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1 LEE RAfiY
. Micki} gar fitmtfi

University

 

This is to certify that the

thesis entitled

Plant Parasitic Nematodes
Associated With Field Corn
(Zea maxs L.) in Michigan

presented by

Edward P. Caswell

has been accepted towards fulfillment
of the requirements for

Masters degreein Entomology

mm

Major professor

 

February 26, 1982
I)ate

 

0-7639

Ill 1 ill 1 Illlllllllllllllllllfllll L

3 1293 00987 5075

 

 

 

 

 

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PLANT PARASITIC NEMATODES ASSOCIATED WITH FIELD CORN
(A32 mazs L.) IN MICHIGAN

By

Edward P. Caswell

A THESIS

Submitted to
Michigan State University

in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Botany and Plant Pathology

I982

ABSTRACT

PLANT-PARASITIC NEMATODES ASSOCIATED WITH
FIELD CORN (Z_e_a_ mazs L.) IN MICHIGAN

By

Edward P. Caswell

An extensive survey of plant parasitic nematodes associated with
commercial field corn was carried out during the summer of I979. Thirty-eight
counties were selected as survey sample sites, and 0.0l% of Michigan's 2.8

million acres of field corn was sampled. The nematodes found with greatest
frequency were Pratylenchus spp., with 98% of the samples collected containing

this genus. Populations as high as |,096 Pratylenchus spp./gram of fresh root

 

were observed. Tylenchorhynchus spp. were observed in 3|% of the samples
collected. Other plant-parasitic genera observed include: Paratylenchus spp.,
Tylenchus spp., Criconemoides spp., Helicotylenchus spp., and Heterodera spp.
The absolute frequencies, relative densities, and prominence values for several
of the predominant genera were calculated on a regional basis. Coefficients of
association between nematodes within regions yielded no recurrent specific
associations between species. There was no obvious relationship between

nematode population densities md soil type.

During the summer of I980 three nematode population management trials
were conducted at three different field locations. Although some of the selected
control methods were significantly effective in controlling nematode
populations, significant differences in yield which could be attributed to

nematode damage were not observed.

DEDICATION

This thesis is dedicated with love and respect to Ms. Robin Rosenbaum,

without whose love cnd patient understmding the completion of this work would

have been additionally arduous.

1'1

ACKNOWLEDGMENTS

I wish to express my appreciation to Dr G. W. Bird for serving as my major
professor during the course of this work, and for his guidance in the preparation
of this manuscript. Thanks also to the members of my guidance committee: Dr.
Winston Fulton, Dr. L. Patrick Hart, Dr. E. C. Rossman, and Dr. R. F. Ruppel.

Thanks to friends and colleagues who helped to make the time spent
educational and enjoyable; Annette KIeineke-Borchers, An MacGuidwin, Dave
Miller, Ken Milne, Joe Noling, Hans Olsen, Jim Pieronek, Lindy M. Rose, Dr. I.
J. Thomason, md last but not least, Fred A. Warner.

A special thanks goes to "Dr." John Davenport, who couldn‘t have known
what he was getting into. His technical advice md touch of patience contributed
immeasurably to the completion of this work.

A special debt of gratitude is owed the Michigm State University
Department of Entomology for both finmcial support and access to their
excellent facilities. Dr. James Bath has duly earned his reputation as an
excellent chairperson, and I wish to thank him for making me feel at home in the
department. During my stay with the Entomology Department, I have
assimilated a philosophy of science and life which I could not have obtained
elsewhere.

The contribution of the Michigan State University Cooperatve Extension
Service to the completion of this thesis is considerable. I am grateful for their
help.

Last, thanks to my parents, Dr. and Mrs. H. H. Caswell, and family for

their support and encouragement.

iii

Introduction ........................ 1
Literature Review ..................... 2
A. Field Corn Production .................. 2
l- Hybridcorn . . . . . .1 ............. 3
2- Michigan field corn ................. 7
B. Nematodes Associated With Field Corn Production ..... 8
I. Pratylenchus spp. ................. 8
2. Tylenchorhynchus spp- ............... 13
.3. Xiphinema spp. .................. 14
4. Meloidgzne spp- ................. 15
5. Longidorus spp- .................. 15
6. Heterodera spp. .................. 16
7. Belonolaimus spp. ................. 16
8. Other nematodes ................. 16
C. Ecology of Plant Parasitic Nematodes ,,,,,,,,,,, 18
I. Soil parameters .................. 18
.2. Community ecology ................ 20
D. Nematode Population Management ............ 24

TABLE OF CONTENTS

 

 

 

iv

TABLE OF CONTENTS, continued

IV.

VI.
VII.
VIII.

Materials md Methods ................... 29
A. Michigm Field Corn Survey ............... 29
B. Nematode Population Mmagement Trials ......... 39
I. Hal Benn corn production site ............ 39
2. Floyd Baum corn production site ........... 41
3. Alan Cable corn production site ........... 43
Results ......................... 45
A. Michigan Field Corn Survey ............... 45
B. Nematode Population Management Trials ......... 54
I. Hal Benn corn production site ............ 54
2. Floyd Baum corn production site ........... 55
3. Alan Cable corn production site ,,,,,,,,,,, 57
Discussion .................. ' ...... 78
A. Michigm Field Corn Survey ............... 78
B. Nematode Population Mmagement Trials ......... 84
Summary ......................... 106
References Cited ..................... 107
Appendices ....................... 120

Table I.

Table 2.

Table 3.

Table 4.

Table 5.

Table 6.

Table 7.

Table 8.

Table 9.

Table I0.

Table l l.

LIST (1" TABLES

Pesticides applied at Hal Benn corn production
site in Jackson County . ......... . ..... 40

Pesticides applied at Floyd Baum corn
production site in Jackson County . , ,,,,,,,,, 42

Pesticides applied at Alan Cable corn production
site in Clinton County . . . . . ..... . ..... 44

Pratylenchus spp. and Tylenchorhynchus spp.
populations recovered from I52 field corn
production sites in Michigm. . . . . ......... 46

Prominence values of eight nematode taxa
associated with six field corn production regions
in Michigm (Fig. 3) ................. 49

Relative frequencies of eight nematode taxa
associated with six field corn production regions
inMichigmlFig.3)................. 50

Coefficients of association for statistically
significant combinations of plant-parasitic
nematodes found during the I979 field corn
survey of Michigan ..... . . . ......... 51

coefficients of association among plant-parasitic
and predaceous taxa found during the I979 field
corn survey of Michigm ............... 52

Coefficients of association for statistically
significant combinations of plant parasitic
nematodes found during the I979 field corn
survey..............

Populat'on density of Pratylenchus penetrms per
IOO cm of soil at the Hal Benn corn production

site.............. .......... 62

Population densities of Pratylenchus penetrans
per gram of root at the Hal Benn corn production
site........

vi

 

 

LIST

Tab!

Tab

Tab

Tat

Tat

Tat

LIST OF TABLES, continued

Table I2.

Table I3.

Table l4.

Table I 5.

Table I6.

Table I7.

Influence of five pesticides on corn height at the
Hal Benn corn production site. . . . . . . . .

Population density of Pratylenchus penetrans per
I00 cm3 soil at the Floyd Baum corn production
Site. 0 O I O O O O O O O O O O I O O O O 0

Population densities of Pratylenchus penetrans
per gram of corn root tissue at the Floyd Baum
corn production site. . . . ...... . . .

Population density of PratJIenchus etrans per
l00 cm3soil at the Alan Cable corn prmtion

Site. 0 O I O O O O O O ...... O O O 0

Population densities of Pratylenchus penetrans
per gram of root at the Alan Cable corn
productionsite...............

Absolute frequencies, absolute densities, relative
densities and prominence values of four common
plant parasitic nematode genera associated with
Michigan field corn . . . . . ........

vii

Figure I.

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Figure 6.

Figure 7.

Figure 8.

Figure 9.

Figure I0.

Figure l I.

LIST 0" F IGlRES

Field corn production in Michigan. Total acres
harvestedversustime. . '. . . . . . . . . .

Field corn production in Michigan. Average
yield (bu/A) versus time , , , , , , , , , , ,
Counties sampled during the I979 Michigan field
corn survey, grouped into 6 geographic regions

Counties sampled during the I979 survey , ,

Cumulative degree days (base I0°C) as
calculated from April I, I980, to the sampling
date specific for each county included in the
Michigan field corn survey ..... . . . . .
Soil types for low population densities of
Pratylenchus spp. as recovered during the I979
field corn survey plotted on a soil textural
triangle. . . . . . . .......... .

Soil types for high population densities of
Pratylenchus spp. as recovered during the I979
field corn survey plotted on a soil textural
triangle. . . . . .............

Soil types for low population densities of
Tglenchorhynchus spp. as recovered during the
I field corn survey plotted on a soil textural
trimgle ..................
Soil types for high population densities of

Iylenchorhynchus spp. as recovered during the
I979 field corn survey plotted on a soil textural

"imgle. 0 O O O O O O O O O O O O O O O O O O O 0

Soil types for high population densities of
HelicotLIenchus spp. as recovered during the
I979 field corn survey plotted on a soil textural
triangle..................

Soil types for high population densities of
Paratylenchus spp. as recovered during the I979
field corn survey plotted on a soil textural
triangle .............. . . . .

viii

..... 10

..... 58

..... 60

LIST OF F IGLRES, continued

Figure I2.

Figure I3.

Figure Ill.

Figure IS.

Figure l6.

Figure l7.

Figure l8.

Figure I 9.

Figure 20.

Figure 2|.

Figure 22.

Shelled grain yield versus root population
density of Pratylenchus penetrans at harvest

for the Alan Cable corn production site. . . . . . . .

Shelled grain yield versus root and soil
population density of Pratylenchus penetrans at

harvest for the Alan Cable corn production site , . , . .

Shelled grain yield versus root population
density of Pratylenchus metrans at harvest

for the Hal Benn corn production site . . . . . . . .

Shelled grain yield versus root md soil
population density of Pratylenchus penetrans at

harvest for the Hal Benn corn production site . . . . . .

Shelled grain yield versus root population
density of Pratjlenchus penetrans at harvest

for the Floyd Baum corn production site , , . , . . .

Shelled grain yield versus root and soil
population density of Pratylenchus penetrans at

harvest of all three corn production sites. . . . . . . .

Pratylenchus wetrans population density
fluctuations per gram of root relative to
pesticide application at the hol Benn corn

prOdwtim Site 0 O O O O O O O O O O O O O O O

Pratylenchus wetrans population density
fluctuations per I00 cubic centimeters of soil
relative to pesticide application at the Hal

Benncornproductionsite . . . . . . . . . . . . .

Pratylenchus penetrans population density
fluctuations per gram of root relative to
pesticide application at the Alan Cable corn

prOdUCtim Site. 0 O O O O O O O O I O O I O O

Pratylenchus enetrans population density
fluctuations per l00 cubic centimeters of soil

relative to pesticide application at the Alan

Cable corn production. site. . . . . . . . . . .

Pratylenchus penetrans population density
fluctuations per gram of root relative to
pesticide application at the Alan Cable corn

productionsite............ ......

ix

72

72

74

74

76

76

88

88

91

91

93

LIST (I: FIGURES, continued

Figure 23. Pratylenchus enetrans population density
fluctuations per I00 cubic centimeters of soil

relative to pesticide application at the Alan
Cablecornproductionsite. . . . . . . . . . . . . . . 93

Figure 24. Pratylenchus wetrans population density
fluctuations per gram of root relative to
pesticide application at the Alan Cable corn
Productionsite................... 95

 

Figure 25. Pratylenchus afietrans population density

fluctuations per cubic centimeters of soil
relative to pesticide application at the Alan
Cable corn production site. . . . . . . ........ 95

Figure 26. Pratylenchus metrans population density
fluctuations per gram of root relative to
pesticide application at the Floyd Baum corn
Productionsite................... 98

Figure 27. Pratylenchus etrans population density
fluctuations per ILW cubic centimeters of soil
relative to pesticide application at the Floyd

Baumcornproductionsite. . . . . . . . . . . . . . . 98

Figure 28. Pratylenchus wetrans population density
fluctuations per gram of root relative to
pesticide application at the Floyd Baum corn
productionsite............. ...... 102

 

Figure 29. Pratylenchus fletrans population density
fluctuations per I00 cubic centimeters of soil
relative to pesticide application at the Floyd
Baumcornproductionsite. . . . . . . . . . . . . . .102

Figure 30. Cumulative precipitation versus degree day
accumulation at the Hal Benn corn production
Site I O O O O O O O O O O O O O O O O O 0 O O O O O 105

I. INTRODUCTION

Corn is an agricultural crop of greatworldwide importance. In recent
decades various technical advances in agriculture have resulted in corn yields
that previously would not have been possible. The effective economical control
of pests associated with yield loss has been a major contributing factor to these
increased yields. One component of this associated pest complex is in itself a
complex: plant parasitic nematodes. Decreased corn yields associated with high
population densities of these nematodes have received an increasing amount of
attention in recent years. Relatively little, however, is known about nematodes
associated with field corn production systems in Michigan.

The purpose of this research was to determine what plant parasitic
nematodes are associated with Michigan field corn production, and whether
population densities typically observed result in decreased yields under Michigan
field conditions. The project consisted of two parts: a statewide field corn
survey and nematode control evaluations. Thirty-eight counties in Michigan's
corn producing regions were sampled for plant parasitic nematodes. Field plot
studies were performed to evaluate the efficacy of various nematicidal

materials, and their effect on yield in relation to nematode control.

II. LITERATURE REVIEW
A. Field Corn Production

I. Hybrid corn

Corn (Leg ESE L.) is considered indigenous to the western hemisphere.
The first historic records of corn production date back to I492, when Europeans
arrived in the western hemisphere. Columbus discovered that the native Indims
depended on corn for much of their sustenance. Explorers of the New World
named the plant "maize," and by I495 it had been distributed widely throughout
Europe (Jugenheimer I976, Sprague I977). There are several hypotheses about
the origin of corn. How long corn has been grown md where it came from,
however, are still unresolved questions. Each hypothesis attempts to explain the
probable mcestry in terms of related plant species. Three possible type
ancestors of corn are teosinte, tripascum, md wild maize. These plants are
suggested as possible representatives of the phylogeny involved in the evolution
of corn (Mangelsdorf I974). These species are found in areas of Central and
South America.

Corn was one of the first plant species used by neolithic humankind as m
agricultural crop. Americm Indims cultivated several strains of wild corn
(Poehlmm I977). Through selection, they produced a number of different types,
including flint, flour, pop, md sweet corn. Most of today's field corn varieties
originated with the flint and flour types. These were the preferred types utilized
by the lndims and the early settlers of the U.S. (Wallace and Brown I956). Corn
was instrumental in the geographical expmsion md development of the U.S.
(Sprague I977). Modern commercial field corn, however, is not capable of

survival in the wild. Maize is an important component of the diet of a

significant portion of the current world population.

Corn is a monoecious grass. It has a staminate infloresence (tassels)
distinctly separate from the pistils; however, exceptions occur in wild strains.
Each female flower contains a single ovary with a long style. The silk is
receptive to pollen along its entire length. It functions morphologically as both a
stigma and style. Fertilization occurs when pollen lands on the silk (Poehlman
I977). The pollen tube emerges md transports the pollen sperm nuclei to the
ovule. Double fertilization occurs when the female nuclei in the ovule are
fertilized by the two male nuclei, resulting in the endosperm and embryo. This
process is typical of angiosperms.

In I909 Dr. G. H. Shull reported that open-pollinated field corn was a
composite of many different complex hybrids which decline in vigor with
inbreeding. Shull suggested that plant breeders should maintain as many hybrid
combinations as possible. He recognized that inbreeding resulted in decreased
vigor, and that subsequent hybridizing of two inbreds would result in a return to
the vigorous condition (Wallace and Brown I956). If inbred plants were
maintained long enough, the resulting hybrids would yield more uniform stmds
(Poehlman I977). Dr. Edward East of the Connecticut Agricultural Experiement
Station noted a similar phenomena. At this time it was believed that production
of hybrid corn would not be economically feasible because of the costs of
maintaining poor-yielding inbred lines. In I9I8, Jones md East suggested that
crossing two single cross hybrid stains would result in a double cross strain and a
good yielding plant (Wallace md Brown I956). This would be more economically
feasible because the two single crosses used to produce the double cross would be

vigorous plants (Wallace and Brown I956). Many inbreds were developed during

the I920$ md I9305. The inbreds were combined into single md double cross
hybrids for use in the U.S. corn belt.

