth is inhibited and excessive development
of the foliage occurs. Below a daylength of IO h, tuber growth is stimulated
and top growth inhibited. Early varieties have a high critical daylength (IS-l7
h), whereas late varieties have a lower requirement (l2-llI h). Early varieties
grow under short days in the spring, and this short day influence promotes tuber
initiation and growth. Tuber formation of the late varieties is inhibited during
mid-summer (long days), obtaining maximum tuber growth during the shorter
days of late summer and early fall.

W. Water is an important factor in potato production. §. tuberosum
is very sensitive to water stress. For optimum vegetative growth and tuber

yield, rainfall or its equivalent, irrigation, needs to be distributed to keep water

36

deficits small to prevent growth inhibition. Water deficits result in smaller,

narrower, spindly-shaped leaflets and decrease yield and quality of tubers

(Epstein & Grant, I973). Haddock _e_t_ 91. (I974) found that the reduction of
integrated water potential from -0.6 to -l.5 bars through the season caused a
35% reduction in potato yields growing in Utah.

Large diurnal fluctuations in the water content of leaves inhibit potato
growth (Harris, I978). This is caused by the inability of the plant to absorb
water at a rate sufficient to replace the water lost through transpiration.
Fluctuations in water content are accompmied by high leaf temperatures
during periods of high transpiration and limited soil moisture. When moisture is
adequate, transpiration maintains leaf temperatures close to the ambient and
prevents wilting. Decreases in the production and translocation of
photosynthates and corresponding decreases in plant growth and yield are
associated with inadequate soil moisture.

Water is important for nutrient uptake. There is an additional increase in
tuber production for every unit of water evapotranspired (Harris, I978). Vitosh
and Warnke (l97l) observed that high rainfall or excessive irrigation causes
considerable losses of nitrogen in sandy soils. Highly mobile nutrients such as
nitrogen were readily leached below the effective rooting depth of the potato
plant, thus requiring an-additional application of nitrogen. Conversely, low soil
moisture levels interfere with the absorption of plant nutrients by decreasing
the availability and concentration of various nutrients in soil solution adjacent
to potato roots.

Timely applications of water can also modify the effects other
environmental factors have on plant growth. Early irrigation during hot, dry

conditions lowers the soil temperature and may indirectly produce earlier tuber

37

set and lead to a more rapid development of tubers than would normally have

occurred (lvins & Milthorpe, I963). Over-irrigation may result in reduced yield

by creating conditions favorable for disease development (Harris, I978) or by
increasing losses from bruising and skinning of tuber during harvest

(Hardenburg, I949).

Plant Nutrients

Optimum production of high quality potatoes requires at adequate supply
of the proper nutrients throughout the growth of the plant. Potato soils differ
in their ability to provide certain nutrients at critical times during the season.
Most mineral nutrients essential for plant growth have general effects on the
plant. This can very over a wide range of fertilization rates md from season to
season. Many of the mineral elements have specific biochemical roles and
relatively small effects on growth within a narrow range of supply. Other
nutrients, such as the macronutrients (Nitogen (N), Phosphorus (P), Potassium
(K)), have much broader effects over wider ranges of supply.

Nitr99en. Nitrogen is absorbed by plants primarily in the form of nitrates
in the soil rhizosphere. Once absorbed by the plant, the nitrate is reduced to
ammonium and combined with carbon molecules to form amino acids. The
amino acids are linked to form enzymes which control the metabolic processes
of the plant. In addition to this role, nitrogen is also an integral part of the
chlorophyll molecule.

Phosghorus. Absorption of phosphorus by potato roots occurs primarily as
inorganic monovalent or divalent phosphate ions. Phosphorus is relatively
immobile in soils, being tightly bound to soil particles. Phosphorus, like

nitrogen, is an extremely important structural component of many compounds

38

synthesized within the plant, and performs an invaluable role in energy

metabolism (Tisdale & Nelson, I975). The hydrosis of high energy phosphate

bonds is almost exclusively used to drive chemical reactions.

NJtrient absorption is a complex process involving the movement of
mineral nutrients, primarily from the soil, into the roots of the plant. From the
roots they are distributed to the various parts of the plant, where they are
utilized in various metabolic processes. During the early stages of growth, the
mother tuber provides the ready source of organic and inorganic nutrients
necessary to sustain growth (Moorby, I968; lvins & Milthorpe, I963). With the
development of the root system, the plant begins extracting nutrients from the
soil. The rate at which these nutrients are incorporated into the plant is then
dependent on a number of complex environmental, physiological and edaphic
factors. .

Uptake of plant nutrients into the plant is directly related to the nutrient
status of the soil. Increases in nutrient supply, through fertilizer application,
invariably show increases in total nutrient uptake and percent nutrient content
in dry matter yield (Werner, I934; McCollum, l9680; Mukherjee Q 91., I966). In
some cases, uptake has been so extensive that nutrient concentrations in tubers
have approached human toxicity levels (Kirkham e_t_ 91., I974).

Water is also important in nutrient uptake. Roots come in contact with
more nutrients when growing in moist soil than when growing in a drier one
because growth is more extensive. Decreases in uptake rates have been shown
to coincide with periods when soil moisture deficiencies were increasing
(Tisdale 8: Nelson, I975). Short-term fluctuations do not appear to affect the
plant, but can have a significant impact on the plant if soil moisture stress and

decreased nutrient absorption continue for m extended period of time (Munns 8.

39

Pearson, I974). Nutrient absorption is a very complex process depending

primarily on soil moisture, the concentration adjacent to the potato root, soil

temperature, total absorptive surface of the root and the rate of metabolic

processes occurring at various developmental stages of the plant (Harris, I978).

Effects on Growth, Development and Yield. Changes in nutrient supply
affect growth, development and yield, primarily by influencing the net amount
of photosynthesis in the plant. Differences in N and P supply are directly
related to the temporal changes in size and efficiency of leaves, and to the
changes in the ontogeny of the plant (McCollum, l968b).

Temporal changes in plant ontogeny have been studied by examining what
affect various nutrient levels have on the growth and‘senescence of leaves and
the initiation and bulking of tubers. In general, it has been observed that high
levels of N and P delay tuber initiation and correspondingly the onset of the
tuber bulking phase (Ivins & Bremmer, I965, cited in Harris, I978; Kable & Mai,
l9680). This is apparently caused by an increase in the growth and development
of leaf tissue by diverting assimilates to leaves which could be used for initial
tuber growth. The influence that high levels of N and P have on delaying tuber
initiation and bulking and, ultimately, tuber yield, is partially offset by the
affect these nutrients have on the development and maintenance of leaf area.

Leaf area of a plant depends on the number and size of leaves. Net
photosynthesis is a function of total leaf area, net assimilation rate (E) and the
longevity of leaves or leaf area duration (D). Increases in the levels of N or P
greatly increase leaf area (Harris, I978; Lorenz, I947; Dainty 91 a_l., I959; lvins
& Milthorpe, I963). Increases in leaf area increase tuber bulking rates, and

increases in N and P supply cause apical meristems on the plant to develop,

40

accounting for much of the increase in leaf area. N also causes increases in
leaf area through leaf production and expansion of existing leaves throughout
the season. P has the some influence but the effects appear earlier and are less
persistent than the effects of N. lvins and Bremmer (I965, cited in Harris,
I978) showed that tuber bulking rates increased with increasing leaf area.

Dyson and Watson (I97l, cited in Harris I978) reported that potato yield
is closely related to leaf area duration (D) and leaf area index (LAI) during the
growth period of the crop. Tuber yields depend in part on the total leaf area
(estimated by LAI) produced and the interval of time between tuber initiation
and leaf senescence. It has been repeatedly shown that high levels of N prolong
the life of the leaves while P has the opposite effect of shortening it (Harris,
I978). Tuber yields are thus increased because application of high levels of N
or P increase net photosynthesis by either increasing the siZe of the leaf system

or by prolonging the life of leaves or both.

42

ROLE OF SOIL NUTRIENTS AND NEMATICIDES
ON s. TUBEROSUM AND a. PENETRANS

In I978 and I979, studies were conducted to examine the influence of
selected production management inputs on the growth, development and yield
of 9. tuberosum and the population dynamics of E. genetrans. Each experiment
during both years consisted of three fertilizer levels and three insecticides md
nematicide treatments. In I978, §. tuberosum (cv Superior) were used to
evaluate the interaction of three nitrogen levels and three nematicide
treatments. A second experiment in I978 examined two nitrogen levels and
five nematicide treatments (Appendix A). In I979, §. tuberosum (cv Superior
and Russet Burbank) were used to evaluate the interaction of three phosphorus

levels and three nematicide treatments.

 

 

 

 

 

44

MATERIALS AND METHODS

Field experiments were conducted in I978 and I979 to evaluate the role
of soil nutrients md nematicides on the growth of _S_. tuberosum and the
population dynamics of E. 9e_netrans. Two potato cultivars (SUperior and Russet
Burbank) were grown on a McBride sandy loam soil (9m fragiothods) at the
Montcalm Potato Research Farm in Entrican, Michigan. The farm is separated
into two large north-south rectangular blocks (Fig. 3). During any year, one
block is utilized for current experimental research while the other black is
spring planted to rye or alfalfa. The following spring it is planted. Blacks are
rotated every other year to enhmce soil organic content and to reduce

populations of soil borne orgmisms and insects detrimental to §. tuberosum.

PlantichProcedure

Each year, seed beds were prepared by disking the field plots to break the
soil md to cut the rye or alfalfa. The field was then plowed and planted with a
2-row Lockwood potato planter. Seedpieces (whole certified seed, 3 S cm dia-
meter) were planted on May 22 and 23, I978, and May l6 and I7, I979. Each
plot consisted of four rows 0.86 m wide and l5.24 m long. Seed spacing was 20
cm for Superior and 30 cm for Russet Burbank. All plots were irrigated with a
solid set sprinkler system according to need determined by measurements of

evapotranspiration.

Samgling Procedure

Plant growth and development was measured at various intervals during

I978 and I979. The experimental area was first divided into 5 blocks of equal

45

size to compare sampling variation within and between treatments. In sampling
foliage, two plants were randomly selected from the outside rows of each plot.
The soil immediately below each plant was carefully removed to a depth of 99.
0.35 m. In I978, the soil directly below each plant sample was hand-sifted for
roots and tubers. In I979, it was sifted through a series of sieves in a hmd-
driven mechanical shaker. Soil and plant material was first passed through a
0.95 cm hardware cloth and then through 0.3l cm hardware cloth. Roots and
tubers removed from both screens were bagged and returned to the laboratory
with the foliage and a representative soil sample of I000 cm3. Tuber numbers
were also determined at this time for each treatment and sampling period.

Soil and root populations of E. wetrans were estimated from samples
taken at these times. Nematode extraction techniques for both soil and roots
were the same for both I978 and I979. Soil samples for nematode analysis were
taken by core sampling (IS-20 cores) the two outside rows of each plot and
later, after plant germination, by removing the soil adjacent to the roots of the
plant. Root samples were derived from plants returned to the laboratory for
plant growth analysis. Soil and root populations of E. wetrans were
determined using the centrifugation-flotation technique (Jenkins, I964) and
shaker technique (Bird, I97I), respectively. Estimates of soil and root
nematode population densities were based on ID cm3 of soil and 0.l gram of
root in I978, and l00 cm3 of soil and one gram of root in I979. The
quantitative differences in the quantities of soil and root material used for
estimating population densities of E. 9e_netrans in each of the two years were
determined by economic and time constraints. In I978 the time and labor
required to process nematode samples was not available and estimates were

based on the smaller root and soil samples. At various intervals during the I978

46

season, both the ID and l00 cm3 and OJ and LO gram soil and root samples

were processed to compare the efficiency and reliability of the estimates

achieved by both methods. This was achieved first by agitating the ID ml vial
of nematode suspension and extracting I.0 ml with a l.0 ml syringe. Nematodes
were counted in a circular petri dish under a ISX dissecting microscope.
Immediately afterward, the remaining 9.0 ml of nematode suspension was

counted and recorded.

Harvesting Procedure

Tuber yields were calculated from the harvest of the two center rows of
each plot with a self-propelled potato harvester specifically developed for field
research (Chase 91 91., I978). Tubers from each plot were graded, weighed md
bulk lots brought to the laboratory for specific gravity determinations. Specific
gravity was determined after weighing the bulk samples in air and then in water
and applying these data to the equation:

S.G. = (wt. in air) / (wt. in air - wt. in water)

A completely random block-two factorial design was used, with each
treatment replicated five times. The data were subjected to an analysis of
variance to statistically examine differences in plant growth, development,

yield and nematode control.

Nitr99en

Two experiments were established in I978 to examine nitrogen levels did
their interactions with selected insect and nematode control programs, and to
monitor growth, development and yield.

In the first experiment (Table I), cv Superior was evaluated at three

47

nitrogen rates (84, I68 and 336 kg/ha) and three pesticide treatments (control,
aldicarb (Temik ISG), and I,3-D + MIC (Vorlex)). All plots received 84 kg/ha of
N, P205 and K20 (l5-I5-l5) as a starter fertilizer banded S cm to the side and
below the seed piece. The plots to receive an added nitrogen treatment were
side-dressed with urea (45% N) at an application rate of l l2 kg/ha on June I3,
I978, and either 84 kg/ha or I40 kg/ha on June 22, I978.

Phosphorus

Two experiments were established in I979 to examine varying phosphorus
levels and their interactions with selected insect and nematode control
programs and to monitor growth, development and yield. In the first
experiment, seed pieces (cv Superior) were planted in plots treated with three
levels of phosphorus (0, 56 and I68 kg/ha) and three pesticides (control, aldicarb
and I,3-D + MIC). In the second experiment, seed pieces (cv Russet Burbank)
were planted in plots receiving treatments identical to those in experiment one.
In each experiment, those plots to receive phosphorus were supplied with either
56 or I68 kg/ha P205 at planting. The rows in each plot were hilled and side-
dressed at a rate of I62 kg/ha urea (45% N) on June 20, I979.

The controls in each experiment, during both years, received no soil
pesticides; however, the foliar insecticide Methamidophos (Monitor IOG) was
used as needed throughout the entire experiment to minimize the impact of
foliar-feeding insects. The soil-applied pesticides, except I,3-D + MIC, were
applied at planting in the fertilizer furrow at a rate of 3.4 kg/ha active
ingredient. The I,3-D + MIC was injected on a broadcast basis to a soil depth of
20 cm at the rate of 93.5 kg/ha on May 3, I978, and on May I, I979.

48

RESULTS

Nitrggen

Both nitrogen and nematicides influence final tuber yields of 9. tuberosum
(Table I). In the absence of a nematicide, the higher two rates of nitrogen had
no significant (P=0.5) influence on tuber yield. In the presence of I,3-D & MIC
or aldicarb, increasing rates of nitrogen resulted in significant (P=0.05)
increases in final tuber yield. Total yield from plots treated with either
aldicarb or. I,3-D 8 MIC were significantly (P=0.05) higher than that of the
controls. Highest total yields were observed in the 336 kg/ha nitrogen plots
with aldicarb and I,3-D & MIC.

Medium size A tuber (5-8 cm diameter) yield showed similar results to
that of total yield (Table I). Aldicarb and I,3-D & MIC with nitrogen rates
above I68 kg/ha significantly (P=0.05) increased the yield of A size tubers.
Both aldicarb and I,3-D & MIC at the 84 kg/ha nitrogen significantly (P=0.05)
increased the small B size tuber ( > 5 cm diameter) yield compared to the I,3-D
& MIC treatments at the 336 kg/ha and I68 kg/ha nitrogen rates. Aldicarb at
the highest nitrogen rate resulted in the greatest yield of large tubers ( > 8 cm
diameter (Table I». This was significantly (P=0.05) greater than any treatment
at the 84 kg/ha nitrogen rate.

Nitrogen fertilizer had no detectable effect on nematode population
dynamics (Tables 2, 3). There were no significant (P=0.05) differences in soil
population densities of E. fletrans among the plots until the August I, I978,
sample (Table 2). From August I, I978, to harvest on August 2|, I978, soil
population densities of E. Benetrans were significantly (P=0.05) lower in the

aldicarb-treated plots. Based on E. genetrans recovered from root tissue, both

 

49

 

 

 

 

Table l. TUBER YIELD- Influence of selected mana ement inputs on the yield
and grade of 9. tube__r__osum cv Superior)
Treatment Tuber yield (quintaI/ha)

Nitrogen Pesticide 5-8 cm <5 cm >8 cm Total

(kg/ha)
84 Check 266.I 0' I05 ab 5.4 a 285.4 a
84 Aldicarbz 332.l bc I3.6 b 5.2 a 335.2 bc
84 I,3-D & MIC3 3 l6.4 c l3.l b 5.5 a 349.3 c
I68 Cheek 295.0 ab 8.6 a 9.I ab 309.7 (the
I68 Aldicarb 358.l d I |.8 ab I2.8 ab 38l.8 d
I68 I,3-D 8: MIC 379.8 d 9.0 0 I2. I ab 398.7 d
336 Check 28|.8 ab I0.0 ab 7.3 a 300.l ab
336 Aldicarb 378.0 d l0.5 ab 28.2 b 4I6.l d
336 I,3-D & MIC 375.8 d 8.0 a 26.0 ab 409.6 d

 

Column means followed by the same letter are not significantly different

(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i.lha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 I/ha
on May I, I978.

Table 2. SOIL POPULATION - Influence of selected management inputs on soil
populations of E. genetrans on 9. tuberosum (cv
Superior).

 

 

 

 

Treatment E. 9enetrans per I0 cm3 soil‘I

ngfigf" Pemdde l39.2 24:.2 373.5 543.8 768.0 983.3
84 Check I.4 al 0.6 a I.2 a 2.0 a 4.4 d I.6 abc
84 Aldicarbz 0.6 a 0.4 a 0.8 a 0.0 a 0.0 a 0.4 ab
84 I,3-D a MIc3 I0 0 0.2 a I.4 a 2.4 a 0.4 ab I.8 ab
I68 Check 2.4 a 0.6 a 0.8 a 3.4 a 2.0 be 6.8 c
I68 Aldicarb I.2 a 0.4 a 0.4 a 0.4 a 0.0 a 0.0 0
I68 I.3-D & MIC 2.4 a 0.0 a 0.4 a 0.6 a 0.4 ab I.0 ab
336 Check 2.2 a 0.8 a LO 0 2.0 a 3.2 cd 3.8 be
336 Aldicarb 2.4 a 0.2 a 0.0 a 0.6 a 0.0 a 0.2 a
336 l.3-D 8 MIC I.2 a 0.0 a 0.4 a 0.2 a 0.6 ab 2.6 abc

 

lColumn means followed by the same letter are not significantly different

(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied of planting in the fertilizer furrow at a rate of 3.4 kg a.i.lha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha
on May I, I978.

“Degree day accumulation base I0 C.

51

 

§- P. PENETRRNS

Y = 30599 + 10057 X
R2 = .9413

  

HEHN NUMBER I 10 "L SRNPLE I
40
l

 

 

QT l I I T r I I I I

I z 3 4 s 8 7 a 9.
HEHN NUHBER I 1 HL SBHPLE I

 

 

 

Figure 4. Relationship between the number of E, penetrans observed
in 10.0 ml post-extraction sample and a corresponding
l.0 ml subsample.

52

aldicarb and I,3-D 8 MIC reduced population densities of E. Benetrans (Table
3). Aldicarb resulted in the best season-long nematode control.

Least squares linear regression analysis was performed on the mem
population density estimates obtained from the LO ml subsample and the
corresponding l0.0 ml samples. The following significant relationship was
obtained.

Y = 3.599 + I0.57 X

r2 = 0.94I3

where: Y = mean number of E. wetrans per I0.0 ml sample

X = mean number of E. Benetrans per |.0 ml sample
A plot of these data (Fig. 4) shows a highly significant (P=0.0I) positive linear
correlation of 0.9702. As the mean number of E. @etrans increased in the LO
ml subsample, so did the corresponding mean number of E. wetrans observed
in the l0.0 ml sample.

