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This is to certify that the

thesis entitled

WHOLE PLANT MEASUREMENT OF PHOTOSYNTHESIS
AND DEVELOPMENT OF APPLE TREES
IN RELATION TO PEST DAMAGE

presented by

Sarah Lynn Breitkreutz

has been accepted towards fulfillment
of the requirements for

M. S. degree in Horticulture

 

 

 

002M WM
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Major professor

Date April 14, 2000

 

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WHOLE PLANT MEASUREMENT OF PHOTOSYNTHESIS AND
DEVELOPMENT OF APPLE TREES IN RELATION TO PEST DAMAGE

By

Sarah Lynn Breitkreutz

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Horticulture

2000

ABSTRACT

WHOLE PLANT MEASUREMENT OF PHOTOSYNTHESIS AND
DEVELOPMENT OF APPLE TREES IN RELATION TO PEST DAMAGE

By
Sarah Lynn Breitkreutz

The objectives of this study were to determine the relationship between whole
plant photosynthesis (WPP) and overall growth of apple trees as influenced by
the damage caused from insects and disease. WPP was measured on sixty four
apple trees of varieties ‘Empire’ and ‘Liberty’ seven times during the 1997
growing season on trees subjected to six pesticide and fungicide treatments.
Results showed a decrease in the rate of WPP as the season progressed for all
treatments from a maximum of 1-5 umol COz-cm'2 TCSA-s’1 to a minimum of <
0.5 umol COz'Cm-z TCSA-s". The soft IPM treatments had higher rates of
photosynthesis than other treatments during June when the photosynthetic rate
was near maximum. WPP was found to be correlated with total foliar damage on
three dates of damage assessment for non-barrier ‘Empire' and one date for
‘Liberty’. Yield was greater for the barrier plot than the non-barrier plot (0.86 and
0.79 kg-cm'2 TCSA) and greater for ‘Empire’ than ‘Liberty’. In light of the
interesting results observed in the photosynthesis between the soft chemicals
and the conventional chemicals we repeated the study with potted apple trees.

We observed similar results to the field experiment at three sampling dates.

Dedication

This thesis is dedicated to Great Grandma Brazee. I wish she could have been

here to see this.

ACKNOWLEDGMENTS

I would sincerely like to thank Mark Kelm for his love, support and
friendship. Mark, you’re the best! I would also like to thank Mom, Tom, Liz,
Grandma Gavitt, Dad and Anita for their encouragement and support.

I wish to thank all of my friends and oo-workers. Each of you have added
so much to my life not only in terms of priceless help with my project but more
importantly with valuable conversation and friendship. In particular, I would like
to thank Rebekah, John 3., Beth, John L., Matt, Brie, Allison, Stephanie and
Colin who helped me with countless tasks sometimes not so fun, but always with
a smile. I would also like to thank all of the students and post-docs in our
laboratory Leo, Costanza, Rita, Abed, Adriana, and Zafer. Thanks also goes to
the wonderful staff at the plant and soil science building and at CHES Kristi,
Julie, Sherry, Gabrielle, Lorri, Joyce, Jerry, Case, Donna, Shelly, Peach and
John. Thanks to all my dear friends Tom, Erik, Priscilla, Russel, Andy, Bill,
Jennifer, Hongying and Joe who are always ready to listen and were there when
I needed you.

Sincere thanks also goes to my committee members Dr. Jim Flore, Dr.
Ron Perry and Dr. Mark Whalon. In particular, I wish express my thanks to my
major professor Jim, who has not only been a great teacher, but a good friend. l
have learned so much through this experience and hope to have the opportunity

to continue to work with all of you in the future.

TABLE OF CONTENTS

LIST OF TABLES ................................................................................................. vi
LIST OF FIGURES .............................................................................................. vii
LIST OF ABBREVIATIONS ................................................................................ viii
SECTION I ............................................................................................................ 1
REVIEW OF LITERATURE ................................................................................... 2
SECTION II ......................................................................................................... 16
INTRODUCTION ................................................................................................. 17
MATERIALS AND METHODS ............................................................................ 20
RESULTS ........................................................................................................... 33
DISCUSSION ...................................................................................................... 48
SUMMARY AND CONCLUSIONS ...................................................................... 56
REFERENCES .................................................................................................... 57

LIST OF TABLES

Table Page

Table 1. Pest and pathogen control for barrier and non-barrier plots, at IPM
apple orchard site in CHES, Clarksville, MI, 1997 ..................................... 23

Table 2. Dates that whole plant photosynthesis was measured and the
environmental conditions on those dates ................................................ 38

Table 3. Correlation between foliage damage and whole plant photosynthesis
for ‘Empire’ and ‘Liberty’ apple using linear coefficient of determination (r2), for
IPM plots, CHES, 1997 ........................................................................ 41