Hybrid corn is the first generation resulting from the cross between two
inbred lines. Inbred lines of corn are developed by self-fertilization and the
continuous selection of acceptable progeny (Jugenheimer I976). A reduction in
vigor occurs with inbreeding. Progeny with desirable characteristics are
maintained, and continue to be inbred. The genotype is maintained, and
deleterious recessive characteristics can be eliminated. This results in relatively
homozygous plants after 5-7 generations of controlled self pollination. Once
inbred lines are obtained, one is chosen as the seed-bearing parent for the cross.
A good pollen producer is chosen as the pollen donor. The female parent is
detassled and pollinated by the pollen-bearing inbred (Poehlman I977). This is a
single cross. Single cross seed may be planted by field corn growers. Uniform
plant stands md high grain yields result from the uniform genetic composition of
the seed.

A number of multiple crosses are possible for the production of hybrid corn
seed. A modified single cross is made when the progeny of two related inbreds
are used as one parent, and m unrelated inbred is used as the other parent.
Three-way crosses result from crossing single cross lines with an inbred line.
This results in corn with a diverse genetic background. The double cross is a
solution to the problem of economics in raising hybrid corn. It is the result of a
cross between two single crosses (Poehlman I977). Because of the resulting
uniform, high-yielding plants, modern corn breeding has placed significant
emphasis on the development of the single cross.

Few developments in plant breeding have received more accolades, or been

 

ace:
vigc
lo .
i09
hel
of '
hyt
vig

IH

P“

88

St

accepted more widely than hybrid corn. Hybrid corn has resulted in increased
vigor, termed heterosis or hybrid vigor. Two explanations are generally offered
to explain hybrid vigor. The first is that hybrid vigor results from bringing
together favorable dominant genes from the parents. The second theory is that
heterozygosity is more vigorous than homozygosity (Jugenheimer I976). Neither
of these hypothesis satisfactorily explains all cases of hybrid vigor. Most often,
hybrid corn breeders look for increased vegetative growth or grain yield. Hybrid
vigor, however, may be displayed in other ways. Plant breeders use gene
recombination as the principle tool in the search for improved crop varieties.
Gene recombination is the basis for the development of present plant breeding
procedures. Unbeknownst to the Indims md early settlers of the U.S., this is
essentially what their selections achieved.

Detasseling is m important component of the hybrid corn production
system. This is a labor-intensive process. During the l9SOs, utilization of a
male cytoplasmic sterility factor and the fertility-restoring breeding system
eliminated the need for detasseling. Plants chosen as the seed parent lack a
fertility restoring gene, and no pollen is produced. These plants are then crossed
with one that has the proper fertility-restoring factor (Poehlman I977). The
resulting progeny are then fertile. The "Texas Cytoplasmic Sterility Factor" was
identified as the most dependable form of the male sterility cytoplasm. The
genes necessary to restore fertility to the hybrid plant were very effective when
Texas cytoplasmic male sterility was bred into the seed parent.

Problems resulting from reliance on particular varieties with specific
genetic constitution was dramatically emphasized in I970 when a mutant strain

of the southern corn leaf blight fungus reached epidemic proportions in the

central U.S. corn belt. It was discovered, however, that strains with the Texas
cytoplasm were very susceptible to a new strain of Helminthosporium maflis
(Horsfall and Cowling I978). In I970, the race of the southern corn leaf blight
fungus spread throughout the southern and central U.S. corn belt. Since 90% of
the corn planted in this area contained the Texas genes these hybrids were
extremely susceptible. Fifteen percent of the nation's crop was lost (Horsfall
and Cowling I978). Breeders returned to the practice of detasseling until
different sources of cytoplasmic male sterility could be used in hybrid
production. Alternate sources were found and used, but not to the exclusion of
detasseling. Seeds produced by detasseling were planted together with seeds
produced using cytoplasmic sterility. This provided the germplasm diversity so
that fields would not be planted with a population of plants which were
genetically homogeneous for a particular cytoplasmic factor.

Selection for favorable traits and characters has resulted in the elimination
of some components of the corn gene pool. In some cases the germplasm
resources that have been eliminated due to undesirable characteristics are lost
to hummkind. These may represent a source of potential variation needed in the
future.

The concern over dwindling availability of sources of gene variation
resulted in a collection expedition in I943 by scientists of the Rockefeller
Foundation, USDA, and Mexicm Department of Agriculture to identify and
collect native varieties of corn in Mexico. More than l2,000 collections were
made. The corn obtained from these collections was grouped into several
different races on the basis of recognizable characters such as tassel, ear,

physiological, cytological, md genetic differences (Jugenheimer I976).

Throughout the years 01 extensive diversity of corn has been collected from all
over the world. It is stored at the International Maize and Wheat Improvement
Center (ICMMYT) in Mexico.

Corn is the leading grain crop in the United States, with an mnual metric
ton production about 2.5 times that of wheat, the next leading cereal grain.
From a world perspective, corn is the third leading cereal crop, after wheat cnd
rice. The U.S. produces nearly half the world's field corn (Poehlman I977). Corn
is used in the US primarily as feed for livestock, and it is a source of industrial
products. In recent years attention has been given to field corn as a source for
alcohol to be used as a fuel additive in combination with gasoline. There are
numerous other industrial uses for field corn (Sprague I977). Corn is still of
primary importance as a food grain in many areas of the world, including Mexico,
Central America, parts of South America, China and Africa.

Overall, the production of hybrid field corn is a complex process in which
numerous desirable characteristics are necessarily selected. The complexity of.
the process is compounded by the variety of conditions under which field corn
production occurs. Corn is grown in many geographical areas of the world at
various latitudes. Different cultivars are required for the long growing seasons

of southern latitudes, and the short growing seasons of northern latitudes.

2. Michigan Field Cam
In Michigan, field corn is grown annually on approximately three million
acres. An average yield of 80 bushels per acre and an average price of $2.50 per
bushel represents 01 mnual revenue of approximately 500 million dollars. In

I979, field corn production ranked first among all field crops, and third among

all major crops md livestock products produced in Michigan (Mich. Dept. Agric.
I979). The annual acreage of three million for grain and silage corn consistently
ranks Michigm among the top ten corn-producing states in total acreage
harvested (Fig. I). In I973 and again in I977, national individual corn yield
records were set in Michigan (Michigan Dept. of Agriculture I979). Michigm
corn growers harvested 0 record 238 million bushels in I979, an amount 20%
above the record set in I977 (Michigan Dept. of Agriculture I979). In I979,
average yield reached a high of 95 bushels per acre (Fig. 2).

The corn production system is complex. The equipment, fertilizer, md
pesticides required to raise a corn crop in the U.S. mmdates a sizeable economic
investment. The modern corn grower is interested in achieving the highest profit
possible with the given land, environmental, and monetary constraints within
which he must operate. It is in this regard that the management of plant

parasitic nematodes associated with field corn production has become a concern.

B. Nematodes Associated with Field Corn Production

Seven different genera of plant parasitic nematodes are believed to have
detrimental impacts on corn production. Most of these are relatively non-
specific in relation to host range (Barker I978, Ferris and Bernard I97l, Johnson
md Nusbaum I968). An exception to this generalization is Heterodera zeae.

l. Pratylenchus spp.

Root-lesion nematodes (Pratylenchus spp.) were one of the first plant
parasitic nematode species reported associated with the roots of diseased field
corn in the U.S. In I9SI, stunted corn plants were found in smdy soils in Texas,

and Pratylenchus spp. were identified as the cause of poor growth (Young l95l).

Figure I. Field corn production in Michigan. Total acres harvested
versus time. ~

Figure 2. Field corn production in Michigan. Average yield (bu/A)
versus time.

10

 

FICRESI THOUSHNDS I

 

HISTORIC DATA
Cam in Michigan - Total Acres Harvested

2‘00

I‘M

 

 

 

 

 

YIELD BU/Fl

 

a V 5 v I ' I T T '7 T
IIIII 1m 1”. (“I I“ I!“ 18.5
YERR
5i

HISTORIC DATA

Cam in Michigan

 

 

 

a - I . T I f r - r
"I. I... 1”. I” 1'“ I“. am

YERR

 

 

 

11

A large area of plants 6 to 36 inches in height were surrounded by stalks almost
twice that height. Stunted stalks were easily pulled from the soil. The root
systems were underdeveloped with swollen root tips. Pratylenchus spp. present
at this site caused lesions on the basipetal and acropetal areas of the roots
(Young I953).

Species of Pratylenchus associated with corn include: E. brachzgrus, E.
me, E. @etrans, E. crenatus, E. m E. hexincisus, _P_. scribneri, E. ‘L'IELI:
and E. Mei (Endo I959, Miller 3 a_l. I963, Dickerson fl g_l_. I964, Young I964,
Townshend I972, Johnson md Chalfant I973, Egunjobi I974, Norton and Hinz
I976, Smolik I978, Bergeson I979, MacDonald I979, Riedel g a_l. I979). Corn is
an excellent host for Pratylenchus brachyurus and _P_. ZGIJ (Endo I959).
Populations of _P_. brachm. rus increase significantly under maize production
(Ejunjobi I974, Brodie and Murphy I975). Populations of E. hexincisus were
found in corn fields in Minnesota and Ohio (MacDonald I979, Riedel et al. I979).
E. hexincisus has also been found associated with corn plants in Indiana, and the
upper midwest of the U.S. Root populations of E. hexincisus as high as 33,000-
ll7,000 per gram dry root have been reported (Norton md Hinz I976, Bergeson
I980).

E. Metrans was reported as associated with corn root problems in New
York, and Pratylenchus spp. were found to be the nematodes most commme
associated with field corn in that state (Miller _t_ 91. I963). Severe damage was
observed in fields with these nematodes present at relatively high population
levels. P. penetrans md E. crenatus were found in corn fields in Ohio (Reidel Q
51. I979). E. penetrans and E. M have been reported in Ontario soils and
have been found infecting corn roots (Townshend I972). In pathogenicity studies,

12

com roots, stalk height, and stalk diameters were found to be reduced by _P_.
@etrans (Dickerson Q 91. I964). E. z_egg is limited to the southeastern U.S. It
is present as far north as Kentucky and southern Pennsylvania (Norton I978). E.
scribneri has been found in many different areas of the U.S. Included in its range
are California, and the southeastern U.S., Illinois, Indiana, and north into
Minnesota and North Dakota (Norton I978, Smolik I978). Although it has been
found in eastern New York State, it has not yet been found in Ohio.

Symptoms of Pratylenchus infection have been observed in the field. The
typical symptoms of root-lesion nematode infestation include stunted shoot
growth, yellowing of leaves, wilting, reduced yields, and stunted root systems
(Young I95I, I953, Graham I954). The root-lesion nematode deposits its eggs in
the roots of corn. Observations by Graham (I954) on the damage caused by this
nematode indicate that on corn it fails to produce characteristic well-defined
lesions often found on other crap hosts. Instead, water-soaked areas were
observed as typifying the infection sites of this nematode on corn. These
observations differ from the lesions observed by Young (I953).

The use of nematicides in Iowa for control of E. hexincisus has increased
corn yields as much as 26% (Norton I978). After nematicide applications in l6
experiments in Iowa, yields were increased in plots treated with nematicides
versus untreated plots by 2l%. These yields were negatively correlated with
population densities of Pratylenchus spp., Helicotylenchus spp. and others. In
Indiana nematicide tests, 85-98% control of Pratylenchus spp. by the use of
nematicides increased corn yields by as much as I2-l4% (Norton I978).

In some evaluations, populations of Pratylenchus spp. have not decreased

 

yield. Population studies of E. hexincisus on field corn under greenhouse

13

conditions did not result in significant differences between nematode-infested
plants and non-infested plants (Norton I979). In Minnesota, field plots were
established to determine the effects of E. hexincisus on field corn. Over a
period of three years, no significant differences caused by nematodes were found
(MacDonald I979). In Ohio, field trials at several locations failed to correlate E.
Egetrans or E. hexincisus populations with significant corn yield loss at common
Ohio field population densities (Riedel e_t_ a_l. I979). In lndicna, E. hexincisus
populations at high levels (33,000-l l7,000 per gram dry root weight) failed to
cause significant decrease of shoot weight md length, or root weight (Bergeson
I980). These results suggest that stress plays an important role in the
development of Pratylenchus-induced grain yield reduction in com. If
environmental conditions are favorable for plant growth, the number of

Pratylenchus spp. necessary to result in disease symptoms may be increased

 

(Barker I978, Zirakaparzar e_t a_l. I980).

It has been noted that the feeding and other behavioral activities of
Pratylenchus spp. infesting corn roots provide an improved root environment for
other disease-causing organisms (Christie I959, Miller e_t 91. I963). In New York,
various fungi have been isolated from the roots of corn in areas where stunted
growth was observed. In addition, populations of Pratylenchus spp. were found at
these sites. It was concluded, however, that no single one of the organisms

isolated from the corn roots in the area was capable of causing the severe

damage observed (Miller g a_l. I963).

2. leenchorhynchus spp.
Tobacco stunt nematode (leenchorhynchus claytoni) has been reported

associated with field corn in North Carolina and other areas of the U.S. (Graham

14

I954, Nelson I956, Griffen I964, Barker I974). I. clafloni is regarded as a weak
pathogen on field corn (Hornby and Ullstrup I967). Tylenchorhynchus maximus
also parasitizes corn. It resulted in stunting of field corn in greenhouse studies
(Griffen I964).

Greenhouse pathogenicity studies with populations of Michigm
Tylenchorhynchus nudus failed to produce any significant decrease in corn
growth (Rose, unpub. data). It is generally concluded that com plants cm
withstand high populations of Tylenchorhynchus spp., especially as the plants
grow older md develop more extensive root systems. Thus, if this nematode
causes serious problems in corn production, high populations must be present
early in the growing season (Nelson I956). The histopathology of corn roots
exposed separately to Fusarium roseum or Pithium ultimum in monoxenic
culture, and also that of dixenic cultures containing 1. claytoni indicated that
the fungi were the primary pathogens. 1. claytoni did not serve as a
predisposition agent for the fungi, or increase the severity of the disease (Kisiel

t a_I. I969).

3. Xiphinema spp.

The dagger nematode (Xiphinema spp.) was among the first nematodes
found associated with corn in the U.S. The dagger nematode has a very wide
geographic distribution. It has been found associated with corn in Kentucky,
Wisconsin, Texas, Georgia, North Carolina, Iowa, Michigan, Indiana, Illinois, and
North Dakota (Chapman I954, Griffen I964, Young I964, Barker I974, Johnson
et al. I975 8: I978, Norton flfl- I978, Smolik I978, Thomas I978). Conflicting
reports have been published concerning the degree of susceptibility of field corn

15

to this nematode, and the suitability of corn for Xighinema spp. reproduction.
Research has shown that populations of M. americanum remain relatively low on
corn (Johnson a ll. I975). Other reports have indicated that Xiphinema
populations increase relatively well on corn, and occur in high densities in field
corn production sites (Barker I974). Overall, relatively little is known about the

effect of Xiphinema spp. on field corn (Norton I978, Norton e_t a_l. I978).

4. Meloidogyne spp.

Root-knot nematodes (Meloidogyne spp.) are frequently associated with
field corn in the southeastern U.S. (Baldwin and Barker I970a, Baldwin and
Barker I970b). M. arenaria, M. incgggita, and M. iavanica reproduce at varying
rates on field corn (Baldwin and Barker I970a, Johnson g _c_I_I_. I974, Johnson I975,
Baldwin at El. I970). Corn is not a suitable host for Meloidogyne _hgpl_a
reproduction. Two biotypes, however, of M. llqpla have been reported to
reproduce on corn. These biotypes were found in Idaho, Oregon, and Washington
(Ogbuji and Jensen I974). It has recently been ascertained that these populations
were probably M. chitwoodi (Santa, pers. communication). The histopathological
response of corn to infection by Meloigggyne incggnita are similar to other
plants in which multi-nucleate giant cells are formed. In some hybrids which cre
poor hosts, the giant cells collapse, resulting in the death of the nematode larvae
(Baldwin md Barker I970b).