When the data are examined within sample dates, few significant (P=0.05)
differences were detected in root, tuber, foliage or total plant fresh weights
(Appendix B). Plant fresh weight, however, generally increased with increasing
nitrogen md in combination with nematicides. Assuming additive treatment
effects, significant (P=0.05) differences were observed for foliage, tuber md
total plant fresh weights averaged over the entire sample period for the
respective plant parameter. In the presence of I,3-D 8 MIC or aldicarb,
increasing rates of nitrogen resulted in significant (P=0.05) increases in average
seasonal foliage fresh weight (Table 4). These same trends were also observed
in the average seasonal tuber and total plant fresh weights (Table 4). No
significant (P=0.05) differences in average seasonal root fresh weight were

detected (Table 4).

53

Table 3. ROOT POPULATION - Influence of selected management inputs or

root populations of E. enetrans on 9.
tuberosum (cv Superior).

 

Treatment E. metrans per 0.l 9 root tissue‘I

 

 

Nitrogen Pesticide

 

(kg/ha) 373.5 543.8 768.0 983.3
84 Check 6.8 cl 8.8 ab I0.0 cd 3.0 bc
84 Aldicarbz 0.0 a 0.0 a 0.0 a 0.6 abc
84 up 8 MIC3 I.2 a LO 0 I.6 ab 3.4 abc
I68 Check 6.2 bc 7.0 b I5.8 d 3.2 abc
I68 Aldicarb 0.8 a 0.2 a 0.0 a 0.4 ab
I68 I.3-D 8 MIC I.6 ab L8 0 3.6 bc 2.0 abc
336 Check 5.8 bc I0.2 b l0.0 cd 4.2 c
336 Aldicarb I.6 a 0.4 a 4.8 ab 0.0 a
336 I,3-D 8 MIC 0.8 a I.2 a 4.0 bc l.0 abc

 

IColumn means followed by the same letter are not significantly different

(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 I/ha

on May I, I978.

“Degree day accumulation base I0 C.

54

 

 

 

 

Table 4. Influence of nitrogen fertilizer and nematicide on average seasonal
root, foliage, tuber and plant fresh weight of 9. tuberosum (cv
Superior).

Treatment Average Seasonal Fresh Wt. (Grams)
Nitrogen Pesticide Root Foliage Tuber Plant
(kg/ha)

84 Check 7.3 all 260.I a 383.5 ab 666.0 ab
84 Aldicarbz 7.0 a 335.6 a 392.9 ab 738.4 abc
84 I.3-D 8 406’ 6.9 a 365.I bc 468.5 bc 827.2 cd
I68 Check 7.0 a 294.7 ab 4 I 9.4 abc 700.4 abc
I68 Aldicarb 6.9 a 360.2 bc 387.7 ab 799.I bcd
I68 I,3-D 8 MIC 6.8 a 389.I bc 437.l abc 794.l bcd
336 Check 7.8 a 26I.7 a 345.5 a 625.I a
336 Aldicarb 7.5 a 369.3 bc 386.3 ab 793.0 bed
336 I,3-D 8 MIC 7.7 a 424.8 c 480.0 c 889.5 d

 

Column means followed by the same letter are not significantly different

(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i.lha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha
on May I, I978.

55

Phosphorus
In the phosphorus experiment with cv Superior, application rate and

nematicide treatment significantly (P=0.05) increased final yield (Table 5).
Regardless of the pesticide used, yields were higher at the higher phosphorus
rate (Table 5). Within each phosphorus level, total yields increased consistently
from the controls, to the aldicarb and I,3-D 8 MIC treated plots, respectively.
The total yield of plots treated with I ,3-D 8 MIC were significantly (P=0.05)
higher than the controls at the 0 kg/ha and 56 kg/ha phosphorus rates. Highest
total yields were observed in the I68 kg/ha phosphorus plots with aldicarb and
I,3-D 8 MIC. Yields of medium size A potatoes (5—8 cm diameter) showed
similar results to that of total yield (Table 5). No significant differences in
yields of B size tubers ( < 5 cm diameter) were observed. Yields of the oversize
'Jumbo' grade potatoes ( > 8 cm diameter) increased with increasing phosphorus
rate in the controls and aldicarb-treated plots. Both aldicarb at the I68 kg/ha
phosphorus rate and I,3-D 8 MIC at the 56 kglha and I68 kg/ha phosphorus
rates significantly (P=0.05) increased yields over the controls and the 0 kg/ha
phosphorus plots. The control at the I68 kg/ha phosphorus rate and I,3-D 8
MIC at the two highest phosphorus rates significantly (P=0.05) increased the
specific gravity of potatoes over the aldicarb plots at the 56 kg/ha phosphorus
rate (Table 6).

Phosphorus fertilization had no detectable affect on nematode population
dynamics. There were no significant (P=0.05) differences in soil population
densities of E. Benetrans among the plots except for the sample of June 26,
I979 (DD|oc=442.7)(Table 7). Aldicarb significantly (P=0.05) reduced the soil
population density of E. genetrans over the controls and I,3-D 8 MIC

treatments in the 0 kg/ha phosphorus plots. There were no significant (P=0.05)

56

Table 5. TUBER YIELD - Influence of selected management inputs on the yield
of Solanum tuberosum (cv Superior).

 

 

 

 

Treatment Tuber yield (quintaI/ha)
Phosphorus Pesticide 5-8 cm < 5 cm > 8 cm Total
(kg/ha)

0 Check 240.8 el I22 0 I L7 0 265.I a

0 Aldicarbz 277.2 ab I4.7 a 22.4 ab 3 I4.3 ab

0 I,3-D a MIC3 3 I08 be I66 0 25.3 abc 352.6 be
56 Check 277.4 ab I l.8 a I6.8 ab 306.I ab
56 Aldicarb 3 I00 be l2.5 a 32.I bcd 354.7 be
56 I,3-D 8 MIC 333.9 c I42 0 f 42.7 d 390.8 e
I68 Check 3I6.6 be l3.0 a 2|.7 ab ‘ 35I.3 be
I68 Aldicarb 353.6 c l3.3 a 40.8 cd 407.8 c
I68 I,3-D & MIC 363.6 c I3.8 a 33.5 bcd 4I0.7 e

 

lColumn means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i.lha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha
on May I, I979.

57

Table 6. SPECIFIC GRAVITY - Influence of selected management inputs on
specific gravity of Solanum tuberosum.

 

 

 

Treatment

Phosphorus Pesticide Russet Burbank Superior
(kg/ha)

0 Check I.068 el I.066 ab

0 Aldicarbz I.070 a I.066 ab

0 I,3-D 8 MIC3 I.072 0 I067 ab
56 Check I.069 a I.066 ab
56 Aldicarb mm a I.065 a
56 I,3-d a MIC I.072 0 I068 b
I68 Check I.072 0 I068 b
I68 Aldicarb I.072 a I.066 ab
I68 I,3-D 8 MIC I.077 b I.068 b

 

lColumn means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i.lha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha
on May I, I979.

58

Table 7. Influence of selected mmagement inputs on soil population densities
of E. genetrans on 9. tuberosum (cv Superior).

 

 

 

Treatment E. Benetrans per l00 cm3 soil‘t
Phosphorus 46.6 2 I2.3 233.7 442.7 723.2 995.5

(kg/ha) Pesticide)

 

0 Check 28.2 al 4I.0 a 20.6 a I9.6 b 78.2 a 39.0 a
0 Aldicarb 30.4 a 36.0 a l7.4 a. 2.0 a 85.0 a 2.6 a
0 I,3-d 8 MIC 34.8 a 30.3 a I6.2 a I5.6 b 79.0 a 39.0 a
56 Check 42.4 a 39.2 a 20.2 a I2.4 ab I20.8 a 55.6 a
56 Aldicarb 23.0 a 24.0 a 9.6 a 3.0 a 23.6 a 4.2 a
56 I,3-D 8 MIC 29.6 a l6.0 a I 8.4 a 8.2 ab I2.6 a 53.2 0
I68 Check 54.6 a 50.0 a I9.4 a 20.6 b 80.4 a 40.6 a
I68 Aldicarb 42.0 a 36.8 a I2.0 a 2.8 a 25.8 a 8.4 0
I68 I,3-D 8 MIC 32.0 a I3.8 a I4.8 a I0.6 ab I l9.8 a 4 LO 0

 

IColumn means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i.lha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 I/ha
on May I, I979.

“Degree day accumulation base I0 C.

59

differences in root population densities of E. Benetrans among the plots season-
long (Table 8). Based on E. wetrans recovered from root tissue in this test,
aldicarb resulted in the best nematode control.

There were no significant (P=0.05) differences in root, tuber or total plant
fresh weight or tuber number among the treatments season-long (Appendix C).
Foliage fresh weights were generally higher within the I,3-D 8 MIC or aldicarb
treatments at the two highest phosphorus rates. When the fresh weights are
averaged over the entire sampling season, no significant (P=0.05) differences in
root, foliage, tuber or total plant fresh weights were detected between
treatments (Table 9).

In the phosphorus experiment with cv Russet Burbank, application rate
and nematicide treatment contributed significantly (P=0.05) to final yield
(Table l0). Regardless of the pesticide used, yields were generally higher at the
phosphorus rate. The I,3-D 8 MIC of the two highest phosphorus rates
significmtly (P=0.05) increased total yield when compared to the controls at
the 0 kg/ha and 56 kg/ha phosphorus rate and the 0 kg/ha aldicarb plots. Yield
of large size potatoes ( > 8 cm diameter) increased with increasing phosphorus,
and was highest in the I,3-D 8 MIC treated plots (Table l0). Within each
phosphorus level, yields increased consistently from the controls to the aldicarb
and I,3-D 8 MIC treated plots, respectively. The I,3-D 8 MIC at the I68 kg/ha
phosphorus level significantly (P=0.05) increased the yield of large size tubers.
The yield of small B size tubers (> 5 cm (diameter) was significantly (P=0.05)
greater in the 56 kg/ha phosphorus control plots than in the control plots than in
the control treatments at the lower phosphorus level. Regardless of the
phosphorus rate, yield of A size potatoes (5-8 cm diameter) was highest in the

I,3-D 8 MIC treated plots (Table l0). Yield of A size potatoes was

60

 

 

 

 

Table 8. Influence of selected mmagement inputs on root population densities
of _P_. Eetrans on 9. tuberosum (cv Superior).

Treatment E. 9enetrans per gram root tissue“
Phosphorus Pesticide 233.7 442.7 723.2 995.5
(kg/ha)

0 Check I9.2 el 56.2 a I78.2 a 94.6 a

0 Aldicarbz 2.6 a I LO 0 6.4 a 6.0 a

0 I,3-D a MIC3 I5.4 a 20.0 a 206.0 a 74.0 a
56 Check I8.6 a 24.2 a 205.2 a l8l.6 a
56 Aldicarb 7.0 a I4.0 a 5.6 a 25.2 a
56 I,3-D 8 MIC I6.2 a I7.0 a l49.4 a I50.6 a
I68 ' Check 24.6 a 36.0 a I75.0 a 2 I3.8 a
I68 Aldicarb 2.8 a I0.8 a 9.0 a 5.6 a
I68 I,3-D 8 MIC 8.8 a l9.2 a I73.2 a I48.2 a

 

|Column means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i.lha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 I/ha
on May I, I979.

“Degree day accumulation base l0 C.

61

 

 

 

 

Table 9. Influence of phosphorus fertilizer and nematicide on average seasonal
root, foliage, tuber and plant fresh weight of 9. tuberosum (cv
Superior). _—
Treatment. Average seasonal fresh wt. (Grams)
Phosphorus Pesticide Root Foliage Tuber Plant
(kg/ha)
0 Check I0.8 a 77.5 a 305.4 a 4I4.3 a
0 Aldicarb I l.0 a I07.6 a 344.6 a 482.8 a
0 I,3-D 8 MIC I0.5 a 84.7 a 367.7 a 484.3 a
56 Check I2.5 a 85.I a 329.8 a 448.5 a
56 Aldicarb l0.3 a 79.5 a 38l.9 a 493.5 a
56 I,3-D 8 MIC I0.4 a I l5.3 a 4| I.8 a 556.4 a
I68 Check I0.3 a 92.4 a 358.2 a 48l.7 a
I68 Aldicarb I0.7 a I23.6 a 400.4 a 558.3 0
I68 I,3-D 8 MIC I0.4 a I20.6 a 443.0 a 595.l a

 

lColumns followed by the same letter are not significantly different (P=0.05)
according to the Student-Newman-Keuls Multiple Range Test.

2Applied of plant in the fertilizer furrow at a rate of 3.4 kg a.i.lha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha

on May I, I979.

Table I0. TUBER YIELD - Influence of selected management inputs on the
tuber yield of 9. tuberosum (cv Russet Burbank).

 

 

 

 

Treatment Tuber yield (quintal/ha)
whiz?“ Pesticide 5-8 cm < 5 cm > 8 cm Misshapen Total
0 Check 204.9 6| 25.2 a 2.5 a 27.2 a 259.7 a
0 Aldicarbz 2 I 9.7 ab 27.4 ab 3.8 ab 49.6 be 300.7 ab
0 I,3-D 8 MIC3 278.7 be 27.I ab 6.3 ab 34.9 ab 346.9 be
56 Check 240.2 abc 35.I b 8.3 ab 29.9 ab 3 I 3.5 b
56 Aldicarb 244.l abc 26.I ab 8.5 ab 58.5 c 337.I be
56 I,3-D a MIC 302.7 c 30.0 ab l3.0 b 42.6 abc 388.3 e
I68 Check 284.0 be 33.4 ab 9.4 ab 34.6 ab 36 L3 be
I68 Aldicarb 234.9 ab 28.3 ab I I.7 ab 72.6 d 347.4 be
I68 I,3-D 8 MIC 299.5 e 28.3 ab 2 I.2 e 34.6 ab 383.5 c

 

lColumns followed by the same letter are not significantly different (P=0.05)

according to the Student-Newman-Keuls Multiple Range Test.

2Applied at plant in the fertilizer furrow at a rate of 3.4 kg a.i.lha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 I/ha

on May I, I979.

63

significantly (P=0.05) increased with I,3-D 8 MIC at phosphorus rates above 56
kg/ha over the control and aldicarb plots at 0 kg/ha. The yield of misshapen
grade tubers generally increased with increasing phosphorus md were highest in
the aldicarb and I,3-D 8 MIC treatments. Yields of misshapen tubers were
significantly (P=0.05) increased by aldicarb at the I68 kg/ha phosphorus rate.
The I,3-D 8 MIC at the I68 kg/ha phosphorus rate significantly (P=0.05)
increased the specific gravity of Russet Burbank potatoes (Table 6).

Regardless of the phosphorus level, soil population levels of E. Benetrans
were consistently lower in the aldicarb plots season-long (Table I I). During the
June 26, I979 (DD|0C=442.7) sample, aldicarb significantly (P=0.05) reduced
soil population densities of _P_. wetrans at all phosphorus rates when compared
to the control treatments at the I68 kg/ha phosphorus rate. Based on l_-"_.
metrms recovered from root tissue in this test, aldicarb resulted in the best
nematode control (Table l2).

There were no significant (P=0.05) differences in root or tuber fresh
weights or tuber number season—long (Appendix D). Total plant fresh weight
was higher in all nematicide-treated plots. Foliage fresh weight was generally
higher at the higher phosphorus rate and in combination with either nematicide.
Phosphorus and nematicide directly influence average seasonal fresh weights
(Table I3). In the presence of I,3-D 8 MIC or aldicarb, increasing rates of
phosphorus resulted in significant (P=0.05) increases in average seasonal foliage,
tuber and total plant fresh weights. No significant (P=0.05) differences in

average seasonal root fresh weight were detected (Table I3).

64

 

 

 

 

Table I I. Influence of selected management inputs on soil population densities
of E. metrans on 9.‘tuberosum (cv Russet Burbank).
Treatment E. genetrans per I00 cm3 soillI
73373:?” Pesticide 46.6 2 l2.3 233.7 442.7 723.2 I I55.9
0 Check I6.8 dl 39.0 ab I4.6 a I5.6 (lb 40.2 d 57.0 be
0 Aldicarbz 2 LB 0 42.8 b 5.4 a 5.8 CI 6.0 d 2.0 d
0 I,3-D8MIC3 23.6 0 I82 db I28 0 I I.4 (lb 37.6 a 45.2 abc
56 Check l5.8 d 37.8 ab I20 0 I3.4 db 37.0 d 32.8 dbe
56 Aldicarb I3.4 a 32.8 ab 4.2 a 5.0 a 23.8 a I.6 a
56 I,3-D a MIC I7.0 d I I.6 CI 9.8 d I2.6 db II.8 d 32.8 dbe
I68 Check 2 I.2 a 29.2 ab I I.2 a l9.8 b 20.4 0 75.4 e
I68 Aldicarb 25.6 d 36.6 ab 5.8 d 4.8 d I0.8 CI 9.8 db
I68 I,3-D a MIC 28.6 a l0.8 O I4.0 0 I28 db l5.4 d 43.2 dbe

 

'Columns followed by the same letter are not significantly different (P=0.05)
according to the Student-Newman-Keuls Multiple Range Test.

2Applied at plant in the fertilizer furrow at a rate of 3.4 kg a.i.lha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 I/ha
on May I, I979. ,

“Degree day accumulation base l0 C.

65

Table I2. Influence of selected management inputs on root population densi-
ties of E. metrans on 9. tuberosum (cv Russet Burbank).

 

 

 

 

Treatment E. Benetrans per gram root tissue‘I
7337,32?” Pesticide 233.7 442.7 723.2 I I55.9
0 Check ‘ I6.6 el 47.0 ab 59.0 a 96.4 ab
0 AIdiedrb2 2.2 a I0.6 a 3.0 a 5.0 a
0 I,3-D a MIC3 38.0 a 40.4 (lb 64.8 6 I348 b
56 Check I2.6 a 65.4 b 54.4 CI 67.0 ab
56 Aldicarb 4.2 a 2.8 a 0.8 a I.6 a
56 I,3-D 8 MIC 22.8 d 29.0 (lb 49.0 d 94.6 ab
I68 Check l8.2 d 22.0 CI) 49.6 a 85.4 ab
I68 Aldicarb 2.8 a 8.6 a 8.4 a 4.0 0
I68 I,3-D a MIC I5.0 a 43.8 (lb 58.0 0 I090 b

 

lColumns followed by the same letter are not significantly different (P=0.05)
according to the Student-Newman-Keuls Multiple Range Test.

2Applied at plant in the fertilizer furrow at a rate of 3.4 kg a.i.lha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha

on May I, I979.

4Degree day accumulation base l0 C.

66

Table I3. Influence of phosphorus fertilizer and nematicide on average season-
al root, foliage, tuber and plant fresh weight of 9. tuberosum (cv
Russet Burbank).

 

 

 

 

Treatment Average seasonal fresh wt. (Grams)

mhzgorus Pesticide Root Foliage Tuber . Plant

0 Check I4.I 6| 2 I 8.5 a 306.I a 559.9 d

0 AIdieerbZ I5.I a 276.7 Ob 355.7 (lb 669.8 d

0 I,3-D 8 MIC3 l5.3 a 333.7 abc 4I4.2 0b 787.9 (lb
56 Check I4.7 a 284.6 a 356.8 (lb 678.I d
56 Aldicarb I6.I a 366.5 abcd 363.5 Ob 769.6 ab
56 I,3-D a MIC I6.2 a 469.8 ed 484.I b 999.2 b
I68 Check I4.8 a 387.8 bed 379.4 (lb 805.8 db
I68 Aldicarb I6.2 0 4| I.4 bed 385.5 Ob 836.I Ob
I68 I,3-D a MIC I7.3 d s I0.8 d 466.5 (lb l025.7 b

 

lColumns followed by the same letter are not significantly different (P=0.05)
according to the Student-Newman-Keuls Multiple Range Test.

2Applied at plant in the fertilizer furrow at a rate of 3.4 kg a.i.lha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha
on May I, I979.