Table 4. a)Average yield per TCSA and % fmit > 130 g for barrier and non-
barrier plot and ‘Empire’ and ‘Liberty’. b)Average yield per tree and % fruit >
130 g for apple IPM plots, CHES, 1997 ................................................... 43

Table 5. a)Whole plant photosynthesis for potted apple trees. b)Single leaf
photosynthesis for potted apple trees. c)Shoot number and average shoot
length for potted apple trees. Means on the same date followed by the same
letter are not significantly different (Duncan‘s test p 5 0.10) ......................... 47

vi

LIST OF FIGURES

Figure Page
Figure 1. Plot plan for non-barrier and barrier plots at CHES, Clarksville, MI
1997. r=’ldared', e=‘Empire’, and l=’Liberty’ ....................................... 21

Figure 2. Spectrum for Mylar® ......................................................... 25
Figure 3. Two whole plant photosynthesis chambers ............................ 27

Figure 4. Whole plant photosynthesis per cm2 TCSA measured during the
1997 growing season for non-barrier plot varieties ‘Empire’ and ‘Liberty’.
Vertical bars indicate standard
error ........................................................................................... 34

Figure 5. Whole plant photosynthesis per m2 leaf area measured during the
1997 growing season for non-barrier plot varieties ‘Empire’ and ‘Liberty’.
Vertical bars indicate standard error .................................................. 36

Figure 6. Total foliar damage for three dates in 1997 determined by the
addition of individual damages from mines, Iepidoptera, aphids and bronzing
and burning .................................................................................. 39

Figure 7. Foliar damage Vs whole plant photosynthesis for non-barrier and
barrier plots varieties ‘Empire’ and ‘Liberty’ .......................................... 40

Figure 8. Fruit size Vs average yield per tree for non-barrier and barrier
plots varieties ‘Empire' and ‘Liberty’ for 1997 ...................................... 44

Figure 9. Yield per tree per TCSA and whole plant photosynthesis for non-
barrier plots, varieties ‘Empire’ and ‘Liberty’, CHES, 1997 ..................... 45

vii

LIST OF ABBREVIATIONS

CHES - Clarksville Horticultural Experiment Station
CMD - Cumulative Mite Day

002 - Carbon dioxide

DAFB — Days After Full Bloom

Epan — Class A Pan Evaporation

HRTC — Horticultural Research Teaching Center
IPM — Integrated Pest Management

I RGA — Infrared Gas Analyzer

PAR — Photosynthetic Active Radiation

PLC - Parkinson Leaf Chamber

ppm — Parts Per Million

PVC — Polyvinyl Chloride

TCSA - Trunk Cross Sectional Area

WPP — Whole Plant Photosynthesis

viii

SECTION I

REVIEW OF LITERATURE

Review of Literature

As agriculture developed, humans remodeled the landscape significantly
by encouraging some animals and plants to multiply and others to be displaced.
The result was local areas with reduced biological diversity and a greater
confrontation of humans with insects. Subsequently, when agriculture developed
and greater areas of land were utilized for farming, pressure from insect
populations increased disproportionately, making pest control a major
preoccupation (Pedigo, 1999). The Sumerians are reported to be the earliest to
implement pest control strategies with the use of sulfur about 2500 BC
Egyptians and Chinese used herbs and oils as insecticides for the protection of
seeds and stored grain (Pedigo, 1999). In the 19th century, methods to control
orchard pests were lead arsenate and sulfur compounds. Although effective in
killing pests, these compounds proved to be extremely toxic to humans (National
Research Council, 1993).

Modern use of insecticides began with the advent of 1,1-Bis (4-
chlorophynyl)-2,2,2-tricioroethane (DDT) in 1946 (Poehling, 1989). The harmful
effects of DDT and its persistence in the environment became known over time,
which lead to the revocation of DDT in 1972 (National Research Council, 1993).
Synthetic pyrethroid compounds began to be used in the 1980’s The advantages
were that they offered much the same protection as DDT but could be applied in
much smaller amounts (gm rather than kg-acre“), and that they broke down in
the environment (National Research Council, 1993). However, one of the

problems with using pyrethroid compounds is that they are indiscriminate

2

insecticides, killing both beneficial and non-beneficial insects. This disrupts the
natural balance of predators and prey in the orchard. Researchers observed the
detrimental effects of broad spectrum pesticides such as the development of
resistance to formerly lethal compounds, previously harmless pests becoming
major pests and people’s awareness and concerns with pesticide residues in
their produce and their possible harmful effects (Croft, 1978). Further
disadvantages with broad spectrum pesticides were biomagnification of
pesticides in the food chains, and increased cost for production of crops due to
increased costs of pesticides (Watson et al., 1975).