5. Longidorus spp.
The needle nematode (Longidorus breviannulatus) was associated with

stunted field corn in Iowa (Norton and Hoffman I975). It has been found in

16

Illinois (Malek 9t_ 91. I980), Michigan (Rose, pers. communication), and other
Midwestern states. A number of other species, such as 9. elongatus, have been
found in Michigan corn fields (Bird, pers. comrmnication). _l__. breviannulatus at
high population densities may cause severe damage to field com. This nematode
usually has 01 extremely clumped field distribution, and obtaining damage
estimates for large areas is very difficult (Malek, pers. communication). It is a
very large nematode, and is usually found in soils which are composed of a

minimum of 90% sand (Malek a 59. I980).

6. Heterodera spp.
The corn cyst nematode (Heterodera zea) was found for the first time in,
the U.S. in Maryland (Puffinberger I98I). Heterodera zea is commme found
associated with corn in some regions of India, Egypt, and Pakistan. Host range is

limited to corn, barley, oats, and two other grasses (Puffinberger I98”.

7. Belonolaimus spp.
The sting nematode (Belonolaimus spp.) can be a severe problem on field
corn in the southern U.S. (Barker I978, Norton I978). This large nematode is

highly pathogenic md is confined primarily to sandy soils (Norton I978).

8. Other Nematodes

Field corn is a host of many other plant parasitic nematode species. The
host parasite relationships of nematodes such as Trichodorus spp.,
Macroposthonia spp., Helicotylenchus spp., lioploaimus spp., and Paratylenchus

spp., have not been investigated. These nematodes have been found associated

17

with corn in various parts of the U.S. (Chapman I954, Young I964, Baldwin md
Barker I970 a 8: b, Johnson and Chalfant I973, Barker I974, Johnson 9t_ 9_I. I974,
Johnson I975, Johnson 91 9_l. I975, Brodie I976, Norton I978, Norton _e_t_ 9l_. I978,
Smolik I978, Thomas I978, Norton I979).

A correlation of -0.5 was found between Helicotylenchus spp. soil
populations and corn yield (Norton g a_I. I978). Populations of M. pseudorobustus
did not significmtly decrease the mem dry root weight of corn in greenhouse
studies. It also had no influence on corn growth in combination with E.
hexincisus on Pioneer variety 3780 (Norton I979).

Based on the information available in I97 I, the Committee on Crop Losses
of the Society of Nematologists published estimates of crop losses due to plant
parasitic nemtodes in the United States. The reported estimates were based on
published research aid personal communications with nematologists md
agricultui'alists. According to these estimates, approximately 5% of the nation's
corn crop is lost annually to plant parasitic nematodes. This is equivalent to
203,l88,700 bushels or a national loss of $238,524,000 for the year l967-l968
(Committee for Crop Loss I97l). It is obvious that many plant parasitic
nematodes are associated with field corn production in the U.S., and that a
number of these nematodes cause significant economic losses of corn crop yield
(Committee for Crop Loss I97l). In many cases, corn roots may harbor high
population densities of nematodes and exhibit little root abnormality or
decreased growth. There appears to be some necessity for environmental stress

concomitant to infection for damage to be severe (Graham I954, Nelson I956).

18

C. Ecology of Plant Parasitic Nematodes
The understanding of nematode ecology is vital to effective nematode
management in agricultural ecosystems. Soil parameters and community ecology

interactions are among the most significant components of this important topic.

I. Soil parameters

Nematodes exhibit preferences for specific soil types in relation to
distribution, reproduction, and association with specific crop plants (Wallace
I973, Barker I978, Norton I978). Soils under cultivation usually harbor both
plant parasitic nematodes and saprozoic forms (Oostenbrink Q 91. I956).

A study of soil types md associated nematode genera in Manitoba showed
that clay soils harbored more nematodes than sandy soils. It was postulated that
differences in population densities of nematodes were correlated with
differences in nitrogen, potassium, and soluble salts in the soil solution, and not
with soil type (Kimpinski and Welch I97l). In British moorland soils, Banage ‘
(I963) has observed that the nematode taxa present and order of abundance of
different trophic groups may be constant and independent of the soil type md
geographic area. In contrast to these studies, it has been an accepted truism of
plant nematology that the most severe nematode problems are found in light
sandy-textured soils (Norton 9191. I97 I, Barker I978). The community structure
of plant parasitic nematodes has been malyzed in different soil types in Indiana
and Illinois soybean fields. These studies revealed that community structures
tend to be similar on dark-colored, highly productive soybean soils throughout
Indiana and Illinois. Lighter-colored soils have community structures which

differ from those of darker soils aid from each other (Ferris 91 a_l. I97 I).

19

The highest population densities of nematodes in a study on corn in Georgia
were found at a depth where the soil was composed of 78% sand, 6% silt, and
l6% clay (Brodie I976). Damaged corn grown on sandy soils in Iowa is commonly
associated with high plant parasitic nematode population densities (Norton and
Hinz I976). Population densities of E. hexincisus in Iowa are significantly higher
in Buckner coarse sand thm in other soil types (Zirakparzar g 91. I980). It was
reported that nematode movement is influenced by soil texture, and is a function
of the ratio of nematode size and pore and particle size (Wallace I973).
Maximum movement and migration of Pratylenchus spp. occur in sandy loam
soils compared with finer-textured soils (Endo I959, Townshend I972). Studies
with )1. americanum showed that soils with extremes in pore size, limited air-
filled pore space, or high organic matter content are deleterious to the migration
and survival of this nematode (Ponchillia I972). There is also a relation between
the soil texture and the soil temperature fluctuation. This relationship results in
differential requirements for heat unit accumulation for changes in physiological
development for _P_. hexincisus (Zirakparzar _t 9I_. I980).

Studies on the relationship between soil moisture and various nematode
activities indicated that 70-80% of field capacity provides optimal conditions for
the nematodes (Brodie I976). However, it should not be ignored that soil types,
particle size, and pore space influence soil aeration and also the soil moisture
potential. The moisture content of the soil, pore space, and aeration are all
interrelated (Norton I978).

Effects of soil disturbance through cultivation on plant parasitic nematodes
have received some attention. Conservation tillage regimes, or no-till regimes,

tend to allow nematode densities to increase above that of more conventional

20

tillage practices. A regular fall or spring plow offers suitable means of reducing
soil erosion without significantly increasing nematode numbers (Thomas I978).

This may be offset by concomitant increases in natural enemies.

2. Community ecology

A community cm be defined as m assemblage of ecologically related
organisms composed of two or more species in a prescribed area or habitat (Dice
I962, Krebs I978). Some ecologists stress the relationships among species, while
others place emphasis on the assemblage of species which is typically found in
the same habitat (Andrewartha md Birch I954). A community may be of varied
size, and depends upon the identified reference point. The area chosen for study
is usually one that the ecologist regards as a convenient entity for consideration.
It is usually somewhat homogeneous. The term homogeneous, however, is rather
nebust in ecological terms (Pielou I977).

There are mmy difficulties in dealing with communities of orgcnisms, and
obtaining an understmding of their organization. It has been noted that "the
task of unraveling the ecological relationships in even a simple community has
usually proved impracticable" (Andrewartha and Birch I954). Community
interrelationships are complex, and the distribution and abundance of the
component species cannot be explained by the simple interrelations among
orgmisms, and must include a myriad of environmental factors (Dice I954,
Andrewartha and Birch I954, Pielou I974).

Ecologists would like to understand the degree of species interdependence
within communities, how distributions within communities reflect environmental

factors, and the role of communities within ecosystem activities such as nutrient

21

cycling, energy transfer md succession (Barbour et aI. I980). Communities must
be measured and summarized before such progress can be accommodated.
According to Krebs (I978) there are five traditional characteristics of
communities which are of primary interest: species diversity, growth form and
structure, dominance, relative abundance, and trophic structure. Organisms may
be found in areas to which they are suited. Thus, the concepts of commonness
and rarity reflect m organism's suitability for the area. The fact that orgmisms
can frequently be shown to have distinct boundaries reflects this fact. The
question of why at organism is found in a particular area is difficult to mproach.
Frequently an organism may not be found in areas that appear to be perfectly
acceptable as habitats. The obvious factors influencing the distribution of an
organism such as moisture and temperature are often not adequate to explain an
organism's distribution.

Species usually occur in discontinuous patterns or patches, between which
the species is often rare or absent (Cole I949, Andrewartha I96l, Dice I962).
Species which have ecologic relations with one another tend to occur together
md communities are formed (Dice I962). The character and current site of
many natural ecosystems have been greatly influenced by humankind, perhaps
none more than agroecosystem. These man-made communities are obviously of
great importance to the welfare of humankind. A number of methods have been
developed to quantitatively attain an improved understanding of community
structure. Some of these methods are community ordination, canonical variate
analysis, diversity indices, and measures of association. Each approach to
understmding the community suffers from certain limitations.

Polar ordination is a procedure used to summarize sampling data.

22

Ordination is simply the plotting of species or sample data on coordinate axes.
The axes may represent environmental factors or mathematical constructs
derived from matrices of similarity or community coefficients (Poole I974,
Barbour e_t 9l_. I980). The ordination results in the data points being dispersed in
an n-dimensional space, with each of the dimensions representing a coordinate
related to a specific parameter. The distance between points is an indication of
the degree of similarity or difference between points, thereby showing a pattern
of continuous relationships which can be interpreted in terms of the
environment, or other factors (Bray md Curtis I957). One problem with this
method is that the reference points of each axis are chosen by the investigator
md the resulting ordination does not necessarily explain why the relationships
exist. Relating the axis to the environment is also a problem (Barbour 91 91.
I980). An alternative method of ordination, principal component ordination, has
similar difficulties in that the axes often have little biological interpretability
(Poole I974). Principal components and polar ordination have an additional
weakness. Each component of the analysis is assumed to be a linear function of
the species. The species in a set of quadrats on (11 environmental gradient are
not linearly related. Thus the position of the quadrats in the ordination may not
reflect the true relationship between quadrats (Poole I974).

Cmonical variate analysis is similar to ordination, but in addition to
species abundmce information, qumtitative measures of environmental factors
may be included. This type of analysis permits inquiry into the interrelationships
between two sets of data. The canonical variates obtained from the analysis

provide between-set correlations for the environmental md species data (Pielou

I 977).

23

Diversity indices provide a representation of community variability that
can be compared to other community properties such as productivity, stability or
environmental conditions. The proportion of species present in the studied area
is important in this regard. Several indices have been proposed. One of the more
useful indices is the Shaman-Weaver index (Pielou I977). Much of the work in
community ecology has been directed at measuring associations between species
(Cole I949, Dice I954). The basic goal of these types of analysis is the
formalization or quantification of the basic idea of community organization.
Several methods of measuring associations between species have been proposed
(Cole I949). Cole's measurement of interspecific association detects
interrelationships among species (Cole I949). According to this measure, if two
species occurred together as many times as they possibly could have, the
association is perfect, or l.0. If they occurred together the minimal possible
number of times, the association is perfectly negative, -I.0. If the number of
joint occurrences is exactly what is expected on the hypothesis of independent
scattering of the two species, no association is indicated and the association
value is 0.0 (Cole I949). One defect of this measure is that no distinction is
made between complete (when A is never found without B, though B may be
found without A) and absolute (when neither species ever occurs without the
other) asociation (Pielou I977). This problem is not critical, and does not
significantly diminish the usefulness of the measure.

All existing community ecology analysis procedures present problems of
intrepretation in that the association malysis of quadrat data depend on the size
of the quadrat used and the distribution of the organisms studied (Pielou I977,

Krebs I978). An additional problem is related to the biological interpretation

24

of measures of association. The fact that a positive association is found between
two species does not mean that one is necessary or beneficial to the presence of
the other species (Cole I949, Pielou I974). Further, since it is impossible to
census 0 community, the association observed between members may in fact
represent a shared relationship to an unobserved factor.

Several studies on nematode community ecology are available. Ferris 91
a_l. (I97l) used community ordination techniques to study the community
structure of plant parasitic nematodes in relation to soil type in soybean fields.
It was found that lighter-colored soils had community structures which differed
from those of darker-colored soils. Johnson 91 91. (I972, I973) used resemblance
equations md community ordination techniques to malyze nematode community
structure in forest woodlots. These studies showed that woodlots containing
similar nematode species also exhibited similarities in dominmt tree species aid
soil types. They concluded that it seemed unlikely that any one factor would

have a dominating influence over the whole community.

D. Nematode Population Management

The management of plmt parasitic nematodes in field corn production
systems has become an issue of importmce in recent years (Norton I978). The
availability of economical non-fumigant chemical control measures contributed
to this interest. Prior to an overview of chemical control methods, however, it
is of interest to evaluate some of the factors which play a role in the
determination of nematode population growth associated with field corn. Many
of these factors play a significant role in production system management

strategies.

25

Soil amendments, soil micro-organisms, tillage regime, and soil type
influence nematode populations commonly associated with agricultural
ecosystems (Endo I959, Walker I969, Walker l97l, Thomas I978). The influence
of micro-organisms on populations of Pratylenchus spp., and their pathogenicity
has been studied. Microbial fauna and their degradation products are frequently
responsible for the decline of nematode populations after incorporation of
bacterial- and microbial-containing orgmic amendments. Some of the influence
exerted by these fauna may be the result of metabolic breakdown products,
including simple nitrogeneous compounds (Walker I969).

Populations of Pratylenchus penetrans decrease in soil following the
addition of nitrogen amendments in the form of nitrate, nitrite, orgmic nitrogen,
or ammonium compounds. Population reduction observed in these instances was
attributed to ammonification during decomposition, and this hypothesis is
supported by malysis of soil atmospheres. Again, it is believed that
decomposition of nitrogeneous substmces by the soil microbial fauna is the
principal reason for the decline in soil populations of the nematodes. The direct
or indirect effect of pH, Ca+ ions, moisture, temperature, and other factors will
affect microbial activity md nitrification, and thus nematode populations
(Walker l969& I97l).

Tillage regimes affect populations of other plant parasitic nematodes
associated with field corn. Helicotylenchus spp., Pratylenchus spp., md
Xi9henema spp. occur in higher densities under no-till, or minimum tillage
regimes. The lowest numbers of these same genera were found to occur in fields
utilizing spring md fall plowing. Possible causes for these reductions in

populations are delay in egg hatch due to differential soil warming, surface

26

accumulation of debris acting as a mulch affecting moisture retention, warming
rate, and depth of root growth. The accumulation of debris may also increase
the spread of fungal populations which impact on the nematode populations
(Thomas I978).

Crop rotations are among the oldest md most important approaches to
controlling plant parasitic nematodes associated with agricultural crops. The
value of rotation is well known and has been implemented as the principle
control strategy outside of the use of chemical control measures (Nusbaum and
Ferris I973). A problem associated with rotations as a control strategy is that
common rotation crops are frequently susceptible to a number of different
nematode species, and that the nematodes present in a community represent a
broad spectrum of genetic diversity. Implementation of a rotation strategy
which controls one nematode species may allow other members of the
community to reach damaging levels. It has been noted that agroecosystems
which have been under cultivation for mmy years tend to harbor more plmt
parasitic species than monocultures of short duration. Correlation usually exists
between the cropping sequence did the composition and damage caused by the
nematode community (Oostenbrink 91 a_l. I956). Specific rotations have been
observed to either decrease or increase the population levels of the nematode
community (Oostenbrink 91 91. I956). A number of cropping rotation systems
have been studied, and it has been noted that high population densities of
Pratylenchus spp. are associated with most common field crop rotation
sequences, of which corn is a component (Oostenbrink 91 a_l. I956, Ferris and
Bernard l97l, Barker I978).