67

DISCUSSION

The Role of Soil Nutrients and Nematicides on S. tuberosum and P. penetrans

The growth of 9. tuberosum is limited by numerous abiotic and biotic
factors. Many studies have demonstrated the importance of fertilizers in
promoting 9. tuberosum growth and optimization of tuber yield. Relatively
little, however, is known about the influence of E. 9e_netrans on growth,
development and yield of 9. tuberosum. Characterization of plant-nematode
interactions is dependent on accurate assessment of the influence of various
biotic md abiotic factors inherent in the nematode crop ecosystem and
associated production management strategies. Knowledge of preplant
nematode densities and the associated levels of control achieved with chemical
pesticides is needed to understmd the relationships governing fertilizer
recommendations and plant and yield response. The development of future 9.
tuberosum production practices is dependent on identifying these relations.

Subtle changes in the growth and development of 9. tuberosum associated
with N or P fertilizer were directly related to differences in final tuber yield.
Observations empirically derived showed that 9. tuberosum grown at increased
N or P levels accelerated early season foliar growth. This is partially reflected
in the higher early season root, plant and foliage fresh weights. Plants at the
higher rates of N and P also responded by an earlier abscission of the lower
leaves. The leaf canopy developed sooner and, because of an adequate water
md nutrient supply and a larger leaf system, were maintained longer md plant
senescence delayed. P appeared to delay plant senescence which is contrary to

what is commonly reported to occur (Harris, I978). The change in nutrient

68

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.m. .8 28.; Fee: 6.:

 

 

 

 

 

 

 

 

co mmuvowpmma 0:» one :mmogaw: eo move; omega we mucmzpe:_ .m mczmwm
0.36 93.0%.. 9.40544 405.200

D .

m

I.

u.

no

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U see. m.

mu

6

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m

_U :3»

 

 

 

 

 

 

 

 

 

69

supply thus had its greatest affect on plant development by influencing leaf
area and leaf area duration.

Vigorous early season foliar growth which occurred at the high levels of N
and P did not appear to delay the initiation and development of tubers.
Differences in the number and weights of tubers and the attainment of final
tuber yield are usually associated with differences in the phenological
development of the plant (Harris, I978; lvins and Milthorpe, I963). Fertilizers
exert their primary affect on yield by influencing the development and
maintenance of leaf area. A delay in plant maturity, which is usually seen in
plants which develop a larger leaf system during early developmental stages,
usually results in a delay in tuber initiation and development. These
observations of deviation from expected plant response to N and P may be
attributed to plant variability or sampling error. The lack of a phenological
response between N and P levels as they affect tuber development may have
resulted from high residual nutrient levels in the soil. Further research needs
to be conducted to elucidate these relationships.

The yield of 9. tuberosum to increasing rates of nitrogen and edaphic
pesticides was significantly increased. Yields increased with increasing levels
of nitrogen, attaining higher yields at the greater rates (Fig. 5). Tuber yields
also increased regardless of the pesticide used. Analysis of the I978 data
revealed that control of E. genetrans with either I,3-D 8 MIC or aldicarb
resulted in an increase in tuber set. Nitrogen then appeared to be limiting
yield. As the nitrogen rate was increased, the small tubers increased in size.
_P_. genetrans thus had its greatest affect on final yield in the alteration of the
nitrogen requirements of the potato plant for maximizing yield.

Due to the Bray P| soil test results, little or no crap response was

70

 

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72

expected from soil with such high levels of available phosphorus (over 268 kg
Bray soil phosphorus per hectare). Despite the high phosphorus residues in the
soil, yield responses were significant from increasing the phosphorus application
rate (Figs. 6, 7). Nelson and Hawkins (I947) have also reported significant yield
responses from additional phosphorus even on soils high in accumulated
phosphorus. It should be noted that other factors than 01 increase in final tuber
yield need to be examined to justify increasing fertilizer recommendations.
When cv Russet Burbank yields are examined, yield increases with increasing
phosphorus are partially offset by increasing yields of misshapen tubers. A cost
function taking into consideration fertilizer expense and an increase in
unmarketable tubers must be considered in the economics of future production
mmagement practices involving fertilizer use.

Control of E. genetrans in I979 did not appear to affect tuber set as it did
in I978, although significant yield increases did occur with edaphic pesticide
use. The number of smaller tubers were generally higher at the lower P levels
and increased in size with increasing P. The influence of E. genetrans on tuber
set may need to be examined more closely in relation to pesticide and fertilizer
use. Nematode control recommendations based on preplant population densities
are dependent on it.

The roles of fungal diseases were not evaluated in these tests. Certain
soil fumigants applied at specific rates control root diseases of 9. tuberosum
caused by fungi and plant parasitic nematodes (Cetas and Harrison, I963; Miller
and Hawkins, I969). In addition to the fungicidal and nematicidal properties,
many edaphic pesticides affect soil nutrient relations (Elliot e_t a_l., I977;
Winslow and Willis, I972). This may explain why yields increased with I,3-D 8
MIC even though control of E. genetrans did not appear to be achieved.

73

Knowledge of the population dynamics of E. genetrans md the associated
host response is essential to the understanding of how E. genetrans influences
plant growth and development. Assessing plant response and crop losses is
dependent on reliable methods of monitoring E. fletrans populations, host
plant responses and environmental factors which may modify these
relationships. Plant pathogenicity can be measured by examining the
deleterious affect of the abiotic or biotic factors on relative growth rate. In
other cases, it has been measured in terms of plant growth reductions expressed
by plant weight such as differences in root weight. It is questionable whether
the techniques employed in these studies are sensitive enough to accurately
measure and identify the small differences in plant growth (as expressed by
plant weight) occurring between treatments. This may be due to the error
involved in measuring plant biomass in units of plant fresh weight. It may also
explain why so few significant differences in any of the plant growth
parameters were observed during the season. The possibility does exist that
insignificant differences in plant growth and development as measured by plant
fresh weight can occur during the course of the season, additively culminating
with significant differences in tuber yield.

The data collected on the plant and root systems do support the view that
E. genetrans causes most of its damage by destroying or inhibiting the normal
physiological function of the root system, rather than by significantly reducing
root weight. This may explain the significant differences in yield with
increasing N and P levels. A healthy nematode-free root system is required for
optimal use of these elements and maximization of yield.

Plant response to nematode infection may also result in the formation of

new roots to compensate for the roots destroyed. Thus, slow growth early in

74

 

  

 

 

9 CV. SUPERIOR
‘3 e-
g "' CHECK
4.
:3 :3-
o ..
(D
‘- O
m 2-
2
C!
m
j.—
9 2‘
E 1-3.0+I‘IIC
a: S- /’/’M
_I
E m- r/ 31 FILDICFIRB
D N /B~ ,-/ \\
|-— / ‘x‘e,’ \0
a I I I I I
0 250 500 7in 1000 1250
nccun. DEGREE DRYSIBRSE 10 C)

 

 

 

Figure 8. Influence of two edaphic pesticides on total (soil + root)

population density of E, Benetrans on 9, tuberosum (cv
Superior) (1978).

75

 

     
   
 

 

 

 

g_ CV. SUPERIOR
A m
.—
O
a o
+ 3‘ ,
-' i\
D f
a, g_ 1" \ CHECK
U N '1' I \
g 1" \. 1-3.D+HIC
O 1'
CE ID-I ,'
a: —- i
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§ 4'"
1.1.1 8..
0. fl ’0'
a:
D— 1'
e ‘° e. .._...1" /
IS “""\-e”’ \o FILDICFIRB
.— o I I I I I I
0 250 500 750 1000 1250 1500
BCCUM- DEGREE DBYSIBRSE 10 C)

 

 

Figure 9. Influence of two edaphic pesticides on total (soil + root)
population density of E, penetrans on 9. tuberosum (cv
Superior) (1979).

76

 

2‘ CV. RUSSET BURBRNK
§- 4

  
 

 

 

i

1

I CHECK
l

l1-3.0+HIC

 

TOTHL P. PENETRRNS [SOIL+RO0T)

 

as
BLDICRRB

a I I I I I fiI
0 250 500 750 1000 ‘250 1500

 

 

RCCUH- DEGREE DRYSIBHSE 10 C]

 

Figure 10. Influence of two edaphic pesticides on the total (soil +
root) population density of E. penetrans on g. tuberosum
(cv Russet Burbank) (1979).

77

the season and a delay in plant maturity due to prolonged vegetative growth
may be mare indicative of _P_. penetrans pathogenicity. It may also be that the
initial soil and root population densities of E. penetrans observed in many of
these field studies were at levels that the plant could tolerate and thus caused
no detrimental affect on plant or root production. Differences in _S_. tuberosum
susceptibility to E. wetrans has been demonstrated by Bird (I977) and Bernard
md Laughlin (I976). Differences in varietal response of §. tuberosum to E.
fletrans may need to be examined more closely in relation to other biotic and
abiotic factors influencing plant growth, development md yield.

Chemical nematicides are used to reduce soil population densities of
nematodes below plant damage thresholds. It is difficult to ascertain whether
any of the nematicides used in these studies, with the exception of aldicarb,
reduced soil populations of E. wetrans below the damage thresholds
established for §. tuberosum in mineral soils. The concept of a universally
acceptable damage threshold for §. tuberosum needs to be modified to take into
consideration other factors such as Ferris (I980) has suggested. In light of the
present studies, the static models of the past need to be examined more closely
in relation to the influence of various abiotic and biotic factors on the dynamics
of plant damage thresholds.

Significant reductions in population levels of E. penetrans were achieved
with some of the edaphic pesticides evaluated in these studies. With the
exception of aldicarb, final soil and root population densities of E. penetrans
were higher than those observed at the beginning of the season (Figs. 8, 9, IO).
In some cases, as with I,3-D 81 MIC, a late season resurgence in population
densities of E. penetrans was statistically indistinguishable from the controls.

Only in the aldicarb-treated plots were final soil and root population levels

78

reduced below the initial population levels. The possibility of multi-year

nematode control with this material is being evaluated by Bird g a_l. (I980).
The efficacy of edaphic pesticides evaluated in these studies was

statistically insignificant in terms of nematode control because of considerable
variability in the number of E. penetrans recovered from soil and roots within
treatments. Variability in the rate and placement of edaphic pesticides may
have contributed significantly to the variability in the number of nematodes
observed. This could have contributed to the statistical insignificance declared
in the malysis of soil and root population densities of E. penetrans. This was
specially evident in the aldicarb treatments where abnormally large population
densities of E. wetrans occasionally occurred. Nematode sampling is mother
source of experimental error that may have contributed to count variability,
such as failing to obtain a representative soil or root sample from an underlying
aggregated population from the soil or roots. Further research into these areas
is therefore needed.

The linear relationship observed between the LO ml subsample and the
larger I0.0 ml sample showed that the subsample can be used to accurately and
reliably estimate both soil and root population densities of E. penetrans. As the
mean number of E. penetrans increased in the LO ml subsample, so did the
corresponding E. penetrans density observed in the I0.0 ml sample. The mean
population densities of E. penetrans were used to formulate the relationship
because seldom is one sample used to accurately estimate field population
densities of plant parasitic nematodes.

The economics of nematode sampling prohibit large numbers of samples
from being processed to estimate field population densities of most plant

parasitic nematodes. Due to the aggregational characteristics of nematode

79

populations in soil and roots, smaller numbers of samples can result in gross
errors of considerable magnitude toward estimating field population densities of
nematodes. Conversely, greater numbers of samples will usually provide more
accurate estimates of the true mean population density. Using the smaller
subsample can allow a greater number of samples to be used to estimate soil
and root densities of E. penetrans.
An examination of residuals of the individual observations showed that
over 80% of the total variability between density estimates of the LO ml
subsample and the I0.0 ml sample occurred when fewer thm 3.0 E. penetrans
were observed per I.O ml subsample. If economic or damage threshold densities
are small, as they are reported to be for E. metrans (< I0 per l0.0 ml sample),
the population estimates derived from the smaller I.0 ml subsample may be of
limited value. The relationship is applicable only to economic or damage
thresholds where nematode densities are greater than l4 per l0.0 ml sample.
At densities below this level, the subsample method cannot distinguish E.
pggetrans densities from zero. The technique may be more applicable to
another commodity or variety where economic or damage thresholds are higher.
An analysis of variance was conducted on plant data derived from the
following equation:
Y = 2(Xijk) / N
where: X = observed plant fresh weight
i = treatment number from I to i
j = block number I through]
k = sample period from I through k
'N = number of sample periods

Y = average season treatment mean

80

It was assumed that the time in which plant samples were taken from
each treatment will dictate to a major extent the quantitative level of the
mem seasonal fresh weight. Any random combination of plant samples taken
during the course of the season will produce a different mean seasonal fresh
weight. Depending on the plant parameter, a greater frequency of plant
samples occurring in the early stages of plant growth will bias the estimate and
reduce the value of the seasonal mean. In contrast, a greater sample frequency
during the later season when some plant parameters (e.g., tuber weight) are
developing at maximal rates, will tend to bias the estimate by inflating the
seasonal treatment mean. Unless a method is devised for weighting observation
times between and within seasons, 0 comparison between treatment effects is
difficult and has interpretational problems associated with it. If plants within
treatments are sampled synchronously through the season, comparison of
treatment effects can be made.

Temporal changes in the phenological development of g. tuberosum may
obscure differences between treatments. If a treatment produces a shift in
phenological development, treatment differences in seasonal fresh weight will
tend to be small and not significant (P=0.05). Collapsing time within
treatments will obscure these phenological relationships and declare
insignificmce between treatments. If, on the other hand, plant fresh weights
between treatments is observed to be consistently higher or lower through time,
then treatment differences are maximized in the final analysis and significance
(P=0.05) between treatments declared. The significance implied by the analysis
suggests that there are either significant shifts in the phenological development
of the plant and/or significant treatment responses. By collapsing time, the

cause of the differences is indistinguishable.

81

ROLE OF E. PENETRANS AND _I=. DECEMLINEATA
ON THE GROWTH OF _S_. TUBEROSUM

The objective of a study in I979 was to examine the affects of E.
wetrans and E. decemlineata on the growth, development and yield of §.
tuberosum (cv Superior). An additional objective was to examine how plant
defoliation by E. decemlineata, as it is mediated through §. tuberosum, affects

the population dynamics of E. penetrans.

82

MATERIALS AND METHODS

glged Environment

Seed pieces (cv Superior) wee planted on May 24, I979, at the Montcalm
Potato Research Farm in west central Michigan. Each plot consisted of two
rows, l.83 m in length md 0.86 m apart, with 0.20 m spacings between plants.

Twenty-seven insect cages, measuring l.83 x l.83 x l.83 m, were erected
over the plots after planting. Each cage was assigned one of nine different
treatments. A treatment consisted of one of three population levels of E.
decemlineata and one of three population levels of E. Be_r_1etrans. E.
decemlineata population levels were achieved by stapling leaves with egg
masses obtained from adjacent potato fields to the leaves of newly emerged
plants within the cages on June 22, I979. Eggs were allowed to hatch and then
larval populations manipulated to plant densities of either 0, ID or 20 larvae per
plant.

The nematode population levels of E. penetrans within the cage plots were
achieved by various techniques. Preplant sampling of the cage sites provided
estimates of initial soil population densities (Pi) of E. penetrans. Initial soil
population densities were then numerically ranked and separated into three
groups: low (2 i P; _<_ 4), medium (l5 _<_ P; i 25) and high (5| l _<_ P; _<_ 532). The
cages with the low initial soil population levels were then fumigated with I,3-D
(Telone II, 93.5 l/ha) on May I, I979. The medium population levels represent
natural field populations. The high population levels of E. penetrans were
achieved by complementing the natural field populations with a liquid

suspension of E. penetrans obtained from potato roots cultured in the

83

laboratory. A l0 ml aliqumt of the nematode suspension was applied at
planting to these treatments and represents an approximate addition of 500

nematodes to the root rhizosphere of the germinating potato plant.

Plant growth and development was monitored every 2-4 weeks throughout
the season. Plants were randomly selected from one specific row of each plot
during the season. After removal, plants were returned to the laboratory for
analysis. In the laboratory, root weight, stem weight, leaf weight, tuber weight
and tuber number were recorded for each sampling date. Plant dry weights
were then determined after drying at 35 C in a plant drying oven. Total leaf
area of each plant was calculated with a Lambda leaf area meter (Model Ll
3000).

Soil and root populations of E. penetrans were estimated by techniques
previously described. On September l4, I979, the remaining row within each
cage plot was harvested. Individual tubers from each cage plot were separated
into ten different tuber size categories (l-l0 cm). The number of tubers in
each size class were counted and weighed. During the season, plants were

maintained under normal commercial irrigation and disease control practices.

Path Coefficient Analysis

Path coefficient analysis was used as a conceptual framework and a guide
for data collection as well as a method for analyzing the results. It is a
technique, first proposed by Wright (l92l, I934), to deal with the
interrelationships among linearly related variables. Statistical applications of
the path coefficient method have been demonstrated by Li (I977), Duncan
(I966), Grafius (I978) and Tai (I975). Its application to the investigation of

plant stress caused by insect and nematode pests is unique.

.m_ampge> gmguocm Co meoouao as» m=P=_ELmume cp genome pmzewmme
emewmpaxmea cm can mm_nmwem> pewecmeou ecu “cavemamecp couzumn a_smcopum_mm

 

.HH me=m_a
m0h0<m m0._.0<u_
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133mm“

 

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85

uncontrolled
environmental
factors

         

 

fa =!II:‘

.v\*‘.‘-J

awe.»-

 

TUBER TUBER
INITIATION PHASE GROWTH PHASE

 

YIELDanER N0 XWT TIE/ER]

Figure 12. Conceptual diagram illustrating sequential effects of

abiotic and biotic factors on yield components of
_S_. tuberosum.

 

 

E f; \
”AL/Z ,w

Figure 13. Path diagram of path coefficient analysis for
_S_. tuberosum ontogeny.

87

Path coefficient analysis is a form of structural linear regression malysis
with respect to standardized variables in a closed system. Unlike multiple
regression, the path method is not concerned with the best or closest prediction
of Y based on the information contained in the X variables. It is concerned
with the proposal of a plausible interpretation of the interrelationships between
variables. It is based on the construction of a qualitative diagram in which
every component of the system is represented either as being completely
determined by individual components within the system as is A (Fig. l I) or by
combinations of individual components as in B. The variables are arranged in a
proposed causal order to indicate their interrelationships. Directions are
assigned via arrows to indicate the influence each variable has on mother. A
double-headed arrow is used to denote a mutual association between variables.
In this way, the direct md indirect influences certain causal components have
in producing changes in other components can be illustrated.

The path diagram is based on the sequential development of the yield
components of the potato plant (Fig. I2). Final yield in the diagram is
determined by the sequential affects the various abiotic and biotic factors have
on the yield components at their respective developmental stages. For
example, the development of the first yield component, number of tubers per
plant, is completely determined by the resources available to the plant during
the early stages of growth and the number and frequency of pests attacking it.
Another yield component, average tuber weight per plant, whose development
occurs after tubers are initiated, is not only influenced by the resources
available to it during its growth phase but also by the initiation and
development of tubers which occurred earlier. Within this sequential

arrangement, final yield is the multiplicative product of average tuber number

88

per plant did the average tuber weight per plant.

The plant environment has been separated into two independent
components. First, a biotic component which includes a foliar feeding
component in E. decemlineata and root-feeding component in E. penetrans. All
the other environmental factors affecting the plant during its ontogeny are
pooled together to form the uncontrolled environmental components, U|
through U7. These would include such factors as genetic variability, undetected
environmental and pathological factors and experimental error. These also
represent the residual effect of the variation that has been left unexplained by
changes in the causal variables on the effect variable.

A path coefficient analysis of the causal diagram was used to determine
the interrelationships between biotic factors, yield components and yield (Fig.
l2). Each path in the diagram not only has a direction but also has a
quantitative value to measure the importance of a given path of influence. The
value assigned to the path is the path coefficient Pi] (e.g., ny is the path from
X to Y). Each path coefficient deals with the relationships between
stmdardized variables. Standardized variables are those variables measured
from their mean values in units of their own standard deviation. The process of
stmdardization makes all variables equal in mem (zero) and equal in variance
(unity).