Many of these environmental problems have arisen because many
horticultural crops such as apples are long term perennial crops. Orchards are in
the same location for many years and with repeated application of pesticides,
fungicides and herbicides there is an accumulation of chemicals that persist in
the soil. Also, apple orchards are usually located near large bodies of water such
is the case in Oregon, Washington, Michigan and New York because of the
favorable climate and good drainage in these locations. This can lead to
magnification of the impact of orchard pesticides on these associated water
systems (Croft, 1978).

Integrated pest management

Integrated pest management (IPM) is the practice of manipulating insect
or disease pest populations using ecologically sound methods of control to keep
these pests at levels below that which would cause economic injury (Watson et

al., 1975). The increased use of IPM strategies has been brought about for three

main reasons: 1) insect and disease resistance to pesticides, 2) consumer
demands for insecticide residue free foods and 3) the loss of the use of existing
chemicals because of federal regulations (Subrahanyam and Hagstrum, 1996).
As the name implies, IPM practices involve chemical controls, biological controls
and cultural practices. Biological controls consist of: predators, parasites and
pathogens (VanLenteren, 1989). The objective of a biological control is either to
introduce natural enemies or to manipulate existing ones to cause the pest
population to fall to a density below the economic-injury level (Pedigo, 1999). A
goal of many biological control programs is to create a self-sustaining system.
This means that there has to be a balance maintained between the natural
enemy and the pest. The pest can’t be completely eliminated because this would
deplete the source of food for the natural enemy. Therefore a balance must be
struck between the populations of the natural enemy and the populations of the
pest (Pedigo, 1999).

One of the first IPM programs was developed in Nova Scotia in 1942.
Export restrictions forced apple growers in this region to implement a program
that reduced pesticides. They attempted to regulate natural pest populations and
limited the use of selective insecticides such as Ryania, nicotine, and lead
arsenate. The adoption of this new system saved the industry in Nova Scotia
(Whalon and Croft, 1984).

A major concern when reducing chemical input in orchards is to ensure
that fruit quality is not compromised. One percent damaged fruit is the maximum

allowed for all pest and non-pest related sources for fresh market in the United

States (Croft and Hoyt, 1983). There are four categories for apples in the US.
(US. extra fancy, U.S. fancy, U.S. No.1 and US. utility). For an apple to be
classified as extra fancy, it must meet the following criteria: mature but not
overripe, clean and well formed. Free from decay, internal browning, internal
breakdown, scald, scab, bitter pit, Jonathan spot, freezing injury, visible water
core, and broken skins and bruises. Free from injury caused by smooth net-like
russeting, sunburn or spray burn, limb rubs, hail, drought spots, scars, disease,
insects, damage by smooth, solid, slightly rough or rough russeting or stem or
calyx cracks, and free from damage by invisible water core after January 31‘"t of
the year following the year of production. In addition, each apple of this grade
must have the amount of color specified in table 51.305 for the variety. (Code of
Federal Regulations, 1996). Because of this low tolerance, IPM practices are
difficult to use.

For IPM to be successful, it has to be economically feasible. Managing an
orchard should include attention to all major types of pests (insects, diseases,
weeds and vertebrates) and their principal natural enemies. Farmers need to
know what insects and diseases are problems in their location and the life cycles
of these pests. IPM requires much more technical expertise than spraying
chemicals according to a schedule. The grower needs to know precisely what
the pests are doing, in addition, they need to know which beneficial insects are
present and how to manage these populations by modifying pesticide

applications (Croft, 1978).

Management of the habitat encompassing the orchard is very important.
This habitat is comprised of soil, trees, ground cover and the vegetation and
nonliving matter surrounding the orchard. The proximity of plants harboring key
orchard pests can have a profound effect on the probability of key pests
Immigrating into and colonizing an orchard (Prokopy, 1994).

IPM has been equated to steps of a ladder. The first of those steps being
control of a single class of pests using ecologically sound methods. The second
is the integration of multiple management practices across all classes of pests.
The third step of the ladder is the integration of IPM for all classes of pests with
all the horticultural practices used on a farm. Finally the fourth step is the
blending together of concerns about pest management of all the interested
parties including researchers, extension personnel, private consultants, industry,
growers, processors and distributors, consumers, neighbors of growers,
environmentalists and local as well as federal government regulatory agencies
(Prokopy et al., 1994).