In recent years much advancement in the field of breeding crops for

27

resistance to disease has been realized (Roane I973). Various sweet corn
cultivars have differential resistance to plant parasitic nematodes (Johnson
I975). Studies have shown that although inbred lines of field corn possess
resistmce to nematode populations, single crosses from these inbred lines do not
possess the resistance. Thus, in some cases, nematode resistance may be due to
recessive genes (Nelson I956). Known nematode-resistant field corn cultivars
are not currently available on a commercial basis in the U.S. (Barker I978).
Although crop rotation is one of several possible approaches to nematode
control, its popularity decreased in some regions as corn production intensified,
and advances in agricultural technology resulted in the development of
economical chemical controls. There are relatively few reports of chemical
control methods effective for controlling nematodes associated with field corn
(Young I964, Johnson md Chalfant I973, Norton and Hinz I976, Norton fl a_l.
I976). Early work with fumigant materials indicated that‘fumigants effectively
control nematodes such as Trichodorus spp., Pratylenchus spp., Xiphenema spp.,
Criconemoides spp. and Belonolaimus longicaudatus, md result in significantly
increased yields in the southern U.S. (Young I964, Johnson and Chalfant I973).
Most non-fumigant pesticides used to control nematodes in corn production
also possess insecticidal properties. It is thus important to note that the
increased plant growth md yield may be due to several factors other than to the
control of nematodes (Johnson md Chalfant I973, Norton et al. I978).
Significant negative correlations of nematodes with corn yield are not proof that
the control of nematodes is responsible for a yield increase. Such correlations
however, frequently support the hypothesis that nematodes do cause

economically significant damage to field corn (Norton 9191. I978).

28

In field experiments in Ontario, carbofuran was found to significantly
increase the grain yield of corn. The increased yield, however, could not be
attributed to control of insects. It was suggested that nematodes were a possible
cause for the resultant increase in yield (Daynard 91 91. I975). Since that study,
carbofuran has been cited as significmtly controlling plant parasitic nematodes
associated with field corn (Norton I978, Norton and Hinz I976). There is no
evidence that carbofuran functions as a growth regulator, resulting in increased
shoot and root growth of corn (Rogers and Owen I974, Norton and Hinz I976).
Apparent nematode resistmce to carbofuran was observed (Smolik I978). It was
suggested that populations of Pratylenchus scribneri may become tolerant to
carbofuran following extended exposure to sub-lethal insecticidal dosages of the
chemical. Subsequent carbofuran use at nematicidal rates failed to significantly
increase corn yields. There has been no further corroboration of these
observations.

Two papers indicate that aldicarb is 01 effective nematicide in production
of sweet and field corn (Johnson and Chalfant I973, Norton 91 a_l. I978). The
effectiveness of aldicarb in promoting a yield increase may be
considered a reliable indicator that nematodes are responsible for the decreased
growth, since aldicarb is not effective in controlling corn rootworm (Norton _e_t
a_l. I978). Other chemicals which may be used to control plant parasitic
nematodes on field corn include: ethoprop, phenamiphos, carbofuran md
terbufos (Hart I976).

Improved crop loss assessment procedures and nematode control measures
in field corn production, as well as a better understanding of environmental

interactions, are essential for future field corn production (Norton I978).

29

The economics of nematode control on field corn, however, has not been
discussed in the current literature. It is important to consider that yield
increases of I0-l4% associated with nematode control may represent a
somewhat minor return on the control investment, considering the importance of
environmental fluctuations in determining the severity of damage caused by a

given population level of a particular nematode (Barker I978, Norton I978).

Ill. MATERIALS AND METHODS
A. Michigm Field Corn Survey

A survey of Michigan field corn production was conducted during the
summer of I979. It was used to determine what plant parasitic nematodes are
associated with Michigm corn production, and the geographic distribution of
these nematodes.

The I978 Michigm Agricultural Reporting Service Statistics were used for
the design of the survey. Data on total corn acres planted md harvested for
grain and silage on a per county basis were used to group the counties into six
geographical regions (Fig. 3). Thirty-eight counties were chosen from the
geographical regions on the basis of the production per county within each region
(Fig. 4). Each region was represented by at least five counties.

Each of the surveyed counties was sampled in four different locations.
Sample sites consisted of a minimum of 40 acres of corn. Each site was sub-
sampled four times. the sub-samples each represented l0 acres, and consisted of
composite samples of root material from four plants and soil from a large area
within the IO-acre sub-sampling zone.

The Michigm State University Cooperative Extension Service Agricultural

30

Figure 3. Counties sampled during the I979 Michigan field corn
survey, grouped into 6 geographic regions.

 

31

 

 

 

 

 

32

Figure 4. Counties sampled during the I979 Survey.

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Presque Isle
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33)
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Newaygo
Muskegon
Montcalm
Gratiot
Saginaw
Kent
Clinton
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Barry
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Washington
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Extension Agent, County Extension Director, or Field Crops Agent in each of the
selected counties was contacted and requested to identify four appropriate field
corn production system sites for the survey. The sample site selection criteria
were as follows:

I. Identify sites not suspected to have nematode or disease
problems.

2. Forty acres of field corn must be available for sampling.

3. The locations of the four sample sites should reflect the
distribution of field corn production within the county.

4. Production system inputs such as soil type, rotation, fertilizer,
cultivar, tillage, and insecticide application must be available for
the survey.

The survey was begun on July l9, I979, and completed on October 2, I979.
This represented a range of cumulative degree days of 9l5 to 2660 at a base of
IO°C (Figure 5). At each site, soil and root samples were taken using a foot tube
sampler and trowel (Bird and Elliott I980). Samples were taken from a depth of
4 to 24 cm in the root zone of each plant sampled. Sample sites of 40 acres were
located and their geometry assessed. An approach to sampling was utilized
which would allow the field to be divided into 4 approximately equal IO-acre
sections. Each IO-acre section was sampled as described by Barker (I978).
Roots from at least four corn plants, and soil cores from c_a. 20 plants were
taken as the sub-samples of each lO-acre sample. Soil and root sub-samples
from each IO-acre section were thoroughly mixed in polyethylene bags md
retained as separate samples for nematode analysis. The soil type from which

each sub-sample was taken was estimated by visual inspection. Samples were

35

Figure 5. Cumulative degree days (base lO°C) as calculated from
April I, I980, to the sampling date specific for each
county included in the Michigan field corn survey.

36

 

 

 

 

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37

packaged in polyethylene bags and returned to Michigan State University. The
samples were stored at 4 to l0°C until processing.

For quantitative md qualitative estimation of nematode populations, roots
were removed from the soil sample and rinsed to remove adhering soil particles.
Two grams of root material from each sample were selected at random and
processed using the gyratory shaker method (Bird I97 I). The procedure used for
the study is outlined in detail in Appendix A. The liquid nematode-containing
suspension was decanted through IOO over 400 mesh screen series. The contents
of the 400 mesh screen was rinsed into test tubes for counting. A l00 cm3 sub-
sample of each soil sample was processed for nematodes using the centrifugation
sugar flotation method (Caveness md Jensen I955). The procedure is described
in detail in Appendix B. Nematode suspensions not analyzed immediately were
stored at 4 to l0°C until microscopic observation and quantitative population
estimation was accomplished. Prior to observation the volume of water in each
sample test tube was reduced to approximately I to 2 ml by aspiration. The
remaining volume of water was agitated, and rinsed with l.5 ml of distilled water
onto a S x 5 cm glass counting dish. One quarter of the counting dish was
censused using a compound microscope at ISO x. The plant parasitic nematodes
present were identified to genus, and the number of each genus present was
noted. All estimates of nematode populations in root and soil for the work
contained in this thesis were obtained using these techniques unless otherwise
noted. After soil md root processing, nematode identification and population
density estimation, the data for each of the six geographic regions were
summarized using six community ecology analysis procedures.

Absolute frequencies and relative frequencies, absolute density, relative

38

densities, prominence values, and Cole's measure of interspecific association
were calculated as follows:
Eq. I. Absolute frequency = ("i/nt) x IOO = AF
Eq. 2. Relative frequency = (fi/ 2 fi) x IOO = RF
where n; = number of samples containing a genus
nt = number of samples collected
fi = absolute frequency of genus
22fi = "sum of absolute frequency of all genera
Eq. 3. Absolute density = absolute numbers per unit sample = AD
Eq. 4 Relative density = (ti/ 2 ti) x IOO = RD
where ti = number of individuals of a genus in a region
).‘.ti = total of all individuals in a region
Eq. 5. Prominence value = AD x/KF = PV
Eq. 6. Contingency table analyses of associations among genera in
each region were performed using Cole's measure of interspecific
association (Cole I949). The equations for this procedure are
presented in detail in Appendix C. Significant values of
association were tested using an uncorrected Chi-square test of
independence.
The soil from 72 samples was subjected to mechanical soil textural analysis
(Appendix F). The resulting data were used to plot high and low population
densities of Pratylenchus spp. and Tylenchorhynchus spp. versus soil type on soil

textural triangles. High population densities of Helicotylenchus spp. and

Paratylenchus spp. were plotted in a similar fashion.

39

B. Nematode Control Evaluations

During the summer of I980, three field trials were used to determine the
effect of selected nematicides on nematode population dynamics and grain yield.
Each test location was selected on the basis of results of the I979 state-wide
field corn survey, md had relatively high population densities of Pratylenchus

penetrans. A summary of the pesticides applied is presented in Appendix E.

l. Hal Benn corn production site

The first nematode test included as part of the thesis was located in
Jackson County, on the farm of Hal Benn. The soil type was a sandy loam (69%
smd, l596 silt, l6% clay). Five pesticide treatments and a non-treated control
were used in a rmdomized complete block (Table l). Each treatment was
replicated five times. Each replication consisted of four rows of corn l5.2
meters in length, with the rows 96.5 cm apart. The methyl bromide treatment
was applied md tarped on May l6. The tarp was removed on May l8. All pre-
plant nematode samples were taken prior to soil fumigation. Pre-plant soil
samples were obtained using a foot tube sampler. Composite cores consisted of
soil from the outer two rows of each treatment replication. Root samples were
obtained using a trowel, and were removed from two plants in each of the outer
two rows of each treatment replication. Soil adhering to the root mass was
included in the sample. Roots md soil were mixed thoroughly in plastic bags.
Subsequent processing md analysis of root and soil samples were performed as
outlined in the materials md methods section of the statewide corn survey. The
other pesticide treatments were applied at planting on May 2, I980. The

experimental area was planted with cultivar F unks G-4256 hybrid corn.

40

Table 1. Pesticides applied at Hal Benn corn production site in Jackson

 

 

County.
Application
Treatment rate Application method
Methyl Bromide 392 kg/ha Broadcast (injected and tarped)
Phenamiphos 112 kg/ha Broadcast
PCNB and Thiazole 13.4 kg . active ingredient (ai)ha 7" band
Carbofuran (low) 0.56 kg ai/ha 7" band

Carbofuran (high) 2.24 kg ai/ha 7" band

 

41

The Hal Benn corn production site was sampled eight times over the course
of the season. The first samples were taken prior to fumigation, and
subsequently at 299, 750, l54l, l9l8, 2609, and 2662 degree days (base lO°C).
The degree-day accumulation for each sampling date was obtained from the
Michigm State University Pest Management Executive System (PMEX) weather
data base in Jackson County. Soil and root samples were taken from the outer
two rows in each treatment. Samples were comprised of soil and roots from two
plants for each row sampled. Sampling depth was 4 to 24 centimeters. Samples
were processed in the manner previously described for the corn survey.
Nematode population density estimates were assessed under the binocular
microscope at 40-80X. The heights of three plants per treatment were measured
at the first two post-plmt sampling dates.

Yield estimates were obtained by hand harvesting the inner two rows in
each treatment replication on October l6, I980. Shelled grain was weighed, and

the percent moisture determined.

2. Floyd Baum corn production site

The second nematicide evaluation location was in Jackson County, on the
farm of Floyd Baum. The soil type was a loam. Mechmical soil analysis was not
performed at this site. Eight non-fumigant nematicide-insecticide treatments
md a non-treated control were evaluated using a randomized complete block
design with five replications of each treatment (Table 2). Each treatment
consisted of four rows 9.l m in length and 76.2 cm apart. Funks 6-4256 was
planted, and treatments applied on May 6. Pre-plant samples were taken prior to

treatment. Soil and root samples were obtained md analyzed using the same

42

Table 2. Pesticides applied at Floyd Baum corn production
site in Jackson County.

 

 

Treatment Application rate Application
method

Terbufos (low) 3.7 kg/ai/Ha 7 inch band
Terbufos (high) 7.4 kg/ai/Ha 7 inch band
Ethoprop (low) 1.1 kg/ai/Ha 7 inch band
Ethoprop (med) 1.7 kg/ai/Ha 7 inch band
Ethoprop (high) 2.2 kg/ai/Ha 7 inch band
Aldicarb (low) 1.1 kg/ai/Ha 7 inch band
Aldicarb (high) 1.7 kg/ai/Ha 7 inch band
Carbofuran 2.2 kg/ai/Ha 7 inch band

 

43

techniques used at the Hal Benn site. The Floyd Baum corn production site was
sampled four times over the course of the season. The first samples were taken
prior to planting, and subsequently at 35l, ”40, and 2670 degree days (base
IO°C).

The plot was harvested on October 7, I980. Yield estimates were obtained
by hand harvesting the inner two rows of each experimental unit. The shelled
grain was weighed md the percent moisture was measured.

3. Alan Cable corn production site

The third nematicide evaluation location was in Clinton County on the
farm of Alan Cable. The soil type was a clay loam (4l96 sand, 25% silt, 34%
clay). Eleven nematicide-insecticide treatments md a non-treated control were
evaluated using a randomized complete block design, with five replications
(Table 3). Each treatment consisted of four rows l5.2 m in length md lOl cm
apart. Pioneer 3780 was planted, and treatments applied on May l6, I980. Pre-
plant samples were taken prior to treatment. Soil and root samples were
obtained and analyzed using the same techniques used at the Hal Benn site. The
Alan Cable corn production site was sampled four times over the course of the
season. The first samples were taken prior to planting, and subsequently at 3l5,
I778, and 2295 degree days (base |0°C).

The plot was harvested on November l2, I980. Yield estimates were
obtained by hand harvesting the inner two rows of each experimental unit. The

shelled grain was weighed Cl'ld the percent moisture was measured.

44

Table 3. Pesticides applied at the Alan Cable corn production site
in Clinton county.

 

 

Treatment Application rate Application method
Fonofos 1.1 kg ai/ha 7 inch band
Chlorpyrifos 3.7 kg ai/ha 7 inch band
Terbufor 3.7 kg ai/ha 7 inch band
Terbufos 7.4 kg ai/ha 7 inch band
EthOprOp 1.1 kg ai/ha 7 inch band
Ethoprop 1.7 kg ai/ha 7 inch band
EthOprOp 2.2-kg ai/ha 7 inch band
Aldicarb 1.1 kg ai/ha 7 inch band
Aldicarb 1.7 kg ai/ha 7 inch band
Carbofuran 0.56 kg ai/ha 7 inch band
Carbofuran 2.2 kg ai/ha 7 inch band

 

45

IV. RESULTS

A. Michigan Field Corn Survey

Seven genera of plant parasitic nematodes were detected during the survey
(Pratylenchus spp., Tylenchorhynchus spp., Paratylenchus spp., Tylenchus spp.,
Criconemoides spp., Helicotylenchus spp. and Heterodera spp.). Pratylenchus
spp. were recovered most frequently, being found in 98% of the samples taken
(Table 4). The mem population density of Pratylenchus spp. was 62.3 per l.0
gram of fresh weight of root tissue, with a range of O to l096. The mean
population density of Pratylenchus spp. was l0.5 per IOO cm3 soil, with a range
of 0 to l88.

 

Tylenchorhynchus spp. was the second most frequent plant parasitic
nematode detected. It was found in 3l% of the samples collected (Table 4). The
mean population density was 5.8 per IOO cm3 soil, with a range of 0 to 464.