The path coefficient measures the importance of a given path of influence
from the cause to the effect variable. It is defined as the proportion of the
variability explained by the causal variable when all other factors are held
constant except the one in question, the variability of which is kept unchanged
to the total variability. Variability is measured by the standard deviation.

Each path coefficient is calculated according to the specified structure of the

89

“here:

'12 ' P12
TuTTuT’ufis
'n'TuT’ufii
'53 ' ’s:

'55 ' ’56

:7I ; ’7!'+ P62r76 -—-uhorerr6xfr7x- 0

’37 ' '31

rt! - ,3! -uhoro rsxfrTx- 0

'w ' Tm

'11: ' ’10 T ’u’w T ’u’xw T '39’23’12 T '12’2x’xx’w
’20 ' '20 T 1'2111’101 T '31:”23 T ’zx’u’w

rxu - PX" + PXYPYU

‘3" ' '39 T 'n'w T '3x’xw T 1'zw'n T Pax’xv’w
Tm ' 'su T ’u’w T ’ax’xw T ’43’23'211 T ’63’ 313x150

51: T ‘3er T Psapsr’w T 1’sa‘fiapm

r
' ’61: T ’sr’w T ”7096
r

711 T 'n’w T ’60'75

Tau " ’31: T ’sr’w T Pat’n’w T ’07’75’51:
Tar " ’81 T ’07’ 71 T '37’76'6!
’51: T 'ss’sr T ’56'76’7:

- P + P P

11: 12
’1: ' ’1! T ’19:! T P12"218’10: T 1’12""23"31r
" ’2! T P2x130: T 1’31’23 ,

- P3Y + PJXPXY + szr23

21: T '12'23’31:

" '51: T 'as’n T ’53? 311910: T ’43'23’22.

”ax " 1’11: T 15.3%): T Pafzs'zx

Figure 14. Path coefficient equations.

No. of Tubers] Plant

2 2
Prx {1 T sz 'Pax ' 2P2x’3x'23
Degree of Determination - 1 - Pr;

 

 

Average Tuber wt. I Plant ( Y )

2 2 2 '
PrY. ‘5 ' Par " P10: " P72 " _zpsrpxrrax " ZPGYP7YT76 21’xsr"7x"7x

Degree of Determination ' 1 - Pr:

 

Yield ( w )
_ 2
Prw \fi ' PW
2

Degree of Determination a 1 --Prw

 

Figure 15. Coefficients of determination.

91

proposed relationship. For simple cases where one independent and dependent
variable are involved (Fig. IIA), the regression coefficient (Bxy) for the
stmdardized variable and correlation coefficient (rxy) are both equivalent to

the path coefficient ny. Thus:

PXY = rxy = Bx). where Bx). = bx). (sx)/(sy)
In this simple case, the simple linear regression coefficient can be transformed
into the standardized regression coefficient by the process indicated above,
where bx). is the simple linear regression coefficient, sx is the standard
deviation of x, and s). is the standard deviation of y.

For uncorrelated causes involving multiple independent variables, the path
correlation coefficient is no longer simply the corresponding correlation
coefficient (Fig. I IB). Li (I975) has provided a more comprehensive description
of the formulas and their derivations required to calculate path coefficients
between uncorrelated and correlated causal variables. A summary of the
equations used in the calculation of the path coefficients and coefficients of

determination are listed for quick reference (Fig. Ill, IS).

Solanum tuberosum Agroecosystem

A non-caged open field experiment was conducted in I979 to examine the
influence of E. decemlineata, E. wetrans and nitrogen fertilization on the
growth of S. tuberosum. Seed pieces of cv Superior were planted on May l7,
I979, at the Montcalm Potato Research Farm. Each plot consisted of four rows
l5.24 m in length and 0.86 m apart, with 20.5 to 30.5 spacings between plants.
The plots were arranged in a completely random block-three factorial
experimental design with each treatment replicated five times.

A treatment consisted of either of two levels of NPK fertilizer (0 and 560

92

kg/ha, NPK 20-l0-l0), and one of two levels of nematicide (I,3-D + MIC,

broadcast at 93.5 l/ha (Table I4). Plots treated with I,3-D + MIC were injected
to a l5 to 20 cm soil depth on May I, I979. Those plots to receive fertilizer

were also side-dressed during hilling at an application rate of l62.5 kg/ha urea
(45% N) on June 22, I979. Insect control programs were initiated at various
times during the season to achieve three levels of plant defoliation (no
defoliation, early-season defoliation and full-season defoliation). Within the no
defoliation plots, foliar applications of methamidophos (Monitor IOG; 3.4 kg/ha
active ingredient) were applied as needed for E. decemlineata control. An
insect control program was not initiated until flowering within the early-season
defoliation plots. F ull-season defoliation plots remained untreated.

Plant growth and development was monitored at various intervals
throughout the season. This was accomplished by randomly selecting two plants
from the outside rows of each plot and returning them to the laboratory for
malysis. In the laboratory, root weight, foliage weight md tuber weight and
number were recorded for each sampling data. Soil and root population
densities of E. penetrans were estimated from samples taken at these times
according to techniques previously described. At harvest, the center two rows
of each plot were harvested, graded and weighed. All plots were irrigated with
a solid set sprinkler system according to need determined by measurements of

evapotranspiration.

93

Table I4. I979 Insect-nematode potato agroecosystem study treatments.

 

 

Defoliation Level Nitrogen (kg/ha) Fumigation (l/ha)
None:3 0 0
seal 0
o 93.52
560 93.5
Early-season 0 0
560 0
0 93.5
560 93.5
Late—season 0 0
560 0
0 93.5
560 93.5

 

lNitrogen fertilizer (NPK 20-l0-l0) applied at planting, plus l62.5 kg/ha Urea
(45% N) at hilling on June 22, I979.

2Telone ll broadcast injected‘to a 20 cm soil depth on May I, I979.

3Foliar applications of Methamidophos IOG; 3.4 kg/ha a.i. as needed for E.
decemlineata control.

ca wwA“ .

94

RESULTS

Egggd Environment

Larval feeding by E. decemlineata influenced the population dynamics of
E. penetrans and the growth and development of _S_. tuberosum. The direct
effect of E. decemlineata was a significant (P=0.05) reduction in leaf dry
weight md leaf surface area, which increased with increasing plant density of
E. decemlineata (Tables l5 and I6, respectively). This relationship was evident
season-long, but only significant (P=0.05)‘ during the second plant sample
(DD|0C=668.3) for leaf dry weight and during the final two plant samples
(DDloc=668.3 md 954.l) for leaf surface area. As E. decemlineata reduced

 

leaf dry weight and leaf surface area, there was a corresponding reduction in
plant root dry weight (Table U), which was significantly (P=0.05) higher in the
beetle-free plots during the final plant sample (DD|0C=9S4.I). These changes
are directly reflected in the significant (P=0.05) reductions in plant and tuber
dry weights during the later stages of plant growth for the beetle-infested
treatments (Tables I8 and I9, respectively). It was not until the final plant

sample (DD|0C=9S4.I) that E. decemlineata significantly (P=0.05) reduced the

 

number of tubers per plant (Table 20). Tuber numbers were always higher for

the entire season in the beetle-free treatments. E. decemlineata had no

 

significant (P=0.05) influence on stem or stolon dry weight season-long (Tables
2| and 22, respectively).

I E. penetrans directly influenced the growth and development of _S_.
tuberosum. E. penetrans significantly (P=0.05) increased leaf dry weight at the
low initial soil population level during the first plant sampling (Table l5). Leaf

dry weights were consistently higher at the lower P; for the remainder of the .

95

 

 

 

 

 

 

Table I5. Influence of three inoculated densities of P. enetrans and three
plant densities of E. decemlineata on leafary weight of §.
tuberosum (cv Superior).

Treatment Leaf dry weight (Grams)l
_1_._. decemlineataz 1_=>_. penetrans3 511.2 668.3 954.1
0 Low 6.66 c4 19.05 b 27.17 a
0 Medium 3.73 ab l2.00 ab I9.47 a
0 High 3.36 ab l4. l3 ab 27.57 0
l0 Low 5.l7bc 7.3l ab l8.500

l0 Medium 2.32 ab l0.3l ab 25.87 a

l0 High 3.47 ab 5.05 a 5.73 a

20 Low 4.84 abc 9.59 ab l2. 63 a

20 Medium 2.35 ab 4.45 a 7.57 a

20 High l.8l a 3.56 0 l3. I7 a

0 4.45 a l3.85 b 23.25 0

l0 3.700 8.l4a l7.55a

20 3.00 a 5.87 a I I. l2 a

Low 5.56 b l l.98 a I9.43 a
Medium 2.80 a 8.92 a I7.63 a
High l 2.88 a 7.58 a I5.49 a

 

IDegree day accumulation base I0 C.

2Maintained plant density of E. decemlineata of 0 per plant from emergence to
harvest.

3Initial population density level of E. penetrans established of planting.

4Columns followed by the same letter are not significantly different (P=0.05)
according to the Student-Newman-Keuls Multiple Range Test.

96

 

 

 

 

 

 

Table I6. Influence of three inoculated densities of E. enetrans md three
plant densities of E. decemlineata on leaf area of _5. tuberosum (cv
Superior).
Treatment Leaf area (cmz)l
E decemlineataz E- Egetrans3 514.2 668.3 954.1
0 Low 2919.3 c4 7l84.9b 2221.1 b
0 Medium l742.0 abc 38 l 2.3 a 382.8 ab
0 High l770.9 abc 3967.3 0 933.6 ab
l 0 Low 2590.5 c l948.4 a 397.8 ab
l0 Medium 967.4 0 3026.9 0 743.2 ab
l0 High l097.0 ab l268.9 a 77.7 a
20 Low l88l.7 ab 2305.8 a 306.I ab
20 Medium ”22.3 ab l3l5.4 0 2| L9 0
20 High 687.9 a 798.8 a 74.4 a
0 2049.3 0 4545.9 b I084.6 b
l0 I596.4 0 2270.9 0 427.9 a
20 l230.6 a l473.3 a l97.5 a
Low 2463.8 b 38 l 3.0 a 975.0 a
Medium l277.6 a 27 I8.2 a 446.0 a
High l l85.2 a 20--.7 o 36 L9 a

 

lDegree day accumulation base l0 C.

2Maintained plant density of E. decemlineata of 0 per plant from emergence to

harvest.

3Initial population density level of E. penetrans established at planting.

“Columns followed by the same letter are not significantly different (P=0.05)

according to the Student-Newman-Keuls Multiple Range Test.

97

Table I7. Influence of three inoculated densities of E. penetrans md three
plant densities of L. decemlineata on root dry weig t of §. tuber-
osum (cv Superiorf

 

 

 

 

 

Treatment Root dry weight (Grams)l

E. decemlineataz E- metrans3 514.2 668.3 954.1
0 Low 0.44 6‘1 1.121: 1.006
0 Medium 0.3I a 0.60 ab 0.37 a
0 High 0.30 a 0.65 ab 0.90 a
I0 Low 0.3l a 0.32 a 0.27 a
l0 Medium 0. l 9 a 0.69 a 0.77 a _
l0 High 0.32 a 0.49 ab 0.23 a
20 Low 0.35 a 0.75 ab 0.27 a
20 Medium 0.24 a 0.50 ab 0. ID a
20 High 0. l8 0 0.l5 a 0.0l a
0 0 37 a 0.76 a 0 75 a
l0 0 24 a 0.50 a 0.39 ab
20 0 26 a 0.47 a 0 28 a

Low 0.37 a 0.73 a 0.5l a

Medium 0.24 o 0.60 a 0.5I a

High 0.27 a 0.43 a 0.42 a

 

IDegree day accumulation base I0 C.

2Maintained plant density of E. decemlineata of 0 per plant from emergence to
harvest.

3Initial population density level of E. metrans established at planting.

“Columns followed by the same letter are not significantly different (P=0.05)
according to the Student-Newman-Keuls Multiple Range Test.

Table l8.

98

Influence of three inoculated densities of E.
plant densities of L. decemlineata on plant dry weig t of §. tuber-
osum (cv Superior).-

etrans md three

pen

 

Treatment

 

 

Plant dry weight (Grams)l

 

 

E. decemlineataz 3. 22811111183 514.2 668.3 954.1 1 177.0
0 Low 16.28 154 81.32 b 154.43 b 1 12.90 a
0 Medium 7.97 a 46.87 ab 108.83 a 69.01 a
0 High 8. I 3 a 50.55 ab l35.83 a 90.36 a
10 Low 14.80 b 29.30 a 1 17.13 a 58.82 a
l0 Medium 5.64 a 3 I.26 a I20.83 a 36. l 9 a
10 High 7.69 a 18.96 a 52.33 a 9.91 a
20 Low 12.25 ab 54.1 1 ob 83.07 a 46.87 a
20 Medium 6.25 a 21.71 a 47.63 a 38.12 a
20 High 5.27 a 10.04 a 62.97 a 18.75 a
0 10.60 a 55.22 a 127.86 b 82.89 b
10 9.44 27.82 a 98.70 ab 37.84 a
20 7.92 a 28.62 a 64.56 a 34.58 a
Low 14.45 b 54.91 b 1 18.21 a 72.86 a
Medium 6.62 a 33.28 ab 92.43 a 47.77 a
High 7.03 a 25.52 a 83.7I a 39.67 a

 

IDegree day accumulation base I0 C.

2Maintained plant density of E. decemlineata of 0 per plant from emergence to

harvest.

3Initial population density level of E. penetrans established at planting.

“Columns followed by the same letter are not significantly different (P=0.05)
according to the Student-Newman-Keuls Multiple Range Test.

99

Table I9. Influence of three inoculated densities of E. penetrans and three
plant densities of L. decemlineata on tuber dry weig t of _S_. tuber-

osum (cv Superior).-

 

Treatment Tuber dry weight (Grams)I

 

 

 

 

1:. decemlineataz g. geneirdns3 514.2 668.3 954.1 1 177.0
0 Low 0.68 64 40.1015 110.13 a ”2.900

0 Medium 0.01 a 22.57 Ob 77.13 a 69.0l d

0 High ' 0.01 a 23.77 Ob 91.00 a 90.36 a

10 Low 2.76 d 13.60 ab 83.93 0 58.82 0
l0 Medium 0.00 a 7.77 a 76.90 a 36. l 9 a
10 High 0.05 a 6.17 d 40.20 a 9.91 a
20 Low 1.71 d 28.36 Clb 59.07 a 46.87 a
20 Medium 0.01 a 7.97 d 30.63 a 38.12 a
20 High 0.02 a 0.62 a 40.27 0 I875 a
0 0.22 d 26.66 b 89.72 b 82.89 b

10 1.04 a 9.42 d 67.59 ab 37.84 a

20 0.58 a I2.32 a 43.54 a 34.58 a
Low 1.72 b 27.35 b 84.60 0 72.86 a

Medium 0.01 a 12.77 a 61.56 a 47.77 a

High 0.03 0 I0. I 9 a 57. I6 0 39.67 a

 

lDegree day accumulation base l0 C.

2Maintained plant density of E. decemlineata of 0 per plant from emergence to

harvest.

3lnitial population density level of E. wetrans established at planting.

 

4Columns followed by the same letter are not significantly different (P=0.05)

according to the Student-Newman-Keuls Multiple Range Test.

100

Table 20. Influence of three inoculated densities of E. penetrans and three
plant densities of E. decemlineata on tuber num er per plant of §.

tuberosum (cv Superior).

 

Treatment Tuber number per plantl

 

 

 

 

E. decemlineataz g. metrans3 514.2 668.3 954.1 1 177.0
0 Low 15.7 be“ 47.3 (lb 13.7 a 17.3 b
0 Medium 6.0 abc 25.0 ab l2.3 a I2.7 ab
0 High 7.0 abc 30.0 ab l0.0 a l0.7 ab
l0 Low l8.3 c l7.7 ab I3.0 a 7.0 a
l0 Medium 0.3 a I6.7 ab l2.3 a 8.0 0
l0 High 5.7 abc 23.0 ab 6.7 a 4.0 a
20 Low l2 7 abc 52.7 b 9.7 a ”.0 ab
20 Medium 5.0 abc 2 I.7 ab l l.3 a 7.0 a
20 High 3.0 ab l0.3 ab 8.7 a 5.0 a
0 l0.l a 33.6a ll.7a I2.8b
l0 7.3 a I7.9 a l0.9 a 6.4 a
20 6.9 a 28.2 a 9.9 a 7.7 a

Low l5.6 b 39.2 a I2.l a II.8 a
Medium 3.8 a 2|.I a l2.0 a 9.2 a
High 5.2 a 2|.I a 8.4 a 6.6 a

 

IDegree day accumulation base l0 C.

2Maintained plant density of E. decemlineata of 0 per plant from emergence to

harvest.

3Initial population density level of E. penetrans established at planting.

 

“Columns followed by the same letter are not significantly different (P=0.05)

according to the Student-Newman-Keuls Multiple Range Test.

101

Table 2 l. Influence of three inoculated densities of E. penetrans md three
plant densities of L. decemlineata on stem dry weig t of §. tuber-

osum (cv Superior).-

 

Treatment Stem dry weight (Grams)l

 

 

 

 

1: .decemlineataz E. ge_neirdns3 514.2 668.3 954.1
0 Low 6.76 64 17.37 b 13.67 a
0 Medium 2.98 a 9.55 ab 9. I3 a
0 High 3.17 d 10.06 db 13.33 6
l0 Low 5.95 a 6.58 a I2. l3 a
I0 Medium 2.35 a I0.20 ab I4.47 0
l0 High 2.78 a 5.57 a 5.20 a
20 Low 3.88 d 12.97 ab 8.93 O
20 Medium 2.5l a 6.80 a 7.67 a
20 High 2.42 a 4.57 a 8.00 d
0 4.24 d 11.50 Cl 11.52 a
10 3.32 a 7.87 a 1 1.08 a
20 2.94 a 8.1 1 a 8.02 a

Low 5.20 b 12.30 b 1 1.58 a
Medium 2.62 d 8.85 ab 10.42 a
High 2.79 a 6.73 a 8.84 O

 

lDegree day accumulation base l0 C.

2Maintained plant density of E. decemlineata of 0 per plant from emergence to

3

harvest.

Initial population density level of E. penetrans established at planting.

“Columns followed by the same letter are not significantly different (P=0.05)

according to the Student-Newman-Keuls Multiple Range Test.

102

 

 

 

 

 

 

Table 22. Influence of three inoculated densities of E. enetrans and three
plant densities of L. decemlineata on stolon y weig t of §. tuber-
osum (cv Superior).-

Treatment Stolon dry weight (Grams)l
E. decemlineataz E- Metransz‘l 514.2 668.3 954.1
0 Low 1.75 154 3.68 b 3.13 a
0 Medium 0.94 a 2. l 5 a 2.73 a
0 High I.29 ab l.94 a 3.03 a

I0 Low I.60 ab L49 0 2.30 a

l0 Medium 0.78 a 2.29 a 2.83 a

I0 High I.07 ab l.84 a 0.97 a

20 Low I.47 ab 2.44 a I.50 a

20 Medium I.l3 ab l.99 a l.37 a

20 High 0.83 a I. l3 0 L40 0

0 L32 a 2.46 a 2.62 a
I0 I I40 l.89a 2.l0a
20 llSa l.850 I42a
Low I.6I b 2.54 a 2.09 a
Medium 0.95 a 2. l4 ab 2.3I a
High I.06 a l.58 b L80 0

 

lDegree day accumulation base l0 C.

2Maintained plant density of E. decemlineata of 0 per plant from emergence to
harvest.

3lnitial population density level of E. penetrans established at planting.

4Columns followed by the same letter are not significantly different (P=0.05)
according to the Student-Newman-Keuls Multiple Range Test.