The five additional plant parasitic genera were recovered less frequently.
Paratylenchus spp. were found in 24% of the samples, Tylenchus spp. in 23%,
Criconemoides spp. in l3%, Helicotjlenchus spp. in 8%, and Heterodera spp. in
|%. Predatory nematodes, primarily Mylonchulus spp., were recovered from l7%
of the samples.

Pratylenchus spp. were the dominmt plant parasitic nematodes observed
associated with Michigm field corn. In all but three of the sampled counties,
Pratylenchus spp. had the highest absolute frequency, relative density, and
prominence value. Paratylenchus spp., Helicotylenchus spp., and
Tylenchorhynchus spp. were the other plant parasites observed with some
regularity. ln Lenawee County, Helicotylenchus spp. had the highest relative

density md prominence value. In Monroe County, Helicotylenchus spp. and

46

Table ll Prat lenchus spp. and Tylenchorhynchus spp. populations recovered
from 152 field corn production sites in Michigan.

 

 

 

Pratylenchus spp. Tylenchorhynchus spp.
County sites No. per 100cm3 No. per 1.0 9 sites No. per 100
infested (range) root (range) infested cm3 (range)

Allegan 100 3.8 (4-24) 18.0 (0-116) 50 15.0 (12-68)
Alpena 100 2.5 (4-16) 29.1 (4-84) 25 3.5 (0-56)
Antrim 100 13.2 (4-28 24.1 (0-130) 20 3.0 (0-48)
Arenac 100 10.3 (0-40) 48.1 (0-428) 50 4.0 (0-32)
Bay 75 2.3 (0-12) 55.1 (0-426) 25 0.0 (0-0)
Berrien 100 4.8 (0-24) 5.0 (0-28) 0 0.0 (0-0)
Barry 100 1.5 (0-8) 60.5 (0-466) 50 1.3 (0-8)
Branch 100 25.8 (4-80) 498.8 (28-1096) 50 7.0 (0-104)
Charlevoix 100 75.5 (0-64) 24.8 (0-52) 33 1.8 (0-32)
Clinton 100 7.5 (0-36) 90.1 (4-556) 100 16.3 (0-168)
Delta. 80 20.8 (0-32) 82.0 (0-644) 20 1.3 (0-8)
Dickinson 100 18.3 (0-92). 62.9 (0-298) 0 0.0 (0-0)
Grand _ ' '

Traverse 100 50.5 (4-188) 42.5 (0-218) 40 1.8 (0-24)
Gratlot 100 13.3 (0-36) 37.5 (0-296) 50 14.8 (0-96)
Hillsdale 100 8.0 (0-28) 27.5 (0-82) 33 3.8 (0-32)
Houghton 100 7.5 (0-36) 57.5 (2-120) 0 0.0 (0-0)
Huron 100 2.8 (0-12) 10.3 (0-44) 0 0.0 (0-0)
10560 100 4.5 (0-28) 39.0 (1-206) 0 0.0 (0-0)
Jackson 100 13.8 (0-44) 295.0 (0-832) 20 1.8 (0-28)
Kent 100 4.3 (0-20) 9.5 (0-104) 0 0.0 (0-0)

Lapeer 100 16.3 (0-44) 22.2 (8-70) 50 10.3 (0-64)

47
Table 4 (continued).

 

Leelanau 100 25.8 (0-48) 75.7 (4-342) 14 1.0 (0-15
Lenawee 100 0.5 (0-4) 5.1 (0-52) 25 0.5 (0-8)
Mackinac 100 9.5 (0-32) 121.0 (0-518) 25 0.3 (0-4)
Menominee 100 14.8 (0-48) 82.8 (4-114) 25 0.5 (0-8)
Missaukee 100 15.0 (4-48) 59.1 (8-110) 25 0.3 (0-4)
Monroe 75 0.5 (0-4) 3.5 (0-15) 100 9.0 (0-52)
Montcalm 100 19.0 (0-54) 109.0 (1-908) 0 0.0 (0-0)
Muskegon 100 14.3 (0-88) 40.4 (0-332) 55 82.5 (0-454)
Newaygo 100 5.0 (0-20) 37.5 (0-255) 14 1.5 (0-12)
Ogemaw 100 2.5 (0-8) 52.4 (0-140) 50 1.5 (0-12)
Presque Isle 100 12.5 (0-124) 48.3 (0-192) 0 0.0 (0-0)
Saginaw 100 7.3 (0-24) 21.5 (0-108) 50 21.5 (0-140)
Sanilac 100 4.8 (0-15) 9.5 (0-50) 50 3.5 (0-28)
St. Joseph 100 -missing- 27.1 (0-250) 0 0.0 (0-0)
Tuscola 100 3.0 (0-12) 9.8 (0-50) 50 1.5 (0-20
' wasntenaw 100 2.4 (0-12) 52.0 (0-222) 40 5.0 (0-8)
Michigan 98 i = 10.5 i = 52.3 31 i = 5.8
U a = 9.9 o = 89.4 a = 14.0

 

48

Tylenchorhynchus spp. had absolute frequencies, relative densities and
prominence values higher than Pratylenchus spp. In Saginaw County,
Helicotylenchus spp. had the highest absolute frequency, relative density, and
prominence value. The relative frequencies and prominence values for the
nematode genera were similar for each geographic region (Tables 5 did 6).

Coefficients of association between nematodes within regions yielded no
recurrent specific associations between taxa at the regional level. Coefficients
which differed from zero with respect to the standard error were tested using a
chi-square test of independence. Using the chi-square test, the null hypothesis
was rejected when (p _<_ 0.l l) (Tables 7 and 8).

Several associations were significant according to these criteria. These
significant associations were not observed with any regularity across the
geographic regions of the survey; associations between specific taxa usually
occurred in only one or two counties. When the associations within regions were
compared to the associations obtained for the state as a whole, several of the
combinations of taxa were significant for both analyses. Tylenchorhynchus spp.
and Helicotylenchus spp., Tylenchorhynchus spp. and Paratylenchus spp.,
Paratylenchus spp. and Criconemoides spp., and Tylenchus spp. and
Helicotjlenchus spp. all had slightly positive associations in at least one rgion of
the state, end for the state as a whole (Tables 7 and 9). Several combinations of
taxa which had significant associations on a regional level did not have such
associations an the state level.

Associations of predatory nematodes with plant parasitic taxa varied; some
were negatively associated and some were positively associated on a regional

level (Table 8). There were no significant associations between predatory

49

 

 

 

 

 

 

 

 

 

 

 

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50

 

 

 

 

 

 

 

 

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51

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52

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53

 

 

 

 

 

 

 

 

 

 

 

 

 

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54

nematodes and plant parasitic taxa when the analysis was conducted for the
state.

The predominmt soil type encountered was loam, comprising 4l% of the
sample sites. Smdy loam was observed at 25% of the sites, clay loam at l5%,
smd at l2%, clay at 4%, and organic soil at 3%. Poor growth of corn with
respect to surrounding corn was found at 8% of the sample sites. Poor growth
was not associated with especially high nematode densities with respect to the
surrounding corn growth. Population densities were termed low when the density

3

of a given taxa per gram root plus l00 cm of soil was 0 to l0. Densities were

termed high for all genera except Pratylenchus, when this sum was greater than

 

20. Pratylenchus spp. population densities were termed high when this sum was
greater thm l00. Comparison of population densities of Pratylenchus spp.,
Tylenchorhynchus spp., Helicotylenchus spp., and Paratylenchus spp. with soil
type yielded no relation between population density md soil type (Figures 6-l I).
High md low densities of Pratylenchus spp., and Tylenchorhynchus spp. were
found in a variety of sandy soils. High densities of Pratylenchus spp. and
Helicotylenchus spp. were also found in a variety of smdy soils.

None of the survey sites received nematicidal rates of pesticides applied at
planting, and 53% of the survey sites received no pre-plant pesticide treatment.
Carbofuran was applied at insecticidal rates at 20% of the sample sites, fonofos

at l3%, terbufos at 4%, ethoprop at l%, and other insecticides at 9%.

B. Nematode Population Mmagement Trials
l. Hal Benn corn production site
There were no significant (P = 0.05) pre-plant differences in soil population

densities of Pratylenchus penetrans among the areas used for the experimental

55

Figure 6. Soil types for low population densities of Pratylenchus
spp. as recovered during the I979 field corn survey plotted
on a soil textural triangle.

Figure 7. Soil types for high population densities of Pratylenchus
spp. as recovered during the I979 field corn survey
plotted on a soil textural triangle.

56

Ill)! Cl."

 

 

         
    

   
  
   

  
  

.[
an 70 50 50 ‘0 30 20 15 111025111
100mm
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SILT LOAN

Ill)! SIU

Figure 6.

Figure 7.

55

Soil types for low population densities of Pratylenchus
spp. as recovered during the I979 field corn survey plotted
on a soil textural triangle.

Soil types for high population densities of Pratylenchus
spp. as recovered during the I979 field corn survey
plotted on a soil textural triangle.

56

Ill)! (1M

 

 

anrnsosomwz'oiémozslu

      
 

I, SIlIV
CLAY

 

10015111090 80 70 60 50 *0 30 2016111015111

57

Figure 8. Soil types for low population densities of
Tylenchorhynchus spp. as recovered during the I979 field
corn survey plotted on a soil textural triangle.

Figure 9. Soil types for high population densities of
Tylenchormrnchus spp. as recovered during the I979 field
corn survey plotted on a soil textural trimgle.

 

58

Ill)! CLAY

      
   
 

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i

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so 70 60 50 '10 30 20 10 10015111

59

Figure l0. Soil types for high population densities of Helicotylenchus
spp. as recovered during the I979 field corn survey
plotted on a soil textural triangle.

Figure ll. Soil types for high population densities of Paratylenchus
spp. as recovered during the I979 field corn survey plotted
on a soil textural trimgle.

60

 

 

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61

treatments at the Hal Benn site (Table ID). The pesticides evaluated in this test
significantly altered the nematode population densities recovered from soil and
corn roots throughout the growing season. At 299 degree days the root and soil
population densities associated with the PCNB + thiazole treatment were
significmtly higher than those associated with the other treatments (Tables l0
and l l). Plant heights were measured, did there was no significant difference in
plant heights among treatments (Table l2).

The next sampling period was at 750 degree days. Again, the PCNB +
thiazole (Dd control had significantly higher root population densities than the
other treatments, with the exception of the low level of carbofuran (Table II).
The soil populations at 750 degree days did not follow the same'trend as the root
populations with respect to treatment effects. Soil population densities in the
methyl bromide and phenamiphos treatments were significantly lower than all
other treatments. The control had higher soil populations than all treatments
except the PCNB + thiazole (Table l0). Plant heights were measured and the
methyl bro-mide treated plants were significantly taller than the plants in the
remaining treatments (Table l2).

At lS4l degree days, the root population densities in the PCNB + thiazole
were significantly higher than all treatments except the check (Table II). Soil
population densities in the PCNB + thiazole md control were also significantly
higher thm all other treatments (Table l0).

At l9l8 degree days the root population densities in the PCNB + thiazole
and check were still significantly higher than all other treatments. The methyl
bromide was not significantly different than the phenamiphos or either level of

carbofuran (Table ll). The low level of carbofuran had a significantly higher

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62

 

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63

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64

Table 12. Influence of_five. esticides on corn height at the Hal Benn
corn production 51 e.

 

Plant height (cm)

 

Treatment 299dd1 750dd
Methyl Bromide 56.4a2 80.8b
Phenamiphos 58.28 70.18
PCNB & Thiazole 53.6a 67.6a
Carbofuran (low) 54.6a 73.7ab
Carbofuran (high) 55.4a 73.9ab
Control 55.9a‘ 58.5a

 

1 Accummulative degree days (Base 10 c).

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

65

population density than the high level of carbofuran, or phenamiphos. The soil
population densities of the PCNB + thiazole and control were significantly higher
than all other treatments (Table l0). At 2609 degree days the treatment effects
on population densities could be divided into two groups for both root md soil.
PCNB + thiazole, low level of carbofuran, and the control had significantly
higher population densities in both root and soil than the remaining treatments.
Plots were harvested at 2662 degree days. The root population densities of
the PCNB + thiazole and the control were significantly higher than the other
treatments (Table l I). Only the PCNB + thiazole had a significantly higher soil
population density at harvest (Table ID). No significant differences in shelled
grain yield or percent moisture were found among treatments. Corn rootworm
(Diabrotica virgifera) adults were observed at the Benn site during the season.
The numbers were low, and populations of adults were not localized within

treatments.

2. Floyd Baum corn production site

Pre-plant samples at the Baum site yielded no significant differences in
soil population densities of Pratylenchus penetrans among treatments. The first
post-plant sampling period was at 35l degree days. The root population densities
of the control, low level of terbufos, and low level of ethoprop were significantly
higher than either rate of aldicarb or carbofuran. The medium and high levels of
ethoprop had root population densities significantly higher than the high rate of
aldicarb and carbofuran. There were no significant differences in soil population
densities among treatments (Table I3). At l I40 degree days the control and low

level of ethoprop had significantly higher root population densities than the high

66

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67

level of aldicarb and the carbofuran treatments. These four treatments were not
significantly different compared to the remaining treatments. There were no
significant differences in soil densities among treatments.

The plot was harvested, and the last samples taken at 2607 degree days.
The high level of terbufos md carbofuran had significantly higher root
population densities than the control. None of the three were significantly
different than the remaining treatments (Table I4). The soil population densities
of the low level of ethoprop were significantly higher than the low and high
levels of terbufos, low level of ethoprop, low level of aldicarb, and the
carbofuran treatments. The high level of aldicarb resulted in significantly lower
shelled grain yield than the other treatments. No significant difference in
moisture content of the shelled grain was observed among treatments (Table I4).
Corn rootworm (Diabrotica virgifera) adults were observed at this location.
Adults were not abundant, and did not appear to be localized within any specific

area of the plot.

3. Alan Cable corn production site

Pre-plant soil sampling at the Cable site yielded no significant differences
of soil densities of PratLlenchus penetrans among treatments (Table IS). The
first post-plant samples at the Cable site were taken at 3l5 degree days. The
root population densities of the fonofos treatments were significantly higher
than the medium md high levels of ethoprop, low and high levels of aldicarb, and
low and high levels of carbofuran (Table I6). The low and high levels of aldicarb
had significantly lower population densities than the control, high level of

terbufos, and fonofos. The soil population densities of the chlorpyrifos were

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69

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70

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71

Figure l2. Shelled grain yield versus root population density of
Pratylenchus penetrans at harvest for the Alan Cable corn
production site.

 

Figure l3. Shelled grain yield versus root md soil population density
of Pratylenchus penetrans at harvest for the Alan Cable
corn production site.

Shelled Grain Yield (BU/A)

Yield (shelled weight BU/A)
150

155

72

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73

Figure l4. Shelled grain yield versus root population density of
Pratylenchus penetrans at harvest for the Hal Benn corn
production site.

Figure l5. Shelled grain yield versus root and soil population density
of Pratylenchus penetrans at harvest for the Hal Benn corn
production site.

74

0.95

 

 

 

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o .

g ' r ' ' I ' ' ' f I ' l

0 200 ‘00 800 800
P. penetrans (root + soil) 0 Harvest

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75

Figure l6. Shelled grain yield versus root population density of

Pratylenchus penetrans at harvest for the Floyd Baum
corn production site.

Figure l7. Shelled grain yield versus root and soil population density

of Pratylenchus penetrans at harvest of all three corn
production sites.

76

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77

significantly higher than the high level of terbufos md the high level of aldicarb
(Table IS). The next samples were taken at I778 degree days. There were no
significant differences in the root population densities among treatments. The
soil density of the fonofos treatment was significantly higher than the high level
of aldicarb md high level of carbofuran.