103

 

 

 

 

 

 

8—
0 LOW
A MEDIUM
34 eHIGH
CK
33
:31“
D
Z
(Z
LiJ-I
m0
3
.—
°01F2 a 4 5'6 7 8 910
TUBER SIZE CLRSS (CM)

 

Figure 16. The influence of three initial population levels of
E, enetrans on the average number of tubers in each
of ten different tuber size categories of §, tuberosum
at harvest.

104

 

   

 

 

 

 

°_ CPB/PLRNT
N
'1 III NONE
A 10
(Du 0 20
m
g
293‘ I
D
Z
x
LIJ .1
mm
D
.—
"01'2'3r 4r sr 8T '7T 8 e_o
TUBER SIZE CLFISS (CI‘II

 

Figure 17. The influence of three plant densities of _l___. decemlineata
on the average tuber number in each of ten different tUber

size categories 0f’§, tuberosum at harvest.

105

season. These same trends are evident when the influence of E. penetrans on
leaf surface area is examined (Table I6). No significant (P=0.05) differences in
root dry weight among E. penetrans levels were detected (Table I7). Tuber dry
weight was significantly (P=0.05) higher at the low initial soil population level
of E. metrans during the first two sampling periods (Table I9). Tuber dry
weight was always lower at the two highest Pi's of E. penetrans. Stolon, stem
and total plant dry weight responded similarly to E. penetrans (Tables 22, 2|
md I8, respectively). Dry weight significantly (P=0.05) decreased in these
parameters at the higher pi's of E. penetrans during the initial plant sample.
Significant (P=0.05) reductions in the number of tubers formed per plant were
evident during the initial plant sample (Table 20). Over four times as many
tubers were formed at the lower population level of E. penetrans than at the
higher population levels. I

Both E. decemlineata and E. penetrans affect final tuber yield, with E.
decemlineata having the only significant (P=0.05) impact in determining final
tuber yield (Table 23). Final yield of §. tuberosum decreased with increasing E.
decemlineata and E. penetrans population levels.

When final tuber yield is examined according to tuber size class, the
influence of E. penetrans and E. decemlineata on the yield components, tuber
weight and number per class, can be more closely scrutinized. The affect of
low initial soil populations of E. penetrans on the number of tubers per size
class was to significantly (P=0.05) increase the number of tubers in the smallest
observed tuber size category (Fig. l6). No other significant (P=0.05)
differences in tuber number were detected among the remaining tuber size
classes. E. decemlineata also had a significant (P=0.05) influence on the

number of tubers per tuber size class (Fig. l7). Increasing plant densities of E.

106

Table 23. Influence of three inoculated densities of E. %enetrans and three

plant densities of E. decemlineata on final tu er yiel of §_. tuber-
osum (cv Superior).

 

 

 

 

 

Treatment
Yield (grams/ l.83 m row)
E. decemlineata2 E. penetrans3
0 Low 4403.0 154
0 Medium 3 I 52.4 ab
0 High 3257.8 ab
I0 Low 235I.9 a
I0 Medium 2205.4 a
l0 High l704.6 a
20 Low l586.l a
20 Medium l l63.3 a
20 High l l08.7 a
0 3604.4 c
l0 2087.3 b
20 I292.0 a
Low 2780.3 a
Medium 2 I 73.7 a
High 2023.7 a

 

lDegree day accumulation base l0 C.

2Maintained plant density of E. decemlineata of 0 per plant from emergence to
harvest“

3lnitial population density level of E. penetrans established at planting.

“Columns followed by the same letter are not significantly different (P=0.05)
according to the Student-Newman-Keuls Multiple Range Test.

107

 

 

 

 

Q
§. 011.011
1A HEDIUH
0 HIGH
O
“3‘
(D
I:
C:
a:
8g-
5—
1':
5:3
“JO
5:53-
a:
U
(D
D
l—o
O—
N
°0 1I 2 3 4 are 7r8l910
TUBER SIZE CLRSS (CHI

 

 

 

Figure 18. Influence of three initial populations of P. enetrans
on mean tuber class weight in each of ten Hifgerent tuber

size categories of'§, tuberosum at harvest.

108

 

TUBER HEIGflT (ORBNS)

 

CPB/PLRNT
I3 NONE
48 10
€> 20

 

 

 

I T r I T
3 4 5 8 7 8 9 10
TUBER SIZE CLRSS (CH)

 

Figure 19. Influence of three plant densities of E, decemlineata on
mean tuber class weight in each of ten different tuber
Size categories of §, tuberosum at harvest.

 

109

decemlineata, from 0 to 20 beetles per plant, shifted a greater number of
tubers into the smaller tuber size categories and significantly (P=0.05) reduced
the number of tubers per tuber size class. The same type of kurtotic trends cm
also be observed in the mean tuber weight distribution between tuber size
classes for final tuber yield (l.83 m row) (Figs. I8 and I9). E. penetrans had no
significant (P=0.05) influence on final tuber weight distribution among tuber
size classes (Fig. l8), although differences are consistently lower in the high
initial soil population levels of E. penetrans when compared to the low initial
soil population levels. A mem tuber class weight shift among tuber size classes ,
is even moe evident when the effects of E. decemlineata are examined (Fig.
I9). Not only is total tuber weight significantly (P=0.05) reduced among E.
decemlineata plant densities, but also a greater proportion of the total weight
is shifted to the larger tuber size classes as E. decemlineata densities increase.

E. decemlineata feeding had no significant influence on soil population
densities of E. wetrans season-long (Table 24). Significant (P=0.05)
differences in the initial (DD|0C=34.9) population levels of E. penetrans were
evident. Root population densities of E. penetrans were significantly (P=0.05)
higher in plants maintained beetle-free during the latter part of the season

(DDioC=954. I)(Table 25).

PATH ANALYSIS

Correlation between yield and tuber number or average tuber weight was
positive and highly significant (P=0.0I, Table 26). Simple correlations between
yield and root weight, leaf weight and leaf area were always positive and highly
significant (P=0.0l, Table 26), with the strength of the association increasing

with time. Correlating final tuber yield with E. decemlineata resulted in a

Table 24.

110

tion densities of E. penetrans.

Influence of three plant densities of E. decemlineata on soil popula-

 

Treatment

E. Eenetrans per I00 cm3 soil I

 

 

 

E- decemlineataz 34.9 171.9 514.9 668.3 954.1 1217.5
E. penetrans3
0 Low 26.0 6154 1.6 a 6.3 a 10.7 a 26.3 ab 22.3 0
0 Medium 55.0 ab 25.0 bc 30.7 a 24.3 a l04.0 b 59.7 a
0 High 92.3 c 3 I.7 c l6.3 a 22.7 a 54.0 ab 40.7 a
I0 Low 22.3 ab 3.7 a 9.0 a 9.7 a I5.7 a l4.3 a
l0 Medium 48.7 abc l4.3 ab 30.7 b 25.7 a 86.0 ab 34.0 a
I0 High 68.0 bc l5.7 a I 5.7 a 35.7 b 60.0 ab 4I.7 a
20 Low lI.7a 3.7 a l0.0a l2.0a l|.0a l0.0a
20 Medium 57.0 a l6.3 ab 25.3 a 3 I.7 a 43.3 ab 40.0 a
20 High 65.7 bc | l.3 ab l2.7 a ‘ l7.7 a 70.7 ab 36.0 a
0 56.3 a I9.4 a I7.3 a 23.0 a 62.0 a 40.9 a
I0 46.8 a I2.3 a I9.l a l9.5 a 52.0 a 30.0 a
20 44.8 a l0.4 a l6.0 a 20.4 a 4I.7 a 28.8 a
Low 20.0 a 3.I a 8.4 a l0.8 a l7.7 a l5.6 a
Medium 53.6 b l 8.6 b 28.9 b 27.2 b 77.8 b 44.7 b
High 75.3 c l9.6 b l4.9 o 25.3 b 6|.6 b 39.4 b

 

lDegree day accumulation base l0 C.

2Maintained plant density of E. decemlineata of 0 per plant from emergence to

harvest.

3Initial population density level of E. wetrans established at planting.

1.

according to the Student-Newman-Keuls Multiple Range Test.

Columns followed by the same letter are not significantly different (P=0.05)

Table 25.

111

Influence of three plant densities of E. decemlineata on the root
population density of E. @etrans.

 

Treatment

 

 

E. penetrans per gram of root tissueI

 

 

1:. decemlineataz E- geneimns3 514.2 668.3 954.1 1217.5
0 Low 10.0 d4 17.3 a 104.3 0 34.7 d
0 Medium 6|.7 a 93.3 a 370.7 b l3.7 a
0 High 71.7 b 171.3 b 94.3 a 43.0 a
10 Low 25.7 d 24.3 a 108.3 a 16.7 CI
10 Medium 39.0 d 73.3 a 126.0 d 89.7 b
10 High 26.3 0 1 12.3 d 50.7 a 16.3 d
20 Low 34.3 a 56.7 a l5.0 a 20.3 a
20 Medium 26.3 a 149.3 a 66.7 d 1 1.0 a
20 high ‘ 53.7 a 93.3 0 52.0 0 18.0 0
0 46.5 a 102.9 0 189.8 b 28.8 a
10 29.8 a 55.9 d 94.8 a 44.3 d
20 38.1 d 99.8 a 44.6 0 16.4 a

Low 23.3 d 32.8 0 75.9 d 23.9 a
Medium 42.3 a 105.3 b 187.8 (I 38.l a
High 50.6 a 125.7 b 65.7 a 25.8 a

 

IDegree day accumulation base I0 C.

2Maintained plant density of E. decemlineata of 0 per plant from emergence to

3Initial population density level of E. penetrans established at planting.

harvest.

“Columns followed by the same letter are not significantly different (P=0.05)

according to the Student-Newman-Keuls Multiple Range Test.

112

Table 26. Simple correlation coefficients between E. penetrans and E.
decemlineata and yield of _S_. tuberosum.

 

Yield (l.83 M row)

 

Tuber initiation

Leaf weight] .5084I**
Root weight I .2932 6 * *
Tuber number .I 7240**

Tuber bulking phase

 

 

Leaf weight .52749**
Root weight .67337**
Average tuber wt.3 .472l7**
E. decemlineata -.Sl37 l **
E. penetrans
Soil I -.09496
Rootl -. l0077
Total 1 -. I2366
Soil3 -.05763
Root3 . l 8678
Total 3 . I4720

 

* Significantly different from r=0 at the 5% level

** Significantly different from r=0 at the I% level

113

43.7.83 >3 533.83 ..w. co

e_mpx eons» Peewm meeoemzpwew mueweoasoo we“ co mpmapaca peowoweeooo game .om acumen

 

 

 

cam; T

g d me..o.......o.e..q.a w
33.... 83...
22.3 22.3
.2... .82
01...... 32.... 88.... :3...
Bee... 3.. . 2.53.2.5
22.; A 2...... A .8...
«2...... .33.. 95.... :33. oz 58.... 3......
mean ... $3...
2%.... ......e...
.2... ......
3%.... 0...». .6.

 

285.68... ...

 

6.8358... n.

114

highly significant (P=0.0l) relationship and continued when E. decemlineata was

 

correlated with any other yield component such as leaf weight, leaf area, tuber
number, tuber weight, plant weight md stem weight (Table 26). The strength of
this association increased with each successive sampling data. Highly
significant (P=0.0l) negative correlations of E. penetrans with these same
parameters occurred mainly during the early stages of plant growth. As the
season progressed, these same correlations decreased and changed sign. Only
leaf weight and leaf area were significantly correlated with soil populations of
E. metrans and average tuber weight with root populations of E. penetrans.
Both soil and root populations were only weakly negatively correlated with final
tuber yield (Table 27). The degree of linear correlation between root population
md yield not only changed sign, but the strength of the association increased.

Simple correlation coefficients between E. decemlineata and E.
penetrans, including both soil and root populations, were negative and increased
' in value with time (Table 28).

Path coefficients were calculated according to the interrelationships
between variables proposed in the path diagram. These results are represented
in Figure 20. In the diagram, both leaf weight and the uncontrolled
environmental effect are the most important components occurring during the
early stages of plant growth with path coefficients of 0.5369 and 0.655l,
respectively. This explains 86% of the total variability in the number of tubers
initially formed. Changes in root weight explain only 8% of the total variability
in the number of tubers formed per plant. The remaining 6% of the variability
in tuber number per plant is explained by the interrelationship between leaf and
root weight.

During the tuber growth phase, both the leaf and uncontrolled

Table 27.

Simple correlation coefficients between E. Eenetrans and E.
rosum.

decemlineata and yield components of S. tu

 

E. decemlineata

Tuber Initiation Phase

 

Leaf weight -.3709**

Root weight -.2684**

Tuber number -. |5I5
Tuber Bulking Phase

Leaf weight -.4749**

Root weight -.4429**

Average tuber wt. -.5 l 54**

 

E. enetrans

g1; Root Total
-.4637** -.2772** .4044**
-.3327** -. l 285*” -.2223**
-.8 l 43** -. l 678** -.32 l 0**

. I 829** .049 l .0837*

. l003** .0226 .0422
-.0509 -. l442** -. l354*

 

* Significantly different from r=0 at 5% level

** Significantly diffeent from r=0 at I% level

116

Table 28. Simple correlation coefficients between E. decemlineata and E.
metrans.

 

 

E. enetrans

Soil Population Root Population

 

 

Density ' Density Total
E. decemlineata
at tuber initiation -.06460 -.l389l -.l2895
at tuber bulking -.20842 -.40597* -.3959 l *

 

 

* Significmtly different from r=0 at the 5% level

** Significantly different from r=0 at the I% level

 

117

environmental effects are the most important components, explaining 7I% of
the variability in average tuber weight per plant. Changes in root weight during
the tuber growth phase explaining 2% of the total variability. From this it
appears that final tuber yield is determined mainly by the influences which
occur later in the season during the tuber growth phase.

Introducing E. decemlineata and E. penetrans into the path diagram shows
how the effects of each organism is mediated through the leaf and root
systems, respectively. The greatest affect that E. penetrans has on final tuber
yield occurs during the early stage of plant growth when tubers are being
formed as indicated by the relative sizes of the path coefficients between E.
metrans and root weight and between root weight and its respective yield
component. Not only is the path between root weight and tuber number
greatest during the tuber initiation phase, P=0.2883, but the path coefficient
between E. penetrans and root weight is greatest at this time, P=0.2223.

E. decemlineata exerts its primary influence on final tuber yield during
the tuber growth phase. The relative affect that E. decemlineata has on leaf
weight increases 9% as the season progresses, but it is during the tuber growth
phase where the largest path coefficient (P=0.4749) or greatest contribution to
final tuber yield is determined.

SOLANUM TUBEROSUM AGROECOSYSTEM

Soil fumigation, nitrogen fertilizer and length of defoliation period by E.
decemlineata all influenced final yield of §. tuberosum (Table 29). Total yield
increased with nematicide and fertilizer application when no defoliation of _S.

tuberosum by E. decemlineata was permitted. Total yield was significantly

Table 29.

Influence of selected management inputs on the final tuber yield of
§. tuberosum (cv Superior).

 

Treatment

Tuber yield (quintal/ha)

 

Nitrogen2 Fumigation3 5.3 cm

 

Defoliationl (kg /ha) (I /ha) < 5 cm > 8 cm Total
None 0 0 265.7 bc" 8.0 ab 7.4 ab 281.0 b
560 0 288.7 c 6.2 a 37.0 c 33 L9 c
0 93.5 282.9 c l0.0 abc I8.8 b 3| I.7 c
560 93.5 289.4 c 7.6 ab 59.5 c 356.5 c
Early-season 0 0 205.4 a 9.9 abc 3.3 a 2 l 8.5 ab
560 0 2 l 6.5 ab 7.l ab 5.8 ab 229.4 ab
0 93.5 2 l8.l ab l I.4 be 3.3 a - 232.7 ab
560 93.5 207.0 a 7.6 ab 8.I ab 222.7 ab
Full-season 0 0 209.4 a 7.3 ab 5.0 ab 22 I.7 ab
560 0 l97.l a 9.0 abc 2.9 a 209.I a
0 93.5 226.l ab I2.2 c 5.2 ab 243.6 ab
560 93.5 22 I.7 ob 8.3 abc l0.0 ab 239.9 ab

 

lFoliar applications of Methamidiphos IOG; 3.4 kg/ha a.i. as needed for E.

decemlineata control.

2Nitrogen fertilizer (NPK 20-I0-l0) applied at planting, plus l62.5 kg/ha Urea
(45% N) at hilling on June 22, I979.

3Mom 11 broadcast injected to a 20 cm soil depth on May 1, 1979.

“Column means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

119

(P=0.05) increased at the no defoliation "level when compared to the
unfertilized, fumigated full-season defoliation level. Total yields were
significantly (P=0.05) increased at the no defoliation level, with the exception
of the no defoliation level with no fertilizer or nematicide application. Highest
total yield of Grade A (5-8 cm diameter) tubers was observed in the no
defoliation levels (Table 29). Yield of A grade tubers was significantly (P=0.05)
increased with no defoliation with the exception of the no defoliation
unfertilized level with no nematicide. Highest total yield of B grade ( < 5 cm
diameter) occurred in both the early and full-season defoliation levels with
nitrogen applied (Table 29). Yields of oversized tubers ( > 8 cm diameter)
increased with application of fertilizer (Table 29).

The affect of soil fumigation, nitrogen fertilizer and E. decemlineata
defoliation on plant growth was inconclusive. No significant (P=0.05)
differences in root fresh weight or in tuber number were observed season-long
(Tables 30 and 3|, respectively). No significant interaction between
defoliation, fertilization or nematicide was detected. Foliage fresh weight was
significantly (P=0.05) higher in the no defoliation level with nematicides during
the final plant sampling (Table 32). Foliage fresh weight increased with soil
fumigation, nitrogen fertilizer and as the length of the defoliation period
decreased. Tuber fresh weights were generally lower as the length of the
defoliation period increased and increased with fertilizer application (Table 33).

No significant (P=0.05) differences in the soil population densities of E.
penetrans were observed except for the sample of August 6, I979
(DD |0c=56l.8). Soil population densities of E. penetrans were significantly
(P=0.05) lower in the early season defoliation, fumigated levels without

fertilizer compared to the unfertilized early-season defoliation levels with no

120

Table 30. Influence of selected management inputs on root fresh weight of _S_.
tuberosum (cv Superior).

 

 

 

 

Treatment Root fresh weight (Grams)5
Defoliation' Nitrogen2 Fumigation3 317.0 556.8 934.0
(kg/ha) (l/ha)

None 0 0 7.4 a4 10.1 a 10.4 a
560 0 8.I a I3.4 a l 2.4 a

0 93.5 8.3 a I0.9 a l0.8 a

560 93.5 7.3 a 9.7 a l2.8 a

Early-season 0 0 7.9 a I2.4 a 8.5 a
560 0 6.0 a I2.2 a l 2.3 a

0 93.5 5.5 a l2.3 a l0.l a

560 93.5 6.6 a 9.0 a l0.7 a

Full-season 0 0 6.7 a I0.7 a 9.4 a
560 0 7.2 a l0.9 a l0.4 a

0 93.5 7.2 a l0.7 a 9.2 a

560 93.5 6.7 a l3.4 a 8.6 a

 

lFoliar applications of Methamidiphos IOG; 3.4 kg/ha a.i. as needed for E.
decemlineata control.

2Nitrogen fertilizer (NPK 20-l0-l0) applied at planting, plus l62.5 kg/ha Urea
(45% N) at hilling on June 22, I979.

3Telone ll broadcast injected to a 20 cm soil depth on May I, I979.

“Column means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newmm-Keuls Multiple nge Test.

5Degree day accumulation base I0 C.

121

Table 3 l. Influence of selected management inputs on the number of tubers of
_S_. tuberosum (cv Superior).

 

 

 

 

Treatment Tuber number per plant5
Defoliation' Nitrogen2 Fumigation3 317.0 556.8 934.0
(kg/ha) (Ilha)
None 0 0 0.0‘1 1 1.3 a 8.3 a
560 0 0.0 I3.5 a I l.3 a
0 93.5 0.0 I l.8 a 9.2 a
560 93.5 0.0 l2.5 a I3.8 a
Early-season 0 0 0.0 l3.0 a 8.8 a
560 0 0.0 l3.5 a 9.2 a
0 93.5 0.0 l3.6 a l8.7 a
560 93.5 0.0 I2.6 a 9.0 a
Full-season 0 0 0.0 9.5 a 7.8 a
560 0 0.0 l0.4 a 7.7 a
0 93.5 0.0 l2.7 a 8.3 a
560 93.5 0.0 I3.8 a 9.3 a

 

IFoliar applications of Methamidiphos IOG; 3.4 kg/ha a.i. as needed for E.
decemlineata control.

2Nitrogen fertilizer (NPK 20-l0-l0) applied at planting, plus l62.5 kg/ho Urea

(45% N) at hilling on June 22, I979.

3Teione 11 broadcast injected to a 20 cm soil depth on May 1, 1979.

“Column means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

5Degree day accumulation base l0 C.

122

Table 32. Influence of selected management inputs on foliage fresh weight of
§. tuberosum (cv Superior).

 

 

 

 

Treatment Foliage fresh weight (Grams)5
Defoliation' Nitrogen2 Fumigation3 556.8 934.0
(kg/ ha) ( l/ha)
None 0 0 76.9 a4 196.9 a
560 0 76.9 a 4l8.6 b
0 93.5 86.4 a 22l.3 a
560 93.5 56.2 a 408.7 b
Early-season 0 0 75.0 a l6 I.4 a
560 0 56.I a 239.0 a
0 93.5 54.4 a 2 l 7.6 a
560 93.5 58.8 a 2 l0.6 a
Full-season 0 0 57.2 a I76.5 a
560 0 63.4 a 203.6 a
0 93.5 69.2 a l69.6 a
560 93.5 5l.5 a 200.9 a

 

lFoliar applications of Methamidiphos IOG; 3.4 kg/ha a.i. as needed for E.
decemlineata control.

2Nitrogen fertilizer (NPK 20-I0-l0) applied at planting, plus l62.5 kg/ha Urea
(45% N) at hilling on June 22, I979.

3Te1one 11 broadcast injected to a 20 cm soil depth on May 1, 1979.

4Column means followed by the same letter are not significantly different

(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

SDegree day accumulation base l0 C.

123

Table 33. Influence of selected management inputs on tuber fresh weight of §.
tuberosum (cv Superior).

 

 

 

 

Treatment Tuber fresh weight (Grams)5
. . - 2 - - 3
Defo| tatton l “(143/$33" Fumation 556.8 934.0
None 0 0 236.9 abc‘1 668.8 ab
560 0 228.3 abc 958.I b
0 93.5 25l.8 bc 778.3 ab
560 93.5 l53.3 abc 867.7 ab
Early-season 0 0 273.3 c 656.5 ab
560 0 I I3.8 a 648.4 ab
0 93.5 267.4 bc 774.6 ab
560 93.5 I35.9 ab 5 I 8.4 a
Full-season 0 0 204.2 abc 676.8 ab
560 0 l65.2 abc 566.9 ab
0 93.5 27 I.7 c _ 724.9 ab
560 93.5 209.3 abc 589.I ab

 

lFoliar applications of Methamidiphos IOG; 3.4 kg/ha a.i. as needed for E.
decemlineata control.

2Nitrogen fertilizer (NPK 20-I0-l0) applied at planting, plus l62.5 kg/ha Urea
(45% N) at hilling on June 22, I979.

3Telone‘ ll broadcast injected to a 20 cm soil depth on May I, I979.

4Column means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

5Degree day accumulation base l0 C.

124

 

 

 

 

Table 34. Influence of selected management inputs on plant fresh weight of §.
tuberosum (cv Superior).
Treatment Plant fresh weight (Grams)5
Defoliation' Nitrogen2 Fumigation3 317.0 556.8 934.0
(kg/ha) ( I/ ha)
None 0 0 84.2 a4 274.0 ab 895.3 ab
560 0 85.0 a 273.4 ab l42l.7 b
0 93.5 94.7 a 284.8 ab l032.7 ab
560 93.5 63.5 a l83.6 ab l3l7.l ab
Early-season 0 0 83.0 a 3 l0.5 b 844.0 ab
560 0 62.l a l50.0 a 923.2 ab
0 93.5 59.9 a 302.8 b I027.8 ab
560 93.5 65.4 a I66.9 ab 757.4 a
Full-season 0 0 63.9 a 237.2 ab 876.8 ab
560 0 70.6 a I99.5 ab 799.9 a
0 93.5 76.3 a 305.0 b 924.9 ab
560 93.5 58.2 a 252.3 ab 8l6.l a

 

'Foliar applications of Methamidiphos IOG; 3.4 kg/ha a.i. as needed for E.

decemlineata control.

2Nitrogen fertilizer (NPK 20-l0-l0) applied at planting, plus l62.5 kg/ha Urea
(45% N) at hilling on June 22, I979.

3Telone ll broadcast injected to a 20 cm soil depth on May I, I979.

“Column means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newmm-Keuls Multiple Range Test.

SDegree day accumulation base l0 C.

Table 35.

Influence of selected management inputs on soil population densities

125

of Pratylenchus penetrans on _S_. tuberosum (cv Superior).

 

Treatment

 

E. metrans / I00 cm3 soils

 

 

Defo- NiTl’ogefleumigation3
Iiationl (kg/ha) (I/ha) 47.1 137.6 319.8 561.8 920.1 1204.1
None 0 0 42.8a4 28.0ab 20.4a 80.6b l78.4a 97.6b
560 0 45.0a 29.4ab I7.0a 24.0ab 157.0a 78.4b
0 93.5 59.80 21.6ab l5.4a 26.8ab 115.2a 36.8a
560 93.5 40.2a l8.0ab 19.6a 18.8ab 73.4a 24.4a
Early- o o 34.2a 22.0ab 25.8a 80.8b 149.8a 61.2a
season 560 o 46.0a 29.4ab 28.8a 9.2a 97.2a 62.2a
o 93.5 43.0a 22.2ab 20.8a 41.0ab 128.6a 5|.0a
560 93.5 28.4a 6.6a Il.0a 15.2a 65.8a 36.8a
Full- 0 0 3l.4a 26.8a 28.6a 35.4a 160.8a 75.4b
season 560 0 24.0a 43.4b I7.6o 2|.4ab 94.6a 52.4a
0 93.5 35.2a 11.0ab 18.2a 24.8ab 240.0a 26.4a
560 93.5 31.4a 10.0ab 14.6a 18.2ab 78.0a 35.4a

 

lFoliar applications of Methamidiphos IOG; 3.4 kg/ha a.i. as needed for E.

decemlineata control.

2

(45% N) at hilling on June 22, I979.

3

Telone ll broadcast injected to a 20 cm soil depth on May I, I979.

Nitrogen fertilizer (NPK 20-l0-I0) applied at planting, plus l62.5 kg/ha Urea

“Column means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

SDegree day accumulation base l0 C.

 

126

 

 

 

 

 

Table 36. influence of selected management inputs on root population density
of Pratylenchus penetrans on §. tuberosum (cv Superior).
Treatment E. @etrans per gram root tissueS
Defoliation I Nitrogen2 Fumigation3
(kg pm) ( | lha) 5 l4.2 668.3 954. l
None 0 0 l04.6c1‘I l47.0a 41 1.0a
560 0 82.8 a I50.8 a 386.0 a
0 93.5 96.4 a l89.2 a 563.6 a
560 93.5 50.2 a I l8.4 a 288.0 a
Early-season 0 0 96.0 a 289.6 a 573.2 a
560 0 85.4 a l43.4 a 490.6 a
0 93.5 98.4 a 240.6 a 325.8 a
560 93.5 54.0 a I02.2 a 207.4 a
Full-season 0 0 89.6 a |56.6 a 407.2 a
560 0 73.2 0 l7 I.6 a 300.6 a
0 93.5 85.0 a l95.2 a 447.8 a
560 93.5 49.6 a 64.8 a 284.8 a

 

IFoliar applications of Methamidiphos IOG; 3.4 kg/ha a.i. as needed for E.

decemlineata control.

2

Nitrogen fertilizer (NPK 20—l0—l0) applied at planting, plus l62.5 kg/ha Urea
(45% N) at hilling on June 22, I979.

3Telone ll broadcast injected to a 20 cm soil depth on May I, I979.

“Column means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newmm-Keuls Multiple Range Test.

5Degree day accumulation base l0 C.

127

nematicide (Table 35). There were no significant (P=0.05) differences in root

population densities of E. penetrans season-long (Table 36).

DISCUSSION

Few studies have been conducted to examine the joint interaction of plant
pests. Only recently has-emphasis been placed on the importance of identifying
crop losses associated with the joint action of organisms affecting plant growth,
development and yield. Knowledge of these associations will enhance our basic
understanding of the dynamics of complex agro-ecosystems and aid in the
development of new pest management strategies.

Potato plants are influenced by sets of dynamic biotic md abiotic factors.
Many of these factors remained uncontrolled when these studies were
conducted in the field. These studies were conducted to determine the affects
of E. decemlineata and E. penetrans on the growth of the potato plant in its
natural environment. The uncontrolled environmental effects represent a major
influence affecting plant growth in these studies. A significant portion of the
variability in the number of tubers formed and the average tuber weight is not
explained by the effects of E. decemlineata and E. penetrans. The sources of
this variability can be attributed to such factors as genetic variability,
uncontrolled environmental and pathological factors and experimental error.
complementary studies need to be conducted both in field and laboratory
settings where the abiotic and biotic factors can be more rigidly controlled.
Adequate replication, involving more factors, may need to be examined to
explain the differences in growth, development and yield of _S_. tuberosum.

E. pe_netrans and E. decemlineata are major pests of the Michigan potato

cropping system. The symptoms commonly associated with E. penetrans are a

 

128

 

  
    

 

 

 

LET-IF DRY llT. VS. TIliE 9ND LFIRVFIL DENSITY
05-
N .
0 -NONE
A -I0/PLFINT

1:; a- O ~20/PLHNT
Q
[U .
(D to...
m c-
Q
j—
3 .
>- 3‘
a:
D
1.1.
C
1.1.1 ._
-l ID

5'l 1 1 1 - 1

0 300 800 900 1200 1500

RCCUI‘I. DEGREE DRY (898E 10 C)

 

 

 

Figure 21. Influence of three plant densities of _L_. decemlineata on
leaf dry weight of §_. tuberosum (cv Superior).

129

 

 

 

 

 

8R00T DRY HT VS. TIME FIND LRRVHL DENSITY
..'.‘l
c:
“3- NDNE
__ a
m ‘8
1:
CE
Z I:
C) G}_
"' o
._’
3 ID / PLFINT
>- S
:5 =1" 9
'5 \
O o t
I: o: 20 / PLHNT
o-
i:
9
o-I I l l l
0 ' 300 600 900 1200
I-lCCUl‘l. DEGREE DRY IBRSE 10 Cl

 

 

 

Figure 22. Influence of three plant densities of L. decemlineata

. on root dry weight of _S_. tuberosum (cv Superior).

 

130

 

PLRNT DRY NT VS. TIHE 0ND LRRVRL DENSITY

150.
I

PLRNT DRY HT IGRHHSI

 

 

 

0 300 500 900 1200 1500
RCCUH- DEGREE DRY (3955 10 CI

 

 

 

Figure 23. Influence of three plant densities of E. decemlineata
on plant dry weight of §, tuberosum (cv Superior).

 

 

131

 

 

 

 

é TUBER DRY HT VS. TIIIE FIND LRRVFIL DENSITY
O-
NDNE
c5-
__ a
in
t
C
K
o O.-
" to 10 / PLHNT
[—
3
)-
m .
c1 3-
M
g .
3 20 / PLRNT
l— .
o-
N
61 l 1 l _l
0 300 800 900 1200 1500
RCCUI‘I. DEGREE DRY (DRSE 10 C)

 

 

 

Figure 24. Influence of three plant densities of _L_. decemlineata
0n tuber dry weight of _S_. tuberosum (cv Superior).

132

gradual decline or lack of plant vigor. This is in stark contrast to the rapid,

striking changes that occur as a result of defoliation of potato plants‘by E.

decemlineata. Despite the dramatic overt differences, both pests can

 

significantly influence growth, development and yield by the effects mediated
through the root and leaf systems, respectively.

E. decemlineata and the affect it has on the leaf system is the most

 

importmt biotic component influencing final tuber yield. The direct effect of
E. decemlineata feeding is a reduction in leaf weight and leaf surface area.
Defoliation increases with time as the larvae advance through successive
instars and densities increase (Fig. 2|). As beetles reduce leaf dry weight,
there is a corresponding reduction in the plant root dry weight (Fig. 22). This is
evidently a beetle-mediated plant response to severe levels of defoliation.
These changes in the leaf and root systems are directly reflected in the reduced
plant and tuber weights through time for the beetle-infested treatments (Figs.
23 and 24, respectively). E. decemlineata exerts its primary influence on final
tuber yield during the tuber growth phase (Fig. 25). This is indicated in the path
diagram by an increase with time in the affect of E. decemlineata on leaf
weight as well as an increase in the affect of leaf weight on its respective yield
component. Grafius (unpublished data) showed that defoliation occurring later
in the season was far more important in determining final tuber yield than
defoliation occurring earlier in the season. These results provide further
evidence of the importance of late-season defoliation by E. decemlineata on
final tuber yield. Future insect control recommendations based on crop
phenology and field population densities of E. decemlineata are needed.

The response of plant growth to various soil population densities of E.

penetrans in these studies was negligible. Few significant differences

133

 

YIELD VS NENRTDDE BNO BEETLE DENSITY

5000

4000

 

3000

2000

 

YIELD (GRHH / 1.83 H RON)
1000

 

 

0 10 20'
BEETLE DENSITY (PLBNT)

 

 

 

Figure 25. Influence of three population levels of P. enetrans and
L. decemlineata on final tuber yield of E. tu rosum
ch SuperiorT.

 

 

134

attributable to E. penetrans were evident in any of the measured plant growth
parameters. Changes in root weight, which are typically used as indicators of
plant response to nematode infection, were small and statistically not
significant. Examining this relationship through path coefficient analysis
showed that the impact of E. @etrans on root weight and influence of root
weight on final tuber yield decreased as the season progressed. The major
impact of E. penetrans on final tuber yield was associated with a reduction in
the number of tubers formed during the early stages of plant development. A
more accurate assessment of the influence of E. fletrans on plant growth may
have been possible if variables which compared the inhibition or interference of
root function had been used. Collecting and quantifying information of this
kind is expensive, time-consuming and may have some technological
constraints.

E. wetrans may have been biologically more important in its affect on
the nutrient relationships of the potato plant. This is exhibited in the response
of §. tuberosum to fertilizer and soil fumigants. Even though the results are
inconclusive, they do indicate an increased level of plant growth and yield
response to nitrogen fertilizers when nematodes are reduced to low population
levels in the field. Research needs to be continued into the affect of E.
penetrans on the water and nutrient relationships associated with potato plant
growth.

Both E. wetrans and E. decemlineata affect final tuber yield, with E.
decemlineata having the most significant impact in terms of decreasing yields
(Fig. 25). Total yield of potatoes decreased 66% with increasing beetle
densities per plant and 27% with increasing population density of E. penetrans.

The joint impact of E. penetrans and E. decemlineata was additive in their

 

 

135

 

260
1

0 - 0 BEETLES/PLRNT
A -10 BEETLES/PLRNT
t -20 BEETLES/PLRNT

200
1

150
1

P. PENETRRNS (PER GRHH RDDTI

 

 

 

0 300 800 ' 900 1200 1500
DEGREE DRY (BBSE 10 C I

 

 

 

Figure 26. Influence of three plant densities of E. decemlineata
on the root population density of _P_. penetrans.

 

136

effects on final tuber yield. Knowledge of the effects of various pests and the
critical stage of plant susceptibility to these pests will aid in the development
of economic thresholds that take into account the joint action concept.

It was hypothesized that the response of §. tuberosum to various
combinations of stress would, in turn, influence the growth and reproductive
rate of E. decemlineata and E. genetrans. No plant-mediated effects were
observed that influenced larval populations of E. decemlineata. The nematode
populations wee not at levels which significantly affected the quantity or
apparent quality of leaf material available to E. decemlineata. This may
possibly occur when nematode populations are at levels which would stunt the
growth of the plant and limit the food resources available to E. decemlineata.

Larval feeding by E. decemlineata appears to directly influence the

 

population dynamics of E. penetrans. By reducing the leaf weight through time,
beetle feeding influences the size of the total root system available for
nematode colonization. Smaller, less extensive root systems would limit the
number of soil nematodes directly exposed to roots in close proximity, thereby
reducing the probability of infection and survival. Even the nematodes which
do find and penetrate potato roots are influenced by E. decemlineata
defoliation. As E. decemlineata feeding continued into the season, a shift in
plant maturity occurred. Early defoliation appeared to delay plant maturity.
As defoliation increased, the plant was incapable of providing the necessary
photosynthates to sustain normal growth. This resulted in an early senescence
in roots and a decrease in the number of E. wetrans per gram of root (Fig. 26).
A number of possible mechanisms to explain this are possible (e.g., limited
reinfection from soil and root nematodes, a decrease in the survival or

reproductive potential of females within the roots). A change in the nutritional

 

137

 

O

3" o - 0 BEETLES/PLHNT
A -10 BEETLES/PLRNT
e -20 BEETLES/PLRNT

”—1

p

 

P. PENETRBNS (100 CH SOIL)

 

 

0 300 DOD 900 1200 1500
DEGREE DRY (8935 10 c 1

 

 

 

Figure 27. Influence of three plant densities of E. decemlineata on
the soil populationdensity of E. penetran‘s.

 

138

quality of the roots perhaps occurred which resulted in the decrease in the
number of E. penetrans per gram of root in the beetle-infested treatments.
This would explain why E. wetrans were not recovered in the root extraction
procedures. No differences were observed in soil population densities of E.
metrms at the defoliation levels (Fig. 27).

Path coefficient analysis (PCA) was used in this study as a conceptual
framework for data collection as well as a method for analyzing the results. It
was used in addition to other malytical techniques. PCA was not used as a
procedure for demonstrating cause and effect. It was used as a descriptive and
intepretive tool to evaluate the interrelationships between variables. The
technique was based on the construction of a qualitative diagram in which the
path coefficients were calculated according to a specified format provided in
the path diagram (F ig.-20). The diagram assumes that unit chmges in leaf or
root weight caused by E. decemlineata and E. penetrans, respectively, will
produce chmges in the various yield components of §. tuberosum. It should be
noted that my ambiguities in the underlying assumptions of the path diagram
will lead to ambiguities in the results obtained through path coefficient
analysis. The proposed structure of the path diagram and its underlying
biological and physiological assumptions must therefore be closely scrutinized
and evaluated.

The path diagram is based on the sequential development of §. tuberosum
and the influence E. penetrans, E. decemlineata and the environment have on
the plant during their respective developmental stages. Each step in the
sequence is influenced by a set of environmental factors, as well as what has
occurred during earlier stages. The plant has distinct, time-ordered

developmental stages in which the relationships between leaves, roots and

 

139

tubers is dynamic. The results obtained represent an assessment of the impact
of stress at different times during §. tuberosum phenology. This analysis

assumes that the effects of various biotic and abiotic influences cm be
measured at distinct points in time and space. The effects measured at these
times must be representative of the impacts that the plant stress factors have
on plant growth.

The interpretation of the path diagram is applicable only to the current
state of the plant at the time plant samples were taken. Evaluating the effects
of stress at my other time will not change the structure of the path diagram
but could have a significant impact on the magnitude of the path coefficients.
This cm be vividly illustrated during the tuber initiatim process. The
phenology of the potato plant follows a distinct developmental sequence in
which tubers are initiated at various times during the growth of the plmt. They
are continually being formed and reabsorbed during plant development.
Temporary delays in plantmaturity due to pest population pressures may result
in significant differences in the number of tubers observed between treatments
at my one point in time. These differences in plant respmse ma not be evident
during later plant sampling dates. Genetic variability in the population of
plants being sampled may also obscure these biological and physiological
relationships, especially if the number of samples or replications with the
experimental design is small. Sampling errors associated with such dynamic
processes as tuber formation and the obtaining of representative plant samples
during these developmental processes can be great, and can lead to
misinterpretation of the data. When studying correlations, it is ’of utmost
importmce to recognize the nature of the populatim under consideratim,

inasmuch as the magnitude of the correlation coefficients and the

 

140

corresponding path coefficients from which they are derived cm be influenced
by the choice of individuals upon which the observations are made.