Grain was harvested, and the last samples taken at 2295 degree days.
Fonofos, chlorpyrifos, and the control had significantly higher root population
densities than the low md high levels of aldicarb md the high level of carbofuran
(Table l6). The root population densities of these treatments did not differ
significantly from the remaining treatments. Fonofos treatments had higher soil
population densities than the low and high levels of aldicarb (Table l5). No
significant differences in shelled grain yield or moisture were observed among
treatments. '

Regressions of the numbers of Pratylenchus wetrans in roots md soil at
harvest versus grain yield were relatively inconclusive at the Alan Cable (Figures
l2 and l3) and Floyd Baum production sites (Figure l6). The R2 of these
regressions explained very little of the total variation about the mean yield. The
95% confidence bands about these regression lines were well separated, and lines
with either positive or negative slope could conceivably exist within them.

The regressions at the Benn site had much better R2 values, and there was
a decreasing relationship between numbers of E. wetrans in root and soil at
harvest in relation to yield (Figures l4 md IS). The 95% confidence bmd on the
regression line at this site was narrow and indicated a negative slope of the
regression line.

When final soil and root population densities of all three corn production

78

sites at harvest were plotted versus yield, a decreasing relationship was
observed. However, the R2 again did not explain much of the total variation
about the mem yield (Figure l7), and the 95% confidence bands were quite well

separated.

V. DISCUSSION
A. Michigm Field Corn Survey

Surveys of Michigm potato md dry bean production areas have indicated
that plant parasitic nematodes are commme associated with these crops.
Pratylenchus spp. and ILIenchorhynchus spp. were the most common nematodes
observed in dry bean production areas. fl. @etrans was the most predominant
Pratylenchus spp. observed in dry bem fields (Elliott I980). E. pgetrans is also
the predominant species of Pratylenchus recovered from potato roots and soil in
Michigm, although E. crenatus md E. neglectus were also observed (Bernard
I974, Bird I975).

The malysis of the information contained in these surveys was limited to
calculation of the percent occurrence of given nematode taxa within a sampling
region. The malyses used for the Michigm corn survey attempted to examine
the information collected in a more informative manner. Absolute frequency
md relative frequency were calculated for each of the nematode genera
observed. Frequency is a measure of distribution,'and yields no information
about abundmce (Norton I978). Relative frequency expresses absolute
frequency on the basis of the total possible sum of frequencies for all genera as
being l00%. The frequency of occurrence of a nematode in relation to other

nematodes is not altered by the choice of frequency measure (Norton I978).

79

Density is a measure of abundance, and represents the number of entities
in a given sample. Absolute density is simply the total number of taxa in a
sample, while relative density expresses density relative to the total number of
individuals of all taxa (Norton I978).

Density md frequency information are combined in the prominence value
measure. The logical basis of this measure is that frequency modifies density
through space (Norton I978). This type of measure is of interest to
nematologists in that it contains information on density which is of practical
value in damage threshold analysis. Knobloch and Bird (I978) used prominence
values and importmce values to evaluate species occurrence and population
densities of various nematode taxa in a I6.4 ha area of the Michigan State
University Water Quality Research Site.

The nematode genera found associated with field corn in Michigm
represent a complement of the more common plant-parasitic nematodes found in
Michigan (Knobloch md Bird, l98l). Plant parasitic nematodes on record as
associated with field corn in Michigm include: Pratylenchus metrans, E.
scribneri, Helicotylenchus nmnus, Tylenchorhynchus spp., and Xiphinema
americanum (Knobloch and Bird l98l).

Pratylenchus spp. were the most common plant-parasitic nematodes

 

recovered from the Michigan field corn survey. This is not surprising considering
the wide host range of Pratylenchus spp., and their relatively ubiquitous
distribution in Michigm (Knobloch and Bird, l98l). The remaining plant-
parasitic nematodes recovered varied in their relative frequencies md
prominence values from region to region. The fact that they were higher in

these two measures than the root-lesion nematode in only three counties

indicates the importance of Pratylenchus spp. in relation to field corn production
in Michigan (Table I7).

Longidorus spp. were not observed. This is the result of several factors.
The sieves employed to separate particulate matter from soil samples would
inevitably also remove these large nematodes from the samples. The survey was
performed during the late summer and Longidorus is reported as moving to lower
soil strata during this time. Longidorus breviannulatus is most frequently
associated with soils which have a sand content of 90% or higher (Malek, gt a_l.,
I980). Very few of the samples in the Michigan survey came from fields with
this high a sand content. Thus, the combination of the sampling methods and soil
processing would lead to the exclusion of Longidorus from the estimates of the
plant parasitic community (Malek gt g_l. I980).

Seasonal degree-day accumulations generally were advanced enough for
nematode reproduction to have resulted in greater nematode population densities
than were present at planting. The degree day accumulations were similar for
each county within a region, allowing evaluation of regions as units (Figure 5).

Measures of association between nematodes have not been used in
nematode ecology. If particular nematode taxa exhibit specific types of
associations with other taxa, an understanding of the relationship could be of
importance in the analysis of crop loss assessment in agricultural production
systems. Seldom are plants subject to parasitism by a single nematode species.
Several different species are usually present, and the combined effects of the
nematodes present may exacerbate crop loss in comparison to infections
comprised of fewer species. Associations between taxa may indicate what types

of ecological relationships exist between them. Such relationships could possibly

81

 

 

 

 

 

 

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82

be used in a predictive capacity within a given agroecosystem. If a particular
taxon is present it may be possible to estimate the probability of the presence of
an associated taxon. The extent to which a given taxon contributes to plant
disease is variable, and may depend on the composition of the concomitantly
infecting plant parasitic nematode community. Thus, the elucidation of the
relations between members of the nematode community could increase the
understanding of nematode-induced plant disease.

Nematode communities may be very rigidly structured, or they may be
loosely structured. The results of the survey suggest that the nematode
interactions in the soil matrix surrounding the plant root are not a type of
obligate symbiosis, but rather a result of the native populations reacting to the
local physiography and imposed cropping system.

The lack of consistent associations among nematode species observed in
these studies is not surprising. The significant associations which were observed
between taxa, on a regional and statewide basis, involve taxa which are primarily
ectoparasitic. These association values are not dramatic, and indicate a very
slight positive association. This may be a result of host modification by one
taxon which is beneficial to another taxon. This is purely speculation, as there
are a number of equally feasible hypotheses which would explain such a
phenomenon. Further experimentation would be required to determine the basis
of the apparent associations. It is possible that the observed associations are
simply reflections of the relationship of both taxa to an unobserved factor.

In agricultural systems a relatively consistent pattern of host availability is
established. Thus, the interaction between host and parasite is of prime

importance. The lack of consistent significant associations may indicate that for

83

the plant parasite community, the role of interspecific competition in limiting
the success of a specific nematode within a monocultured cropping system is nil.

The associations between predatory nematodes and plant-parasitic genera
are so variable that drawing specific conclusions on the associations is tenuous,
if not impossible. This makes sense, as all predatory nematodes are not
obligatorily nematophagous, and may thus be acting as opportunists within the
nematode community.

The range of soil types on which high population densities of Pratylenchus

spp. md TLlenchorhynchus spp. were found was not distinctly different from that

 

of low population densities of the same nematodes. The soil types in which high
population densities of Helicotylenchus spp. and Paratylenchus spp. were found
did not differ from the soil types in which high and low densities of
Tylenchorhynchus spp. and Pratylenchus spp. were found. Each of these taxa
were found on a rather narrow range of soils: loam, loamy sand, smdy loam,
sand, sandy clay, and clay loam (Figures 6-l I). This reflects the ability of the
nematodes in question to survive under the same range of soil conditions which
dictate the suitability of an area for corn production. The alteration of a natural
environment to m agricultural monoculture is a tremendous selection pressure.
It is possible that those nematodes in the natural environment which could
survive the transition to monoculture are also the "typical" plant-parasitic forms
found associated with monocultured crops. If a particular set of environmental
conditions in Michigan can support field corn production, it is probable that these
same conditions are intrinsically satisfactory for a range of specific nematode
communities. From the set of possible nematode communities which could arise

under these conditions, a subset community is actually realized, the exact

composition of which is determined by the specific subset of conditions (biotic
and abiotic environmental) which exists at a specific location. This allows for a
certain diversity of communities, and variation in community structure among
samples. This variation is masked when communities are analyzed over large

geographic areas which are relatively homogeneous.

B. Nematode Population Management Trials

The chemical treatments applied at the Benn location were chosen on the
basis of their specificity. The treatments were expected to have a variable
impact on different members of the soil community. It was hoped that this
method would allow some insight into the importance of the plmt-parasitic
nematodes inrelation to other potential yield-reducing organisms. The following
rationale was used for selection of these pesticides.

l. Methyl bromide was chosen on the basis of its effectiveness in
reducing population levels of a wide variety of potentially yield-
reducing organisms. It was expected to reduce or eliminate '
populations of soil fungi, soil insects, nematodes and bacteria.

2. Phenamiphos is a highly effective contact nematicide with excellent
persistence and ability to move with soil moisture. An
orgmophosphorous compound, it is a potent acetylcholinesterase
inhibitor (Ware I978). It does not release easily from its physiological
binding site on acetylcholinesterase, and is highly toxic. It is a
systemic pesticide, and has some ability to control sucking insects
(McEwen md Stephenson I979).

3. A pentachloronitrobenzene (PCNB) and thiazole combination was

85

chosen on the basis of its fungicidal activity. This combination
material disrupts the protein synthesis and metabolism of fungi.
PCNB is generally fungistatic, reducing growth rates md sporulation.
Thiazole is a chelating agent, affecting enzyme activity (Ware I978).
F usarium spp., a stalk rot pathogen, and Eythium spp., responsible for
seed rots and seedling blights, are both susceptible to this material.
There are many species of nematode-destroying fungi. The fungal
antagonists of nematodes belong to widely divergent orders md
include nematode-trapping fungi, endoparasitic fungi, parasites of
nematode eggs, and fungi which produce metabolites toxic to
nematodes (Mankau I980). Eythium spp. have been described as
endoparasites of free-living nematodes. It is not known if these
particular fungi parasitize plant parasitic nematodes (Tzean md Estey
l98l). The application of PCNB and thiazole was used to reduce
population densities of some plant-pathogenic fungi, nematode-
destroying fungi, md possibly, mycorrhiza.

Carbofuran is a commonly used carbamate insecticide. It has
nematicidal properties when applied at higher rates. The carbamate
pesticides have the same mode of action as the organophosphorous
pesticides, but do not bind as tightly to acetylcholinesterase.
Recovery from several sub-lethal doses is possible (McEwen md
Stephenson I979). Two rates of carbofuran were applied at the Benn
site to determine the possible advantage of using the higher

nematicidal application rate in a production system.

Nematode population fluctuations over time were similar at all three corn

86

production sites. Two population density peaks were clearly discernible at the
Benn location. This has been observed with Pratylenchus penetrans (Miller et al.
I963). The first population peaks were observed at approximately 400 degree-
days at each of the plot locations. The exact physiological temperature
dependence of the first peak cannot be determined from these data. However,
the agreement between locations indicates that 400 degree-days is a good
approximation. The second population density peak observed at the Benn site was
at 2600 degree-days. The Benn site was sampled more frequently than the other
locations, and the second population peak was not observed at the other
locations. It probably occurred between the last two sampling periods.

The first root population density peak represents the hatch of eggs as soil
conditions improved. As expected, the soil population density peaks were
temporally opposed to the peaks in the root populations. The increase in root
populations was preceded by a decline in the soil population density. Larvae
move from the soil to the roots, penetrate, and establish feeding sites (Miller 3
91. I963). There was some discrepancy between the magnitude of the numbers in
the soil when compared with the numbers in the root during these oscillations.
The endoparasitic niche occupied by the nematode does not lead to expectation
of numbers in the soil which would equal those in the root. It is possible that
those nematodes which were in close proximity to the root were not recovered
by the soil extraction procedures.

The measurement of plant heights at the Benn site indicate that methyl
bromide had an impact on plant growth by 750 degree days. The increase in
height could have been due to reduction of the nematode poplations early in the

season (Figures l8 and I9, Table II). It is equally possible that the methyl

87

Figure l8. Pratylenchus penetrans population density fluctuations
per gram of root relative to pesticide application at the
Hal Benn corn production site.

 

Figure l9. Pratylenchus gnetrans population density fluctuations
per IOO cubic centimeters of soil relative to pesticide
application at the Hal Benn corn production site.

etrans / 100 cc soil

2.

2- 20043.”. / 9mm root

2900

A

IMO
I .

 

 

 

88

0 Methyl Bromide
n Phenamiphos

I PCNB G: Thiazole
e Carbofuran (low)
. Carbofuran (high)
I Control

 

 

 

 

 

 

 

   

 

eT—f ' I ' T
D :000 3000
Degree Days (base 10 C)
§
0 Methyl Bromide
I Phenamiphos
I PCNB a: Thiazole
. Carbofuran (low)
s Carbofuran (high)
§ I Control
N.
8
O f v I v v 0
0 1000 2000 3000

Degree Days (base 10 C)

89

bromide simply resulted in increased soil ammonium levels, providing the plants
increased nutrient availability. Plant growth stimulation with methyl bromide
soil fumigation in the absence of pathogens has been reported. The growth
response is the result of decreased extant pathogen population levels, and
increased availability of nitrogenous compounds as microbial degradation of
organic material proceeds (Millhouse and Munnecke, I979).

The population levels of E. wetrans were reduced by the methyl bromide
application, but they were not eliminated“ (Figures l8 and I9). Subsequent to the
first small population density peak, the population densities remained fairly
stable and very low (Figure l8). This suppression was probably not the result of a
biological control phenomenon. Those organisms which would have exerted such
a pressure on the nematode populations should have been reduced to very low
levels by the initial methyl bromide application. Predator-prey theory predicts
that the application of mortality factors which influence both predator and prey
will result in 01 increase of the prey population while the predator population
declines (May I976). The increase of toxic nitrogenous compounds previously
mentioned may play a role in the supression of the nematode population levels.
Correlations of decline in E. @etrans populations and the microbiological
degradation of organic material with the release of nitrogenous compounds has
been reported (Walker I969).

The efficacy of carbofuran in controlling nematode population densities
was dependent on the application rate. At all sites the high rate of application
resulted in decreased initial root population peaks and decreased root population
densities, which persisted over the remainder of the season (Figures I8, 20 md

26). The persistence of this material in the soil is relatively good (Ware I978),

 

90

Figure 20. Pratylenchus penetrans population density fluctuations
per gram of root relative to pesticide application at the
Alan Cable corn production site.

 

Figure 2|. Pratylenchus penetrans population density fluctuations
per IOO cubic centimeters of soil relative to pesticide
application at the Alan Cable corn production site.

 

 

°Y_f'VT'VVvv'v
0 500 1000

 

91

é
] . e Fonofoe

‘- Chlorpyrifos
I Terbufos (high)

0 Carbofuran (high)
I Control

 

v W

3303' ziso'o"'zioo
mom(m100)

it

2
l I Fonofoe
. Chlorpyrifoe
‘ . I Terbufos
: o Carbofuran
‘ I Control
84

A_L-l

_E. metrone / 100 cc eoII

A

L

 

 

 

) /

4K\

1 1” '
2d /

/

l /
o ' *1 ' r' ' r' ' 'r’r 'V‘" at r '**' l

0 500 1000 1500 2000 2500

Degree Days (base 10 C)

92

Figure 22. Pratylenchus penetrans population density fluctuations
per gram of root relative to pesticide application at the
Alan Cable corn production site.

Figure 23. Pratylenchus penetrans population density fluctuations
per IOO cubic centimeters of soil relative to pesticide
application at the Alan Cable corn production site.

93

I Terbufos (low)

- Terbufos (high)
. Carbofuran (low)
‘ 6 Carbofuran (high)

‘ I Control

 

 

 

Degree Days (base 10 C)

 

 

 

 

al
‘ I Terbufos (low)
I Terbufos (high)
H e Carbofuran (low)
0 Carbofuran (high)
I I Control
a g-
8 ‘ /
8 I ./
\
CI
2
B
’6
c
0
. 9.“
°-l
: ...,..-.,....,..-r,-...,
0 500 1000 1500 2000 2500

Degree Days (base 10 C)

94

Figure 24. Pratylenchus penetrans population density fluctuations
per gram of root relative to pesticide application at the
Alan Cable corn production site.