Regardless of the apparent limitations involved in the interpretatim of
the results, path coefficient analysis does provide some useful insights into the
dynamics of _S_. tuberosum growth, development and yield. The technique, when
used in the initial conceptualization of an experiment, allows the investigator
to hypothesize on how the interacting biological forces drive the system. Other
statistical techniques such as regression or simple correlation analysis do not _-
provide these powers of ‘ interpretatim. They are concerned with qumtitatively
estimating the relationships between dependent and independent variables. It
has no point of view other than describing a linear relationship among variables.
Other malytical techniques have the same shortcomings.

Path coefficient malysis is flexible in that my number of variables cm be
examined in a more holistic and systematic mmner. In this analysis, the
simplest design with the fewest number of variables which will adequately
describe the system within a predetermined level of precision can be
determined. Not only can plant growth response to outside perturbations be
speculated upon, but levels of importmce can be assigned to the variables
describing the interrelationships of the system.

Path coefficient analysis' most useful role in research is not in the final
stages of a research program, but rather it is during the early stages when a
sensitivity analysis is needed to identify the most important components
influencing the trajectory of the system. Research priorities and allocation of

resources cm thus be optimized.

141

SUMMARY

Field experiments were used to evaluate the roles of nitrogen, phosphorus

and edaphic pesticides on the growth, development and yield of §. tuberosum

and the population dynamics of E. penetrans. Further studies examining the

joint role of E. penetrans and E. decemlineata on the growth, development and

yield of §. tuberosum and the biology of the concomitant species were

cmducted. To recapitulate some of the important findings:

Tuber yields decreased with increasing plant densities of E.
decemlineata and E. penetrans.

Tuber yields increased with increasing fertilizer rate of N and P.

Both N and P influence the phenological development of _S_. tuberosum
and the attainment of final tuber yield.

Neither N nor P had my detectable influence on E. metrans
population dynamics.

There was no significmt interaction between fertilizer md edaphic
pesticide on the growth, development and yield of §_. tuberosum or
the population dynamics of E. penetrans.

Control of E. penetrans and E. decemlineata can greatly increase
tuber yield.

Based on E. genetrans recovered from soil and root tissue, aldicarb
provided the best season-long control.

It appears that E. penetrans most important influence on tuber yield
is through its affect on tuber set. Control of E. penetrans increased
tuber set and then N or P limited yield. With an increase in N or P

rate, the small tubers increased in size.

 

142

E. metrans affects final tuber yield in its alteration of the nutrient

requirements of _S_. tuberosum for optimizing yield.

The fungicidal properties of edaphic pesticides needs to be examined
more closely in relation to tuber yields to explain why yields increase
in some cases even though control of E. wetrans could not be
detected.

Significant error factors may be involved with measuring plant
biomass in units of plant fresh weight.

Path coefficient malysis was used as an interpretive tool to identify
the importmce of E. decemlineata and E. metrans and the
environmental influences on the yield of §. tuberosum. E. penetrans
most important affect on §. tuberosum occurred during the tuber
initiatim phase, reducing tuber set. E. decemlineata's most
important effect occurred during the tuber bulking phase, reducing
tuber size.

E. decemlineata significantly increased the number of tubers in the
smaller tuber size categories and decreased the number in the larger
tuber size categories.

E. decemlineata significantly reduced the total weight of tubers in
the larger tuber size categories.

E. decemlinth by reducing leaf weight or surface area, reduced
population densities of E. metrons by influencing the size and

possible nutritional quality of the root system.

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Potter, J.W. and T.H.A. Olthof. I974. Yield losses in summer-maturing
vegetables relative to population densities of Pratylenchus @etrans and

Meloidggme h_apla. Phytopathology 64:l072-l075.

Proctor, J.R. and C.F. Marks. I974. The determination of normalizing
transformations for nematode count data from soil samples and of
efficient sampling schemes. Nematologica 20:395-406.

Seinhorst, J.W. I950. De betekenis van de toestand van de grand voor optreden
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(Nematoda: Tylenchidae). Univ. Calif. Publ. loch-573447370.—

Steiner, G. I927. Tylenchus ratensis and various other nemas attacking
plants. J. Agric. Res. 35:96l-98I.

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No. l, J. Nematol., 4 pp.

Tai, C.C.C. I975. Analysis of genotype-environmental interactions based on
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Taylor, C.E. I953. The vegetative development of the potato plant. Ann.
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Taylor, P.L., J.M. Ferris and V.R. Ferris. I97 I. Quantitative evaluation of the
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Thistlewayte, B. I970. Reproduction of Pratylenchus penetrans (Nematoda:
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152

Ting, H.H. and G. Fraenkel. I968. Selection md specificity of the Colorado
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Townshend, J.L. I972. Influence of edaphic factors on penetration of corn
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Townshend, J.L. I978. Infectivity of Pratylenchus penetrans on alfalfa. J.
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153

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APPENDIX A

 

 

 

APPENDIX A
N data - I978

MATERIALS AND METHODS

ROLE OF SOIL NUTRIENTS AND NEMATICIDES
ON §_. TUBEROSUM AND _P_. PENETRANS

A field experiment was conducted in I978 to evaluate the role of soil
nutrients and nematicides on the growth of S. tuberosum and the population
dynamics of _P_. penetrans. Two potato cultivars (Superior and Russet Burbank)
were grown on a McBride sandyloam soil (alfic fragiothods) at the Montcalm
Potato Research Farm in Entrican, Michigan. The farm is separated into two
large north-south rectangular blocks (Fig. 3). During any year, one block is
utilized for current experimental research while the other block is spring planted
to rye or alfalfa. The following spring it is disked and planted. Blocks are
rotated every other year to enhance soil organic content and to reduce

populations of soil-borne organisms and insects detrimental to _S_. tuberosum.

Planting Procedure

Seed pieces (whole certified seed > 5 cm diameter) were planted on May 22
and 23, I978. Each plot consisted of four rows 0.86 m wide and l5.24 m long
with seed spacing of 20 cm. All plots were irrigated with a solid set sprinkler

system according to need determined by measurements of evapotranspiration.

154

 

155

Sampling Procedure

Plant growth and development was measured at various intervals during
I978 and I979. The experimental area was first divided into 5 blocks of equal
size to compare sampling variation within and between treatments.

In I978 an additional study was conducted to examine the joint role of
nitrogen fertilizer md nematicides. In sampling foliage, two plants were
rmdomly selected from the outside rows of each plot. The soil immediately
below each plant was carefully removed to a depth of 93 0.35 m. In I978, the
soil directly below each plant sample was hand-sifted for roots and tubers.

Soil and root populations of E. penetrans were estimated from samples
taken at these times. Soil samples for nematode analysis were taken by core
sampling (IS-20 cores) the two outside rows of each plot and later, after plant
germination, by removing the soil adjacent to the roots of the plant. Root
samples were derived from plants returned to the laboratory for plant growth
analysis. Soil and root populations of E. penetrans were determined using the
centrifugation-flotation technique (Jenkins, I964) and shaker technique (Bird,
I97l), respectively. Estimates of soil and root nematode population densities
were based on ID cm3 of soil and 0.| gram of root.

At various intervals during the I978 season, both 0 I0 and a l00 cm3 soil
md OJ and LO gram root tissue sample were processed to compare the
efficiency and reliability of the estimates achieved by both methods. This was
achieved first by agitating the ID ml vial of nematode suspension and extracting
I.0 ml with a LG ml syringe. Nematodes were counted in a circular petri dish
under a I5X dissecting microscope. Immediately afterwards, the remaining 9.0

ml of nematode suspension was counted and recorded.

 

 

 

156

Harvesting Procedure

Tuber yields were calculated from the harvest of the two center rows of
each plot with a self-propelled potato harvester specifically developed for field
research (Chase 91 a_l., I978). Tubers from each plot were graded and weighed.

A completely rmdom block-two factorial design was used, with each
treatment replicated five times. The data was subjected to m malysis of
variance to statistically examine differences in'plant growth, development, yield

and nematode control.

Nitrogen

A field experiment was conducted in I978 to examine nitrogen levels md
their interactions with selected insect and nematode control programs and to
monitor growth, development and yield of _S. tuberosum (cv Superior). In this
experiment (Table 2), five pesticide treatments (control, aldicarb (Temik ISG),
l,3-D+MIC (Vorlex), carbofuran (Furadan IOG), and thiofanox (Dacamox I 0(3))
were evaluated on cv Superior growth at two nitrogen rates (84 and I68 kg/ha).
All plots received 84 kg/ha of N, P205 and K20 (IS-IS-IS) as a starter fertilizer
banded S cm to the side and below the seed piece. The plots to receive cm added
nitrogen treatment were side-dressed with urea (45% N) at an application rate of
I l2 kg/ha on June l3, I978, and 84 kg/ha on June 22, I978.

In the second nitrogen experiment in I978, nitrogen application rate and
nematicide treatment contributed significantly (P=0.05) to the total yield (Table
l0). Both aldicarb and I,3-D + MIC, of each nitrogen rate, significantly (P=0.05)
increased total yield above the controls. With each nematicide used in this test,
higher total yields generally occurred at the greater nitrogen rate. The I68

kg/ha nitrogen rate increased the average yield by 4%, but this was not

 

 

 

157

significant. Yield of A size tubers was similar to total yield results. The I,3-D +
MIC at both nitrogen rates was significantly (P=0.05) greater than the controls.
Only thiofanox at the higher nitrogen rate significantly (P=0.05) increased large
size tuber yield. There were no significant (P=0.05) differences in B size tuber
yield, although thiofanox at both nitrogen rates resulted in the lowest yield.

Nitrogen fertilization had no significant (P=0.05) affect on nematode
population dynamics. Aldicarb significantly (P=0.05) reduced soil population
densities of _E. penetrans (Table II). This continued season-long until harvest.
Significant (P=0.05) differences in root population density of E. metrans
between plots were apparent season-long (Table I2). Aldicarb at the 84 kg/ha
nitrogen rate generally reduced root population densities season-long over all
plots. Results of root samples taken from July I2, I978, to harvest showed that
aldicarb at both nitrogen rates resulted in the best nematode control.
Carbofuran appeared to decrease root and soil population densities of _P_.
metrans but was significantly (P=0.05) different only from a control on August
I, I978.

Few significant (P=0.05) differences in root weight occurred throughout the
season (Table l3). Carbofuran at the higher nitrogen rate significantly (P=0.05)
increased root weight during the sample of June 25, I978. This may have, by
increasing root weight early, contributed to the higher soil 'and root population
densities of E. penetrans observed in these plots. It appears that thiofanox at
both nitrogen rates delays the growth and development of the foliage and tubers
(Tables I4 and I5, respectively). This resulted in lower foliage and tuber weights
during early season and significantly (P=0.05) higher plant and tuber weights
during the final sample. This may be due in part to the nematicidal and/or plant

growth characteristics of this material.

 

 

 

158

Table Al. Influence of selected management inputs on population density of E.
pgetrans on potatoes (cv Superior).

 

 

 

 

Treatment E. penetrans per l0 cm3 soil“
[mgr/fig]? Pesticide l39.2 24l.2 373.5 543.8 768.0 983.3
84 Check I.2 al 3.8 a 4.0 a 2.8 a 5.4 b 8.4 b
84 Aldicarbz 0.4 a 0.2 a 0.0 a 0.0 a 0.0 a 0.2 a
84 I,3-d 8. MIC3 0.8 a 0.4 a w a 2.0 b I.2 b 3.6 b
84 Carbofuranz 0.6 a 0.4 a 4.0 a 0.6 a 4.2 b 7.6 b
84 Thiofanon 0.8 a m a 5.0 a 0.8 a I.4 b 5.0 b
I68 Check I.8 a I.4 a 5.0 a 3.0 b 5.6 b 9.2 b
I68 Aldicarb LO 0 0.0 a 0.0 a 0.0 a 0.4 a 0.2 a
I68 I,3-D & MIC 2.6 a 0.2 a 4.0 a 2.5 a 3.4 a 3.8 a
I68 Carbofuran LO 0 0.8 a 2.0 a 2.6 a 3.8 a 5.4 0
I68 Thiofanox LO 0 I.2 a LG a I.4 a I.6 a 5.4 a

 

lColumn means followed by the same letter are not significantly different

(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.
2Applied of planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha
on May I, I979.

“Degree day accumulation base l0 C.

159

Table A2. Influence of selected management inputs on population density of E.
Eetrans on potato (cv Superior).

 

 

 

 

Treatment , E. penetrans per 0.I 9 root tissue“
Nitrogen Pesticide 24I.2 373.5 543.8 758.0 983.3
(kg/ha)
84 Check 44.4 b' 3.8 b Io.2 be 35.8 c 5.0 ab
84 Aldicarbz 2.0 a 0.0 a 0.2 a 0.0 a 0.2 a
84 I,3-D & MIC3 20.2 ab 5.5 c 8.4 bc Io.2 b 3.2 ab
84 Carbofuranz I3.o ab 2.4 be 5.2 be 23.2 bc I8.o ab
84 Thiofanon 20.2 ab I.4 be 7.4 be 5.2 b 5.8 ab
I58 Check I5.0 ab 4.0 c I8.o c 38.5 c I4.8 b
I68 Aldicarb 3.2 ab I.8 ab 0.4 a 0.8 a 0.2 a

I68 I,3-D & MIC l4.4 ab 2.6 bc 6.4 bc I8.8 b 7.8 ab
I68 Carbofuran 22.6 ab 6.2 c I I.6 bc I2.2 b 5.8 ab
I68 Thiofanox 8.8 ab I.4 be 3.4 b 6.8 b I3.8 b

 

IColumn means followed by the same letter are not significantly different

(P=0.05) according to the Student-Newmm-Keuls Multiple Range Test.
2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha
on May I, I978.

“Degree day accumulation base I0 C.

160

Table A3. Influence of selected management inputs on the root weight of
potatoes (cv Superior).

 

Treatment Root Weight (grams)4

 

 

Nitrogen 24 I .2 373.5 543.8 768.0 983.3

(kg /ha) Pesticide

 

84 Check 3.I a' 8.9 ab l0.l a ll.Za 5.30
84 Aldicarbz 3.9 a 9.7 ab I I.8 a l0.5 a 5.2 a
84 I,3-D 8. MIC3 3.5 a 9.0 ab I I.3 a 8.3 a 4.7 a
84 Carbofuranz 4.5 a 9.5 ab l0.3 a I0.5 a 5.3 a
84 Thiofanoxz 3.8 a 8.7 ab I0.4 a I0.3 a 4.5 a
|68 Check 3.8 a 8.8 ab 9.5 a l0.0 a 5.3 0
I68 Aldicarb 3.5 a 9.7 ab I0.9 a 9.3 a 4.4 0
I58 I,3-D & MIC 4.I a l0.2 ab l2.3 a 9.2 a 4.9 0
I68 Carbofuran 4.0 a I I.2 b l3.7 a I0.6 a 5.0 a
I 68 Thiofanox 3.0 a 6.6 a 9.9 a 9.9 a 6.8 a

 

lColumn means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha
on May I, I978.

“Degree day accumulation base I0 C.

161

Table A4. Influence of selected mmogement inputs on the foliage weight of

potatoes (cv Superior).

 

 

 

 

Treatment Foliage Weight (grams)h
mgr/51%? Pesticide 24I.2 373.5 543.8 758.0 983.3
84 Check 27.2 a' 290.3 ab 509.7 a 475.3 a 55.7 a
84 Aldicarbz 29.5 a 334. I ab 744.0 a 552.3 a 88.4 a
84 I,3-D 8. MIC3 28.8 a 388.5 b 559.5 a 495.0 a 72.2 a
84 Carbofuranz 3 I.8 a 299.2 ab 5I2.9 a 50I.7 a 50.5 a
84 Thiofanoxz 27.5 a 249.2 a 593.3 a 582.9 a I33.0 a
I58 Check 30.2 a 285.3 ab 592.4 a 509.4 a 90.4 a
l68 Aldicarb 34.8 a 405.2 b 742.9 a 535.2 a I35.0 a
I58 I,3-D & MIC 30.5 a 383.0 b 788.7 a 587.5 a I I I.2 a
I68 Carbofuran 3 I.7 a 357.3 ab 67 I.4 a 59I.2 a . I I6.8 a
I58 Thiofanox 24.2 a 230.8 a 502.7 a 507.9 a 2I I.4 b

 

IColumn means followed by the same letter are not significantly different

 

(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.
2Applied of planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 I/ha
on May I, I978.

“Degree day accumulation base I0 C.

Table A5. Influence of selected mmagement inputs on the tuber weight of

162

potatoes (cv Superior).

 

 

 

 

 

 

Treatment Tuber Weight / Plant (grams)4
Nitrogen Pesticide
(kg/ha) 373.5 543.8 758.0 983.3
84 Check 9.0 e' 3 l0.7 a 757.7 a 87 I.0 a
84 Aldicarbz I4.9 ab 354.7 a 832.3 a 923.4 a
84 I,3-D 8 MIC3 29.I b 370.5 a 8I0.5 a I07 I.2 a "i
84 Carbofuranz I7.3 ab 329.7 a 733.5 a 905.0 a
84 Thiofanoxz 8.9 a 28 I .8 a 725.4 a 822.8 a
I58 Check I5.5 ab 255.4 a 8I7.2 a 87 I.8 a _
I58 Aldicarb 24.8 ab 385.7 a 775.0 a I I2 I.8 0
I58 I,3-D 8 MIC 20.I ab 4I9.4 a 843.4 a I088.8 0
I68 Carbofuran 20.6 ab 355.I a 847.6 a 8| 9.4 0
I58 Thiofanox 7.3 a 255.0 a 78 I.0 a I I l3.0 a

 

Column means followed by the same letter are not significantly different

(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha
on May I, I978.

“Degree day accumulation base I0 C.

163

Table A6. Influence of three levels of nitrogen and four pesticides on the yield
and size distribution of Superior potatoes (I978).

 

 

 

 

 

Treatment Yield (quintal/ha)
$333?" Pesficide Total 1512!? $5.23. $53.?
84 Check 337 a I4.I a 309 a I3.4 a
84 Aldicarb 392 be I3.4 a 370 bcd l3.2 a
84 I,3-D8 MIC3 4I6c 8.I a 393 cd l4.3 a
84 Carbofuran 362 ab 9.4 a 337 ab l4.3 a
84 Thiofanon 379 abc I78 0 35I abc l0.6 a
I68 Check 352 ab l0.8 a 330 ab I I.0 a
I68 Aldicarb 442 c l7.0 a 39l cd I3.9 a
I58 I,3-D 8 MIC3 425 c l2.2 a 400 d I3.4 a
I68 Carbofuran 375 abc I0.4 a 353 abc l L9 0
I68 Thiofanox 392 bc 28.8 b 252 abc I0.I a

Treatment Means
84 - 377w l2.5w 352w l3.I w
I68 — 393 w I5.8 w 365 w l2.l w
Check 344 x l2.4 x 320 x I2.2 y
Aldicarbz 407 z l5.2 x 380 z l3.6 y
Carbofuran 368 xy 9.9 x 345 xy l3.I y
Thiofanox 384 y 23.3 y 352 y l0.4 x

 

lColumn means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman-Keuls Multiple nge Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha

on May I, I978.

4Degree day accumulation base l0 C.

APPENDIX B

164

Table BI. Influence of selected management inputs on the root weight of

potatoes (cv Superior).