Figure 25. Pratylenchus penetrans population density fluctuations
‘ per IOO cubic centimeters of soil relative to pesticide
application at the Alan Cable corn production site.

J

100
1

f. e_engtrane / gram root

 

 
 

€95

Ethaprop (low)
Ethoprop (med)
Ethoprop (high)
Aldicarb (low)
Aldicarb (high)

INODIO

Control

 

 

 

"I
800

000 2500

1000 1500 2
Degree Daye (base 10 C)

Ethoprop (low)
Ethoprop (med.)
Ethoprop (high)
Aldicarb (low)
Aldicarb (high)

INC...

Control

 

' ' V I V T I Y Y ' V I ' r V V ' Y ' ‘ V I
000 1000 1000 2000 2500

DegreeDaye(baee10C)

96

and this may account for the suppression of late season population levels. The
combination of persistence and the higher application rate would result in
increased residuals md activity over the course of the season. The low rate of
application did not suppress the late season population density increase. The
inability of the lower rates to produce a season-long effect is probably the result
of dilution and degradation of the toxin. Pratylenchus vulnus exposed to low
concentrations of carbofuran recover their ability to disperse when the toxin is
removed from their environment (Marban-Mendoza and Viglierchio l980a).

The application of carbofuran is known to inhibit motility, dispersion, and
attraction to roots of Pratylenchus 1u_ln_us_. This interferes with egg production
and transitions between life stages (Marban-Mendoza and Viglierchio l980a). In
addition, carbofuran affects the dispersion of second stage larvae more severely
than the adult stage, and the percent penetrating the root is reduced as the
concentration of the material is increased (Marban-Mendoza and Viglierchio
l980c). The orientation and movement of _F_’_. metrans md Tylenchorhynchus
clay_toni have been shown to be affected by the nemastatic properties of
carbofuran (Diszo I973).

Carbofuran application at the Cable and Baum sites produced results
similar to those at the Benn site (Figures l8-2l, 26 and 27). The suppression of
the soil and root populations subsequent to the first population density peak was
not as pronounced. This may have been due to a number of physiographic factors
which differed among sites. Carbofuran probably reduced the root populations of
the nematodes through the combination of toxicity, inhibition of infective stages
in finding feeding sites, and inhibition of reproduction.

The application of PCNB and thiazole at the Benn site did not result in

97

Figure 26. Pratylenchus penetrans population density fluctuations
per gram of root relative to pesticide application at the
Floyd Baum corn production site.

 

Figure 27. Pratylenchus penetrans population density fluctuations
per IOO cubic centimeters of soil relative to pesticide
application at the Floyd Baum corn production site.

penetrane / gram root

 

f.

60
1

A

98

Ethaprop (low) /
Ethoprop (med.)
Ethoprop (high) /
Aldicarb (low)

Aldicarb (high) /
Control

I N to 9 II e

/

 

 

 

. enetrans / 100 cc eoll

P
2'0

 

 

 

V""—l_'-T_Y—ft"rtlj'"l""1
500 1000 1500 2000 2500 3000
Degree Daye(bme10 C)

Ethoprop (low)
Ethoprop (med.)
Ethoprop (high)
Aldicarb (low)
Aldicarb (high)
Control

IMO...

 

r...,...-,-...,....,....,....1
500 1000 1500 2000 2500 3000
DegreeDaye(baee10C)

99

significant increases in nematode population densities in soil or root when
compared to the control. This indicates either that PCNB and thiazole were not
toxic to those fungi present, or the role played by nematophagous fungi in
controlling population densities at this site was minimal. As there is no
information available on the toxicity of this material to nematophagous fungi in
general or with reference to specific genera, either hypothesis remains a
possibility. The lack of yield increase in the PCNB + thiazole treatments
indicates that either the population densities of the plant pathogenic fungi
present were inconsequential or the level of control achieved for the plant
pathogenic fungi present was inconsequential.

Phenamiphos application at the Benn site resulted in trends similar to that
of the high rates of carbofuran. This was expected considering the length of
time phenamiphos remains active in the soil, and the broadcast method of
application. Phenamiphos is similar to carbofuran in its inhibition of egg
production, motility, and attraction to plant roots (Marban-Mendoza and
Viglierchio l9800). Phenamiphos has been observed to reduce numbers of _P_.
muons md Fusarium spp. infections in alfalfa (Willis and Thompson I979).
Populations of Pratylenchus spp. are reported to be reduced on field corn by
phenamiphos (Norton et al. I978).

Phenamiphos is more effective than carbofuran in reducing motility of E.
vu_lr1§ when the two materials are applied at the same rates. The concentrations
of phenamiphos which result in irreversible physiological changes in E. w
motility are much lower than for carbofuran (Marban-Mendoza and Viglierchio
I980). The chemoreceptor and coordination pathways in _P_. WE are much

more sensitive to phenamiphos than to carbofuran (Marban-Mendoza and

100

Viglierchio l980b).

The application of fonofos and chlorpyrifos at the Cable site did not
significantly affect soil or root population densities. Neither material is
officially labeled as having nematicidal properties. Chlorpyrifos has been
reported as having a weak nematicidal effect (Smolik I978). The lack of
nematicidal activity with respect to nematodes may be due to a lack of systemic
activity (Ware I978).

Terbufos, ethoprop and aldicarb were among the chemical nematicides
tested at the Baum and Cable sites. It is interesting to note that the population
density fluctuations as influenced by ethoprop and aldicarb were very similar at
these sites (Figures 20-29). The trends in percent control of _P_. wetrans
achieved by these treatments is in good agreement with the work of Norton et
al. (I978) which deals with the some materials controlling. Pratylenchus spp.
associated with Iowa field corn.

At the Cable md Baum sites the general trends in percent control in
decreasing order were: aldicarb (high), aldicarb (low), ethoprop (high), ethoprop
(med.), ethoprop (low), terbufos (high), and terbufos (low). Norton et al. (I978)
found the same general trend except that terbufos achieved control greater than
my of the levels of ethoprop. Aldicarb was expected to achieve excellent
nematode control as it is known as a very potent carbamate nematicide. It has .
been shown to reduce movement and induce convulsions in Aphelenchus avena
(Keetch, I974), and to reduce egg hatch, migration, and mating in Heterodera .
schachtii and Meloidogme iavanica (Hough and Thomason I975, Osborne I973).
Aldicarb may be especially effective in controlling Pratylenchus penetrans due

to the movement of the material and its sulphoxide metabolites within the roots

101

Figure 28. Pratylenchus penetrans population density fluctuations
per gram of root relative to pesticide application at the
Floyd Baum corn production site.

Figure 29. Pratylenchus penetrans population density fluctuations
per IOO cubic centimeters of soil relative to pesticide
application at the Floyd Baum corn production site.

 

netrans / 100 cc soil

 

pe

_P.

102

P.

 

 

 

s
r I Terbufos (low)
I Terbufos (high)
4. Carbofuran
I Control
-3 f
.. I /
§
g l \ /
3
? -§l \ /
g l \ /
c I \ /
l I /
. /
/
\
Ari ,_ ‘7'
0 ‘ 000 1000 1000 3000'”th
MI- ouy- (bale 10 0)
in I Terbufos (low)
\ I Terbufos (high)
’ I Carbofuran
-\ - Control

 

 

 

I
3000

Degree Days (baee 10 C)

103

of plants (Osborne I973). This could reduce mating and the establishment of
feeding sites through inhibition of coordinated muscular activity. These factors
would account for the effective nematode population density reduction with this
material at the Cable and Baum locations.

The high rate of terbufos resulted in significant root nematode control at
the Baum site, but did not at the Cable site. This difference may be due to
physiographic differences between sites, or may be the result of a type one
error.

Ethoprop did not result in significant population density alteration in soil or
roots at either location. This is surprising as the label declares the material to
have good residual activity, md it has been reported as having efficient
nematicidal activity (Norton et al. I978). It has been reported that ethoprop
does not persist in soil as long as had been previously thought (Rohde et al. I980).

Chemical nematicides vary in their efficacy in reducing root and soil
population densities of nematodes. Only circumstantial evidence on the mode of
action of these materials in relation to plant-parasitic nematodes is available.
The in viig studies conducted on nematicides are usually limited to a narrow
range of concentrations, and the applicability of the results to a field situation is
uncertain (Hough and Thomason I975). The subtle effects of nematicides on
nematode behavior at low concentrations are not known. The persistence of
nematicidal materials in the soil depends on many factors including:
formulation, substrate used for granular materials, volatility of the chemical
toxicant, soil pH, soil temperature, soil type, soil moisture content,
photodegradation, microbial degradation, and leaching (McEwen and Stephenson

I979). Considering the range of factors impacting on the final efficacy of a

104

given material in a specific field situation, it is difficult to arrive at a final
analysis which is much more than an educated guess. The fact that the results
from the Baum, Benn, and Cable sites are in accord on many points is support for
the thesis that some insight into application of these chemical nematicides in
Michigan has been gained.

The lack of significant yield differences at the Benn and Cable locations
may be the result of several factors. One possibility is that nematodes did not
impact severely on corn at the population densities observed. If this was the
case, controlling these levels would not be an economically sound management
option. Population levels similar to those encountered at the Benn site have
been observed to cause damage to field corn (Norton et al. I980). It is
interesting to note that each of the farm mmagers who cooperated in these
studies annually applies a corn insecticide to control corn rootworm.

If the results of these experiments were hypothetically interpreted on the
basis of corn rootworm control, the lack of significant yield differences suggests
that- such a practice is prophylactic. A possible explanation of the lack of yield
differences is inadaquate replication. Further replication might have provided a
reduction in the variance of the data, allowing discrimination of effects on final
yield.

Moisture stress has been shown to exacerbate nematode damage to crops
(Barker I978). All three test sites had adequate 'moisture. Figure 30 shows
cumulative precipitation versus degree day accumulation at the Benn site. This
figure can be considered representative of all the sites. The plethora of rainfall
during the I980 growing season in central Michigan may have resulted in highly

virorous root system development in the field corn in this study. These root

105

Cumulative Precipitation (cm.)
20.0 25.0 30.0
I L J g L L A I L A

5.0 10.0 15.0
l l I A l A L A l L A A

A

 

 

0.0

T r T r f r f 1 r r r l r I v I
0 500 1000 1500 2000 2500 3000 3500 4000
Cumulative Deg. Days (base 10 C)

Figure 30. Cumulative precipitation versus degree day accumulation
at the Hal Benn corn production site.

106

systems would have been able to support large population densities of nematodes
without significant damage.

The lack of significant regressions at the Alan Cable and Floyd Baum
production sites may be explained by the relatively low harvest population
densities at those sites when compared to the Hal Benn production site. These
regressions suggest that it may be possible to obtain damage threshold densities
at harvest, which could then be related to pre-plant densities using estimates of
population increase over the course of the season. This would be a difficult task,
and reliable estimates of damage thresholds are not yet available (Norton I979).
Variations in soil types and local climes contribute to the difficulties in assess-

ing crop loss due to plant parasitic nematodes.

Vl. SUMMARY

Plant parasitic nematodes are commonly associated with field corn in
Michigan. The taxonomic composition of the nematode'community associated
with field corn is variable; however, Pratylenchus spp. are the most common and
typically have the highest density. The population densities of plant parasitic
nematodes observed associated with field corn in Michigan are theoretically high
enough to cause disease resulting in yield loss.

Trials of nematicidal chemicals which reduced the densities of plant
parasitic nematodes under field conditions did not result in significantly
increased corn grain yields. It is possible that com plants supplied with adequate
soil moisture can tolerate relatively high population densities of plant parasitic
nematodes. Further research is required to obtain reliable estimates of

nematode damage thresholds in relation to field corn.

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Johnson, A.W., and C.J. Nusbaum. I968. The activity of I. claztonii,
Trichodorus m E. brachyurus, E. w, and Helicotylenchus dihystera
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l4:9.

Jugenheimer, R.W. I976. Corn improvement, seed production, and uses. John
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Kable, P.F., and W.F. Mai. I964. lngress of E. penetrans into alfalfa roots in
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Kaplan, D.T., R.A. Rohde, and T.A. Tatter. I976. Leaf diffusive resistance of
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soils. Nematologica l 7:308- l 8.

113

Kisiel, M., K. Deubert, and B.M. Zuckerman. I969. The effect of
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97.

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114

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115

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Nematol. 7: | 68-7 I.

 

116

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Ponchillia, P. E. I972. Xiphinema americanum as affected by soil organic
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Peet, R.K. I974. The measurement of species diversity. Ann. Rev. Ecol. and
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Pielou, E.C. I974. Population aid Community Ecology, Principles md Methods.
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117

Powell, N.T. I963. The role of plant parasitic nematodes in fungus disease.
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Proctor, J.R., and C.P. Marx. I974. The determination of normalizing
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Puffinberger, C.W. l98l. Pest detections in Maryland. Maryland Dept. of
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Riedel, R.M., M.J. Brown, S.R. Shafer, and M.A. Heinlein. I980. From NC-I47
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Rome, C.W. I973. Trends in breeding for disease resistance in crops. Ann.
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Rogers, R.R., and J.C. Owen. I974. Relationship of carbofuran treatment to
agronomic traits in maize. J. Econ. Ent. 67:557-58.

.Romm, J. md H. Hirschmm. I969. Morphology and morphometrics of six
species of Pratylenchus. J. Nematol. I:363-86.

Seinhorst, J.W. I970. Dynamics of populations of plant parasitic nematodes.
Ann. Rev. Phytopath. 8:I3I-56.

Sikora, R.A., D.P. Taylor, R.B. Malek, and DJ. Edwards. I972. Interaction of
MeIoi e £51, Pratylenchus penetrans, and Tylenchorhynchus ggr_i on
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Smolik, J.D. I978. Influence of previous insecticidal use on the ability of
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118

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Tarte, R. and W.F. Mai. Morphological variation in E. metrans. J. Nematol.
8:I85-95.

Taub, F .R. I974. Closed ecological systems. Ann. Rev. Ecol. and Syst. 5:|39—
60.

Taylor, D.P., and W.R. Jenkins. I957. Variation within the nematode genus
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Thistlethwayte, B. I970. Reproduction of E. penetrans (Nematoda). J.
Nematol. 2:IOl-5.

Townshend, J.L. I972. Influence of edaphic factors on penetration of corn roots
by Pratylenchus penetrans and E. M in three Ontario soils.
Nematologica I8:202-I2.

Townshend, J.L. I973. Survival of E. metrans md E. m in twoOntario
soils. Nematologica I9:35-42.

Townshend, J.L., and L.R. Webber. I97I. Movement of E. wetrons and the
moisture characteristics of three Ontario soils. Nematologica l7:47-57.

Thomas, S.H. I978. J. Nematol. l0:24-27.

Thomason, I.J., and F .C. O'melia. I962. Pathogenicity of E. scribneri to crop
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Tzem, 5.5., and R.H. Estey. l98l. Species of Phytophthera md hium as
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119

Wallace, H.R. I97I. Abiotic influences in the soil environment. Plant Parasitic
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Wallace, H.R. l97l. The influence of the density of nematode populations on
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Wallace, H.A., and W.L. Brown. I956. Corn and Its Early Fathers. Michigan
State Univ. Press, East Lansing.

Walker, J.T. I969. Pratylenchus penetrans (Cobb) populations as influenced by
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Walker, J.T. l97l. Populations of E. penetrans relative to decomposing
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Walker, J.T., C.H. Specht, and J. Bekker. I965. Nematicidol activity against _.
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55:l3l.

Wong, K., and J.M. Ferris. I968. Factors influencing the population fluctuation
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Young, P.A. I953. Damage caused by meadow nematodes to corn in east Texas.
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Young, P.A. I964. Control of corn nematodes with Vorlex and DD. Plant Dis.
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Yule, G.U., and M.G. Kendall. I968. An Introduction to the Theory of Statistics.
Hafner Publishing Co., New York.

Zirakparzar, M.E., D.C. Norton, and C.P. Cox. I980. Population increase of E.
hexincisus on corn as related to soil temperature and type. J. Nematol.

l2:3I3-I8.

 

120

Appendix A. Nematode root extraction technique (after Bird I97 I).

 

Shaker Technique. The root incubation shaker technique was used to recover

endoparasitic nematodes from 2.0 grams of root tissue from each sample.

Equipment: Gyratory shaker, 250 ml flask, ethoxyethyl mercuric chloride, and

dihydrostreptomycin sulfate (EMC-DSS), IOO and 400-mesh sieve, test tubes.

Procedure:

(I)
(2)
(3)

(4)
(S)

(6)
(7)

Wash roots and cut into l-2 cm segments.

Place a random sample of root tissue (2.0 g) in a 250 ml flask.

Cover tissue with a mixture of IO ppm ethoxyethyl mercuric chloride md
50 ppm dihydrostreptomycin sulfate (ca. 75-l00 ml).

Incubate at |00 rpm for 48-72 hours.

Rinse incubation solution from nematodes into chemical waste container
through a I00-mesh screen over a 400-mesh screen.

Pour nematode suspension from 400—mesh screen into labeled test tube.
Store at IS C until microscopic evaluation for quantitation md qualitation

of population characteristics.

121

Appendix B. Soil extraction technique (after Caveness and Jensen I955).

 

I. Centrifugation-flotation Technique. The centrifugation-flotation

 

technique is commonly used to extract eggs and vermiform nematodes and

spores of endomycorrhizal fungi from known quantities of soil. Nematodes

and spores living within plant roots cannot be obtained using this technique.

a. Equipment: Centrifuge with horizontal (swinging-out bucket) head to

run at a relative force of 420 g; 25-mesh, IOO-mesh and 400-mesh

screen; l00 ml beaker (plastic); pails; test tubes.

b. Chemicals: Sucrose solution, specific gravity = I. I4

c. Procedure:

(I)
(2)

(3)

(4)

(5)

(6)
(7)

Mix soil thoroughly.

Place 0 I00 cm3 sub-sample into a plastic pail and add sufficient
water to fill l/2 to 3/4 of the pail.

Stir for I0 seconds breaking up clumps of soil and allow soil to
settle for ID seconds.

Decant supernatmt onto a 25-mesh screen placed over a 400-
mesh screen.

Discard debris collected on 25-mesh screen.

Pour washings from 400-mesh screen into 50 ml centrifuge tubes.

Place tubes in centrifuge. Stir each tube well.

(8)
(9)
( I0)

(ll)

(I2)

(I3)

(I4)

122

Centrifuge at 420 g for 412 minutes.

Decant water from tubes (discard supernatant).

Fill centrifuge tubes with regular sugar solution. Mix each tube
well.

Suspend soil pellet in centrifuge tube.

Centrifuge for I.5 minutes at 420 g.

Decant sugar solution-nematode supernatmt onto a I00 over a
400-mesh sieve, and wash the nematodes to remove the sucrose.
Rinse residue md nematodes from the 400-mesh sieve into a

labeled test tube using a small funnel.

123

Appendix C. Cole's measurement of interspecific association (1949).

 

 

 

SPECIES B
+ -

+ a b a + b = m
<:
U)
I.”
I3
8
u: - b d C + d = n

a + C = r b + d = S m + n =1o-+ S = T

 

 

 

Species A is designated as that species which was least
frequent in the series of collections [i.e., (a + b) §_(a + c)]

 

 

 

 

 

ad“: bc; c = ad - bc i o = (a + c) (c + d)
fi+bfl6+d7 C Tra+birb+cn
ad < bc and a 5_d; c = ad - bc i o = _jb + d) (c + d)
mw + C T(a+b) (a+ c)
ad < bc and a > d; c = ad - bc 4
z 0 = (a + b) (a + C)
””75““ C TW+d)(c+d)

124

Appendix [1 Absolute frequencies, relative densities and prominence
values of four plant parasitic nematodes associated with
152 corn production sites in 38 Michigan counties.

 

Relative défiSity

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Absolute per 1.0 gm root& Prominence
gounty frequency (%) 100C} soil (%) value
ALLEGAN

Pratylenchus spp. M68.8 45.8 326.8
Helicotylenchus spp. 18.8 20.7 77.2
Tylenchorhynchus spp. 37.5 27.9 146.9
Paratylenchus spp. 18.8 1.9 6.9
ALPENA
Pratylenchus spp. 100.0 84.1 532.0
Helicotylenchus spp. - - -
Tylenchorhynchus spp. 12.5 8.9 19.8
Paratylenchus spp. 25.0 2.5 8.0
ANTRIM
Pratylenchus spp. 100.0 71.8 598.0
Helicotylenchus spp. - - -
Tylenchorhynchus spp. 6.3 5.8 12.0
Paratylenchus spp. 25.0 14.4 60.0
ARENAC
Pratylenchus spp. 87.5 72.4 961.6
Helicotylenchus spp. 62.5 11.5 129.7
Iylenchorhynchus spp. 18.8 4.5 27.7
Paratylenchus spp. 62.5 7.0 79.1

 

125

Appendix 0. (cont.)

 

Relative density

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Absolute per 1.0 gm root& Prominence
gounty frequency (%)f lOOc? soil (%)7 value
BAY
Pratylenchus spp. 62.5 66.8 725.7
Helicotylenchus spp. 25.0 14.6 100.0
Tylenchorhynchus spp. 6.2 0.3 1 0
Paratylenchus spp. 43.8 17.5 158.8
BERRIEN
Pratylenchus spp. 75.0 44.3 135.1
Helicotylenchus spp. 18.8 40.9 62.4
TyJenchorhynchus spp. - - -
Paratylenchus spp. 18.8 3.4 5.2
BARRY
Pratylenchus spp. 87.5 85.8 927.9
Helicotylenchus spp. 25.0 10.7 62.0
Iylenchorhynchus spp. 25.0 1.7 10.0
Paratylenchus spp. 6.3 0.7 2.0
BRANCH
Pratylenchus spp. 100.0 90.9 8390.0
Helicotylenchus spp. 56.3 7 1 492.2
IyJenchorhynchus spp. 12.5 1 2 39.6
Paratylenchus spp. 6.3 0.1 1.0

 

126

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix D. (cont.)
7' "7Re1ative density 7
Absolute per 150 gm root& Prominence
County frequency (z), 100c 5011 (%)A value
CHARLEVOIX
PratyJenchus spp. 100.00 64.4 580.0
Helicotylenchus spp. 75.0 8.8 69.3
Tylenchorhynchus spp. 37.5 3.1 17.1
Paratylenchus Spp. 37.5 2.7 14.7
CLINTON
Pratylenchus spp. 100.00 78.2 1562.0
Helicotylenchus spp. 12.5 0.4 2.8
lxlenchorhynchus spp. 50.0 13.0 183.8
Paratylenchus Spp. 50.0 5.8 82.0
DELTA
Pratylenchus spp. 87.5 79.9 1592.1
Helicotylenchus spp. 43.8 16.2 227.5 ,
Tylenchorhynchus spp. 18.8 0.9 8.6
Paratylenchu§_spp. 37.5 1.1 14.7
DICKINSON
Pratylenchus spp. 93.8 82.6 1264.5
Helicotylenchu§_spp. 56.3 6.6 78.0
Iylenchorhynchus spp. - - -
Paratylenchus spp. 31.3 1.5 13.4

 

127

Appendix 0. (cont.)

 

RelatiVe density

 

 

 

 

 

 

 

 

 

 

 

 

 

Absolute per 1.0 gm root& Prominence
County frequency (%) l00c3 soil (%) value
GRAND TRAVERSE
Pratylenchus spp. 100.00 82.2 1488.0
Helicotylenchus spp. 26.7 5.9 54.8
Tylenchorhynchus spp. 13.3 1.5 10.2
Paratylenchus spp. 13.3 0.4 2.9
GRATIOT
Pratylenchus spp. 93.8 39.7 776.5
Helicotylenchus spp. 18.8 22.4 195.7
Iylenchornynchus spp. 31.3 11.7 131.9 _
Paratylenchus spp. 56.3 -8.1 123.0
HILLSDALE
Pratylenchus spp. 93.8 59.1 548.0
Helicotylenchus spp. 43.8 28.0 177.3
Tylenchorhynchus spp. 18.8 6.2 25.9
Paratylenchus spp. 18.8 1.3 5.2
HOUGHTON
Pratylenchus spp. 100.0 97.8 1080.0

 

Helicotylenchus spp. - - _
Tylenchorhynchus spp. - - _

Paratylenchus spp. - - -

128

Appendix 0. (cont.)

 

Relative density

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Absolute per 1.0‘gm root& Prominence
County frequency (%) 10003 soil (%) value
HURON
Pratylenchus spp. 87. 28.7 .94.6
HelicotyJenchus spp. 62. 43.0 246.7
Tylenchorhynchus spp. - - -
Paratylenchus spp. 25. 3.9 14.0
10500
Pratylenchus spp. 100. 86.6 696.0
Helicotylenchus spp. - - -
Tylenchorhynchus spp. - - -
Paratylenchus spp. 31. 10.0 44.7
JACKSON
Pratylenchus spp. 100. 97.6 4940.0
Helicotylenchus spp. - - -
Tylenchorhynchus spp. 6. 0.6 7.0
Paratylenchus spp. 43. 0.8 26.5
KENT
Pratylenchus spp. 75. 94.8 190.5
Helicotylenchus spp. - - -
Tylenchorhynchus spp. - - -
-Paraty1enchus spp. 6. 1.7 1.0

129

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix D. (cont.)
- Relative density
, Absolute per 1.0 gm root& Prominence

County frequency (Z) lQQé’ ng1 (z) value

LAPEER
Pratylenchus spp. 100.0 55.9 624.0
Helicotylenchus spp. - - -
Tylenchorhynchus spp. 31.3 15.0 93.9
Paratylenchus spp. 37.5 17.6 120.0

LEELANAU

Pratylenchus spp. 100.0 89.3 1668.0
Helicotylenchus spp. 12.5 0.4 2.8
Tylenchorhynchus spp. 6.3 0.9 4.0
Paratylenchus spp. - - -

LENANEE
Pratylenchus spp. 68.8 10.8 87.9
Helicotyjenchus spp. 37.5 82.4 497.2
Tylenchorhynchus s-p. 6.3 1.2 3.0
Paratylenchus spp. - - -

MACKINAC

Pratylenchus spp. 87.5 98.1 1953.1
Helicotyjenchus spp. - - -
Tylenchorhynchus spp. 6.3 0.2 1.0
Parathlenchus spp. 6.3 0.6 3.0

130

Appendix. 0. (cont.)

 

Relative density

 

 

 

 

 

 

 

 

 

 

 

 

 

Absolute per 1.0 gm root& Prominence
County Ereguency (%) 100c3 soil (%) value
MENOMINEE
Pratylenchus spp. 100.0 78.0 898.0
Helicotylenchus spp. 68.8 8.3 79.6
Tylenchorhynchus spp. 6.3 0.7 2.0
Paratylenchus spp. 12.6 1.0 4.2
MISSAUKEE
Pratylenchus spp. 100.0 86.3 1212.0
Helicotylenchus spp. - - -
Tylenchorhynchus spp. 6.3 0.3 1.0
Paratylenchus spp. 68.8 7.4 86.2
MONROE
Pratylenchus spp. 37.5 6.6 22.0
Helicotylenchus spp. 62.5 24.1 104.4
Tylenchorhynchus spp. 56.3 26.3 108.0
Paratylenchus spp. 12.5 2.2 4.2
MONTCALM
Pratylenchus spp. 100.0 95.7 2048.0

 

Helicotylenchus spp.

 

Tylenchorhynchus spp.

Paratylenchus spp.

131

Appendix 0. (cont.)

 

‘Relative density

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Absolute per, 1.0 gm r00t& Prominence
County frequency (%)y 100c3 soil (%)f Value
MUSKEGON
Pratylenchus spp. 93.8 35.8 848.3
fielicotylenchus spp. 31.3 1 0 13.4
Tylenchorhynchus spp. 50.0 54.0 939.0
Paratylenchus spp. 43.8 1 8 29.0
NENAYGO
Pratylenchus spp. 93.8 93.3 540.3
Helicotylenchus spp. - - -
Tylenchorhynchus spp. 18.8 4.0 10.4
Paratylenchus spp. - - -
OGEMAN
Pratylenchus spp. 93.8 75.8 850.1
Helicotylenchus spp. 18.8 6 6 32.9
Tylenchorhynchus spp. 18.8 2 1 10.4
Paratylenchus spp. 31.3 5 2 33.5
PRESQUE ISLE
Pratylenchus spp. 100.0 94.7 972.0
Helicotylenchus spp. 6.3 1.2 3.0

 

Tylenchorhynchus spp. - - -
Paratylenchus spp. 25.0 3.7 19.0

132

Appendix 0. (cont.)

 

Relative density

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Absolute per 1.0 gm root& Pr0minence
.Coynrtv frgqusepwgyfl‘ 100a? soil (%) value
SAGINAN
Pratylenchus spp. 87.5 22.5 431.2
Helicotylenchus spp. 93.8 54.7 1084.4
Tylenchorhynchus spp. 50.0 17.0 246.0
Paratylenchus spp. 56.3 1.4 21.0
SANILAC
Pratylenchus Spp. 87.5 51.1 215.1
He1icoty1enchus spp. 18.8 3.6 6.9
Tylenchorhynchus spp. 37.5 12.4 34.3
Paratylenchus spp. 18.8 6.2 12.1
TUSCOLA
Pratylenchus spp. 81.3 39.2 183.8
Helicotylenchus spp. 25.0 6.2 16.0
Tylenchorhynchus spp. 12.5 4.6 8.5
Paratylenchus spp. - - -
NASHTENAN
Pratylenchus spp. 88.9 85.2 1214.3
Helicotylenchus spp. 33.3 6 6 57.7
Tylenchorhynchus spp. 38.9 6 1 57.4
Paratylenchus spp. 1.1 0.5 0.8

133

Appendix E. Insecticide-nematicides applied in I980 field trials.

 

TEMIK‘ ISG (Aldicarb) Union Carbide Chemical Compmy
LORSBAN' ISG (Chlorpyrifos) Dow Chemical Company

MOCAP‘ ISG (Ethoprop) Mobil Chemical Company

NEMACUR‘ ISG (Phenamiphos) Mobay Chemical Compmy
TERRACLOR SUPER-X' (PCNB & Thiazole) Olin Chemical Company
COUNTER' I5G (Terbufos) American Cymamid

DYFONATE' IOG (Fonofos) Stauffer Chemical Company

FURADAN' IOG (Carbofuran) FMC Corporation

METHYL BROMIDE (Bromo-methone) Great Lakes Chemical Company

134

Appendix F. Mechanical Soil Texture Analysistudrometer Method.

 

l0.

Weigh 50 9 air dry soil or I00 9 for coarse texture or sandy soil.

Transfer to dispensing cup.

Add I00 ml 5% calgon (50 g/Iiter). Fill cup about half with distilled water.
Stir using the electrically driven mixer for IS minutes.

Transfer the suspensions to the graduated cylinder and fill to marked
volume of I I30. If a IOO 9 sample is used, fill to volume of I205.

Remove the hydrometer.

Record temperature of suspension. Insert the plunger and move it up and
down to mix the contents thoroughly.

Lower the hydrometer carefully into the suspension and read after 40
seconds.

Remove hydrometer carefully, rinse the surface and wipe it dry. Take
hydrometer reading again after 2 hrs. Insert hydrometer carefully into
suspension I0 seconds before measurement. Record temperature.

Make temperature correction before doing calculation.

Temperature Correction:

0) Add .36 to hydrometer reading for each degree above 20 C.

b) Deduct .36 from hydrometer reading for each degree below 20 C.

Calculations:

95 5m + clay = First hydrometer readLnQ (corrected x I00)

 

 

Sample weight
9e, clay = Second hydrometer reading (corrected x I00)
Sample weight
96 sand = I00 = 96 silt + clay (first reading)
%silt = I00-(96 smd +%clay)

HIGRN STATE UNI V LI