 

Treatment

 

Root Weight (grams)4

 

 

mgr/5‘2? Pesticide 24I.2 373.5 543.8 758.0 983.3
84 Check 4.9 a' 7.8 a 9.8 0 I00 a 4.4 a
84 Aldicarbz 4.3 a 7.8 a I0.I a 8.0 a 4.8 a
84 I,3-D 8 MIC3 4.5 a 8.5 a 9.I a 7.0 a 5.4 a
I68 Check 4.9 a 7.4 a 8.9 a 8.0 a 5.7 0
I58 Aldicarb 4.I a 8.5 a 8.I a 7.4 a 5.5 a
I68 I,3-D 8 MIC 3.9 a , 9.4 a 8.0 a 8.4 a 4.5 a «
335 Check 5.I a 8.5 a I0.4 a 8. I a 7.2 a
335 Aldicarb 3.5 a l0.6 a I0.5 a 7.4 a 5.3 a
335 I,3-D 8 MIC 5.0 a I0.5 a 7.9 a 8.0 a 5.7 a

 

Column means followed by the same letter are not significantly different

(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha

on May I, I978.

4Degree day accumulation base I0 C.

 

165

Table BZ. Influence of selected management inputs on tuber weight of potatoes
(cv Superior).

 

 

 

 

Treatment Tuber Weight / Plant (gramsf‘

Nitrogen Pesticide

(kg/ha) 373.5 543.8 758.0 983.3
84 Check I2.5 a' 237.5 a 758.4 a 984.3 a
84 Aldicarbz I7.7 a 307.4 a 773.5 a 880.3 a
84 I,3-D 8 MIC3 I7.0 a 358.7 a 753.0 a I mm 0
I58 Check 8.0 a 285.I a 595.0 a I I03.4 0
I58 Aldicarb I4.4 a 235.I a 837.5 a I07I.5 a
l68 I,3-D 8 MIC 22.3 a 33 L9 a 573.4 a 953.3 a
335 Check I I.0 a 2 I 5.8 a 592.8 a 858.4 a
335 Aldicarb I4.2 a 284.4 a 808.5 a 980.0 a
335 I,3-D 8 MIC 25.4 a 354.9 a 752.2 a I I32.0 a

 

'Column means followed by the same letter are not significantly different

(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied of planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3

on May I, I978.

4Degree day accumulation base l0 C.

Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha

 

166

 

 

 

 

Table B3. Influence of selected management inputs on foliage weight of
potatoes (cv Superior).
Treatment Foliage Weight (grams)4

lag/5%)" Pesticide 24I.2 373.5 543.8 758.0 983.3
84 Check 37.l 8' 254.5 a 430.3 a 5| I.5 ab 57.I a
84 Aldicarbz ’ 32.I a ' 293.4 a 524.8 a 557.9 ab I70.0 a
84 I,3-D 8 MIC3 30.I a 397.9 ab 547.4 a 500.9 ab I49.0 a
I68 Check 33.9 a 259.9 a 497.6 a 569.5 ab l l2.6 a
I58 Aldicarb 33.9 a 307.0 ab 588.2 a 557.9 ab 3 I 4.2 c
I58 I,3-D 8 MIC 30.4 a 392.I ab 583.9 a 783.0 b I55.0 a
335 Check 34.5 a 255.0 a 459.9 a 445.I 0 I0 I .7 a
335 Aldicarb 30.2 a 357.2 ab 555.2 a 540.8 a 242.9 b
335 I,3-D 8 MIC 4I.6.a 435.0 b 575.9 a 723.5 a 245.9 b

 

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3

“Degree day accumulation base l0 C.

Column means followed by the same letter are not significantly different
. (P=0.05) according to the Student-Newmm-Keuls Multiple Range Test.

Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha
on May I, I978.

 

 

 

Table B4. Influence of selected management inputs on tuber number of potatoes

(cv Superior).

 

 

 

 

Treatment Tuber Number / Plant (grams)4
243%?" ”made 373.5 543.8 757.9 983.3
84 Check 7.I a' 7.3a ”J a I0.4a
84 Aldicarbz 5.5 a 8.7 a l2.3 a 9.9 a
84 l,3-D&MIC3 l0.l ab 8.9a II.4cI I0.6a
I58 Check 7.3 a 7.80 I0.5 a II.7 0
I68 Aldicarb 8.4 ab 9.0 a I00 0 I0.I 0
I58 I,3-D 8 MIC I2.4 b I0.5 a I0.3 a I0.3 a
336 Check 8.8 ab 6.9 a I0.0 a 8.7 a
335 Aldicarb I0.7 ab 9.0 a I M a 9.4 a
336 I,3-D & MIC I0.6 ab I0.2 a l I.9 a 9.2 a

 

 

 

lColumn means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 I/ha
on May I, I978.

“Degree day accumulation base I0 C.

APPENDIX C

168

Table C I. Influence of selected management inputs on foliage weight of
potatoes (cv Superior).

 

 

 

 

 

Treatment Foliage Weight (grams)4
[3'13ng 8 PSSIIC‘de 233.7 442.7 I005.4
0 Check 23.4 e' 2 I 5.I a 22.4 a
0 Aldicarbz 25.8 a 249.9 a 55.5 a
0 I,3-D 8 MIC3 20.8 a 278.3 ab 39.8 a
55 Check 23.9 a 274.2 ab 42.2 a
56 Aldicarb 20.0 a 263.8 ab 34.2 a
55 I,3-D 8 MIC 20.5 a 400.I b 40.7 0
I58 Check 23.I a 297.2 ab 49.3 a
I68 Aldicarb 22.8 a 397.6 b 74.0 0
I58 I,3-D 8 MIC 23.4 a 383.0 b 75.0 a

 

 

lColumn means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5-l/ha
on May I, I979.

“Degree day accumulation base I0 C.

 

169

Table C2. Influence of selected mmogement inputs on stem weight of potatoes
(cv Superior).

 

 

 

 

Treatment Stem Weight (grams)4
$33752?th Pesm‘de 233.7 442.7 723.2 I005.4
0 Check 0' 45.5 a 28.9 ab 8.I a
0 Aldicarbz 0 43.7 a 22.9 a I I.4 a
0 I,3-D&MIC3 0 47.3 a 27.9 ab l0.2 a
55 Check 0 35.9 a 39.I b 8.5 a
56 Aldicarb 0 43.0 a 37.2 ab 6.9 a
55 I,3-D 8 MIC 0 35.4 a 3 I.5 ab 82 a
I58 Check 0 45.0 a 25.5 ab I0.8 0
I58 Aldicarb 0 48.0 a 33.9 ab I20 0
I58 I,3-D 8 MIC 0 38.8 a 32.9 ab I2.5 a

 

Column means followed by the same letter are not significantly different

(P=0.05) according to the Student-Newman-Keuls Multiple. Range Test.

2Applied of planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3lnjected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 I/ha
on May I, I979.

4

Degree day accumulation base I0 C.

170

Table C3. Influence of selected management inputs on tuber number of potatoes

(cv Superior).

 

 

 

 

Treatment Tuber Number / Plant (grams)4
mfigfws PeSIICIde 233.7 442.7 723.2 I005.4
0 Check 0' I3.4 a II.2 a 7.0 a
0 Aldicarbz 0 I0.5 a 8.0 a 9.2 a
0 l,3-D&MIC3 0 I4.8 a I I.2 a 7.8 a
55 Check 0 9.2 a I2.0 a 9.4 a
56 Aldicarb 0 l I.2 a l3.4 a 7.4 a
55 I,3-D 8 MIC 0 I3.4 a I40 0 9.0 0
I55 Check 0 9.8 a 9.2 a 8.5 a -
|56 Aldicarb 0 I4.0 a I2.4 a 7.8 a

I55 l,3-D 8 MIC 0 7.8 a I28 0 8.0 a

 

IColumn means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3

on May I, I979.

4Degree day accumulation base I0 C.

Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha

171

 

 

 

 

Table C4. Influence of selected management inputs on plant weight of potatoes
(cv Superior).

Treatment Plant Weight (grams)4
Ph°sP“°ws Pesticide 233.7 442.7 723.2 I005.5
(kg/ho)

0 Check 27.0 e' 32 I.0 a 5I3.5 a 59I.7 a
0 Aldicarbz 30.5 a 33 I.3 a 555.2 a 9I0.2 a
0 I,3-D 8 MIC3 24.2 a 352.8 a 795.4 a 749.7 a
55 Check 28.2 a 345.8 a 554.4 a 85 I.7 a
55 Aldicarb 23.0 a 340.5 a 823.8 a 782.8 a
55 I,3-D 8 MIC 23.8 a 472.0 a 847.0 a 878.8 a
I58 Check 25.7 a 382.8 a 525.9 a 887.3 a
I58 Aldicarb 27.0 a 483.I a 790.I a 928.8 0
I58 I,3-D 8 MIC 25.7 a 459.8 a 859.2 a I030.7 a

 

lColumn means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha
on May I, I979.

“Degree day accumulation base l0 C.

172

Table C5. Influence of selected management inputs on tuber weight of potatoes
(cv Superior).

 

 

 

 

Treatment Tuber Weight / Plant (grams)4
$33752?“ Pesm‘de 442.7 723.2 I005.4
0 Check 45.7 e' 524.I a 55 I.9 a
0 Aldicarbz 24.1 a 532.2 a 822.2 a
0 I,3.D8MIC3 22.2 a 757.9 a 590.8 a
55 Check 2 I .0 a 50l.9 a 795.4 a
56 Aldicarb 2l.6 a 772.l a 734.I a
55 I,3-D 8 MIC 2 I.2 a 803.3 a 823.0 0
I58 Check 25.5 a 588.5 a 8l8.8 0
I68 Aldicarb 2 I.8 a 742.8 a 837.3 0
I58 I,3-D 8 MIC 24.3 a 8I3.3 a 934.5 a

 

lColumn means followed by the same letter are not significantly different

(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2

3
on May I, I979.

“Degree day accumulation base I0 C.

Applied of planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha

 

173

Table C6. Influence of selected mmogement inputs on root weight of potatoes

 

 

 

 

(cv Superior).
Treatment Root Weight (grams)h

Phosphorus . .

(kg /ha) Pesl’ICIde 233.7 442.7 723.2 I005.4
0 Check 3.6 a l3.7 a I2.5 a 9.3 a
0 Aldicarbz 3.8 a I3.5 a I I.8 a I I.0 a

’ 0 I,3-D 8 MIC3 3.4 a I5.0 a I0.5 a 8.9 a

56 Cheek 4.3 a l3.6 a I3.4 a I4.7 a
56 Aldicarb 3.0 a I2.2 a ”I.4 a 7.7 a
56 I,3-D 8: MIC 3.2 a l5.4 a I2.3 a 6.9 a

I68 Check 3.6 a I4.2 a I I.0 a 8.5 0

I68 Aldicarb 4.2 a I5.8 a l3.4 a 5.5 0

I68 I,3-D 8t MIC 3.3 a l3.7 a l3.0 a 7.6 a

 

lColumn means followed by the same letter are not significantly different

(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.
2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha
on May I, I979.

“Degree day accumulation base l0 C.

174

Table C7. Influence of selected mmagement inputs on population density of E.
metrans on potatoes (cv Superior).

 

 

 

 

Treatment _P_. penetrans per l00 cm3 soil
and per gram root tissue combined

$3732?“ Pesticide 233.7 442.7 723.2 I005.4
' 0 Check 39.8 d 75.8 b 255.4 be I33.5 a

0 AIdicdrb2 20.0 0 I30 a 9I.4 (lb 8.5 d

o I,3-D 8 MIC3 3 I.5 d 35.5 ab 285.0 be I I3.0 a
55 Check 38.8 d 35.5 ab 325.0 c 237.2 a
55 Aldicarb I5.5 a I70 (I 92.4 (lb 29.4 d
55 I,3-D 8 MIC 34.5 a 25.2 ab I52.0 abc 203.8 d
I58 Check 44.0 d 55.5 ab 255.4 be 254.4 a
I58 Aldicarb I4.8 a I3.5 d 34.8 d I4.0 d
I58 I,3-D 8 MIC 23.5 a 29.8 ab 293.0 be l89.2 d

 

'Column means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3

on May I, I979.

“Degree day accumulation base I0. C.

Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 I/ha

 

APPENDIX D

 

175

Table DI. Influence of selected management inputs on foliage weight of
potatoes (cv Russet Burbank).

 

 

 

 

Treatment Foliage Weight (grams)4

firms?” Pesticide 233.7 442.7 723.2 I I57.5

0 Check 8.8 e' l85.5 a 588.3 d 9I.4 a

0 AIdicdrb2 7.3 a 239.8 db 553.7 db 205.8 db

0 I,3-D 8 MIC3 8.5 5 258.2 db 779.0 db 289. I dbc
55 Check 7.3 a 239.5 (lb 558.5 Clb 222.8 eb
55 Aldicarb 4.9 d 249.4 (lb 803.2 db 408.3 abcd
55 I,3-D 8 MIC 5.8 a 330.4 c 980.8 db 55I.I ed
I68 Check 7.8 d 250.I ab 780.7 (lb 5I2.5 bed
I58 Aldicarb 7.7 a 259.7 db 889. I ab 489.I bed
I58 I,3-D 8 MIC 5.5 a 300.4 be I059.I b 577.3 d

 

Column means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 I/ha
on May I, I979.

“Degree day accumulation base l0 C.

176

Table D2. Influence of selected management inputs on stem weight of potatoes
(cv Russet Burbank).

 

 

 

 

Treatment Stem Weight (grams)£'
may“ Pesticide 233.7 442.7 723.2 I I57.5
0 Check 0' 39.3 d 28.9 d l6.5 a
0 AIdicdrb2 0 34.5 d 33.2 d 2 I.4 ab
0 I,3-D 8 MIC3 0 43.2 d 32.2 d 23.7 ab
56 Check 0 32.9 a 32.2 a 23.I ab
55 Aldicarb 0 33.4 d 33.5 d 27.0 ab
55 I,3-D 8 MIC 0 45.2 d 35.I d 34.I b
I68 Check 0 34.5 a 35.4 a 25.4 ab
I68 Aldicarb 0 27.3 d 37.5 a 27.0 ab
I58 I,3-D 8 MIC 0 43.8 d 44.9 d 35.5 b

 

lColumn mems followed by the same letter are not significantly different

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3

4Degree day accumulation base I0 C.

(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 I/ha
on May I, I979.

 

177

Table DB. Influence of selected management inputs on plant weight of potatoes
(cv Russet Burbank).

 

 

 

 

Treatment Plant Weight (grams)4
$32?“ Pesticide 233.7 442.7 723.2 I I57.5
0 Check I I.5 a 24I.0 a l036.5 a 946.6 a
0 AIdchrb2 9.4 a 294.7 db I I59.8 a l2l I.I ab
0 I,3-D 8 MIC3 I0.5 a 322.7 db mm d I485.5 ab
55 Check 9.I a 292.5 db I I22.I a I284.8 ab
55 Aldicarb 5.5 d 30I.9 db I274.4 d I49 I.5 ab
55 I,3-D 8 MIC 8.9 a 399.5 c I583.2 d 200l.0 b
I58 Check 9.5 a 303.3 db I259.I a I547.3 db
I58 Aldicarb I0.I a 304.3 Ob I4I2.2 d I5I3.7 db
I58 I,3-D 8 MIC 8.8 a 354.3 be I7 l0.5 a 20I5.2 b

 

 

 

lColumn means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 |/ha
on May I, I979.

 

“Degree day accumulation base I0 C.

178

Table D4. Influence of selected management inputs on tuber number of potatoes
(cv Russet Burbank).

 

 

 

 

Treatment Tuber Number / Plant (grams)a
me?” Pesticide 233.7 442.7 723.2 I I57.5
0 Check 0' 8.8 d I4.0 d I2.0 d
0 AIdicdrb2 0 4.8 a I7.0 d 9.2 d
0 I,3-D 8 MIC3 0 I I.0 d I8.5 d I4.0 a
55 Check 0 5.4 d 20.0 d I2.5 d
55 Aldicarb 0 4.5 d I7.0 d I I.0 d
55 I,3-D 8 MIC 0 5.2 a 24.0 d I7.2 5
I58 Check 0 2.5 a 22.0 a I I.0 '5
I58 Aldicarb 0 3.2 8 I98 0 I I.8 0
I58 I,3-D 8 MIC 0 5.2 d 24.8 d I5.4 d

 

IColumn means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman—Keuls Multiple Range Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 I/ha
on May I, I979.

“Degree day accumulation base l0 C.

Table D5.

(cv Russet Burbank).

179

Influence of selected management inputs on tuber weight of potatoes

 

 

 

 

Treatment Tuber Weight / Plant (grams)4
m2?“ Pesticide 233.7 442.7 723.2 II57.5
0 Check 0' I.5 a 400.9 Cl 822.I a
0 Aldicarb2 0 0.7 a 453.7 a 958.3 0
0 I,3-D 8 MIC3 0 2.7 a 497.5 a I I55.4 d
56 Check 0 I.4 a 400.7 a I025.2 a
55 Aldicarb 0 I.7 a M 5.9 d I035.2 d
55 I,3-D 8 MIC 0 2.5 O 548.3 d I385.5 0
I58 Check 0 0.3 a 424.7 a I092.7 5
I58 Aldicarb 0 0.9 a 454.8 d I075.5 0
I58 I,3-D 8 MIC 0 0.7 a 583.2 a l282.0 a

 

IColumn means followed by the same letter are not significantly different

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

(P=0.05) according to the Student-Newman-Keuls Multiple Range Test.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha

on May I, I979.

4Degree day accumulation base l0 C.

180

Table D6. Influence of selected management inputs on root weight of potatoes
(cv Russet Burbank).

 

 

 

 

 

Treatment Root Weight / Plant (grams)"
ma?” Pesticide 233.7 442.7 723.2 I I57.5
0 Check 2.5 a' I4.8 0 I84 a I5.7 a
0 Aldicarb2 2. I a I9.5 a l9.2 a I5.7 a
0 I,3-D 8 MIC3 2.0 a I8.5 a I9.0 a l7.4 a
55 Check I.8 a I8.8 a 20.5 a I3.7 a
56 Aldicarb I.6 a I7.3 a 20.6 a 2 I.0 a
55 I,3-D 8 MIC 2.l a 20.5 a I8.0 a 20.2 0
I58 Check I.7a l8.5a I8.3o l6.6a
I68 Aldicarb 2.4 a I6.5 a 20.7 a 2 I.2 a
I58 I,3-D 8 MIC 2.2 a I9.4 a 23.3 a 20.4 a

 

IColumn means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newmm-Keuls Multiple nge Test.

2Applied at planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 I/ha
on May I, I979.

“Degree day accumulation base l0 C.

181

Table D7. Influence of selected management inputs on population density of E.
aetrans on potatoes (cv Superior).

 

 

 

 

Treatment _P_. penetrans per l00 cm3 soil
and per gram root tissue combined

my“ Pesticide 233.7 442.7 723.2 I I57.5

0 Check 3 I.2 ab' 52.5 ab 99.2 5 I534 b

0 Aldicarb2 7.5 a I5.4 a 9.0 a 7.0 a

0 I,3-D 8 MIC3 50.8 a 5 I.8 ab I02.4 a I75.0 b
55 Check 24.5 ab 78.8 b 9 I.4 a 99.8 b
56 Aldicarb 8.4 a 7.8 a 24.6 a 3.2 a
55 I,3-D 8 MIC 32.5 ab 4I.5 ab 60.8 a I27.4 b
I58 Check 29.4 ab 43.4 ab 70.0 a I50.8 b
I58 _ Aldicarb 8.5 a I3.4 a I9.2 a I3.8 a
I58 I,3-D 8 MIC 29.0 ab 55.5 ab 73.4 a I52.2 b

 

lColumn means followed by the same letter are not significantly different
(P=0.05) according to the Student-Newman-Keuls Multiple nge Test.

2Applied of planting in the fertilizer furrow at a rate of 3.4 kg a.i./ha.

3Injected on a broadcast basis to a soil depth of 20 cm at the rate of 93.5 l/ha

on May I, I979.

“Degree day accumulation base I0 C.