When determining where we are today in terms of implementing the four
levels of IPM designed by Prokopy, it would probably have to be said that we are
still on stage one of trying to control single classes of pests. There are several
reasons for this which have to do with government policies influencing farm
profits, insurance and credit. Also the economic viability of alternative techniques
such as yield and profits, the size of the farm, and the increased labor and
management needed for alternative techniques (McDonald et al., 1994). In

addition, there are the farmer’s preconceptions about alternative means of

growing. Recent studies have shown that most farmers have incorporated some
form of IPM into their orchard practices. A survey of growers in the New England
area reported that 73% of apple growers currently scout for insects and disease
before spraying chemicals. In addition, 15% of apple growers in New York
reported using all of the IPM methods available for their crop (McDonald et al.,
1994). However, even though this sounds promising, many farmers do not wait
for thresholds to be reached before spraying the crop (McDonald et al., 1994).
Damage Thresholds

Damage threshold is defined as the amount of injury that justifies some
from of control measures. Economic threshold and action threshold are both
defined as the amount of damage that justifies the cost of artificial control
measures. These thresholds are usually expressed as a number of insects per
area, plant or sampling procedure. Less commonly these levels are expressed
as degree of plant damage or combinations of numbers and damage (Pedigo,
1999). Pests that feed on the foliage are particularly suitable to IPM practices
(Francesconi, et al., 1996a). Damage thresholds are difficult to determine
because of many factors such as the leaf to fruit ratio, weather, variety, time of
year, and tree vigor.

Timing and severity of injury is very important in the development of
damage thresholds. Early defoliation of spur leaves in apples was found to
reduce fruit set and fruit development (Ferree and Palmer, 1982). Lakso (1984)
showed that defoliation of spur leaves results in severe reductions in fruit set

while defoliation of shoot leaves have relatively little effect. Removing spur

leaves later in the season [after 30-50 days after full bloom (DAFB)] has no effect
on fruit size (Rom and Ferree, 1986). Infection from diseases can effect
photosynthesis. Powerdy mildew (Podosphaera Ieucotn’cha) caused a 75%
reduction in photosynthesis at 35 days after infection. Apple scab (Venturia
inaequalis) caused a 20% decrease in photosynthesis (Ferree et al., 1986).
Infestation by mites was found to cause reduction in photosynthesis. A
population of 60 mites per leaf caused a significant reduction in apple
photosynthesis three days after placement on the leaf. Nine days after infection,
15 mites per leaf reduced photosynthesis by 26%, 30 mites per leaf by 30% and
60 mites per leaf by 43% below the value observed in uninfected controls (Ferree
et al., 1986). Francesconi et al. (1996b) found an interaction between cumulative
mite day (CMD) and reduction in fruit weight from trees with high CMD and
normal crop load. Weddle (1990) looked at the balance of beneficial predator
mites to phytophagous mites and found that a ratio of 2:10 was sufficient to
reduce the number of miticide sprays applied. Weddle also looked at the timing
of pesticide applications. He found that spraying for pear psylla (Homopter:
psyllidae) in the dormant season controlled pear psylla for the season without
killing beneficial arthropods that would normally have been killed by the chemical
if applied later in the growing season.

In addition to the habitat surrounding the orchard and the pests in the
orchard, it is important to understand the horticultural practices that can aid in
pest management. For example. maintaining tree stability in the soil to promote

the establishment of a strong root system, ensuring that there is adequate

nutrient and moisture availability for tree and fruit growth, and pruning trees in a
way that optimizes fruit yield and quality (Prokopy, 1994). All of these factors
give rise to a tree that is in good physiological status.

Some problems with damage thresholds are that they are poorly defined
or not available. The variations in the thresholds comes from differences in
sampling techniques, pest status, market parameters, management options, time
of year of control, orchard history, and human factors (eg. perception of pest and
management philosophy) (Whalon and Croft, 1984). For example, Prokopy et al.
(1997) explained that monitoring of tentiform leafminer is dependent upon which
generation you want to control (there usually being three generations per year).
The most popular is to look for mines on leaves. This is a good method for post
petal fall application of pesticide but too late for petal fall or pre-bloom
applications which destroy adults, eggs and sap feeding larvae. They found that
pre-bloom captures of leafminer adults were useful predictors for growers to
determine if action in the form of chemical sprays needed to be taken or not.

Monitoring for disease should be based on the right conditions for the
disease to develop. Apple scab is a good example of this. The use of spore
traps and various weather instruments makes it possible to monitor both the scab
fungus and the climatic factors inducing infection. Therefore, when the apple
scab ascospores are detected and the right weather conditions develop sprays
can be applied and if those conditions don’t develop, then the sprays can be
avoided (Jones, 1974). One problem with monitoring and spraying pesticides for

individual pests is the effect on other pests beneficial or non-beneficial. When

applying fungicides, the targeted disease is not the only one affected. For
example, some fungicides have an effect on mite populations, killing beneficial
mites (Jones, 1974).

Simulated pest injury or stress can be a very good tool for understanding
the periods of the growing season that are particularly sensitive to decreases in
photosynthesis and also in developing damage thresholds. Disegna (1994)
studied the effect of Sinbar (an herbicide that interrupts the flow of electrons from
photosystem II to photosystem I) applied to apple trees at different times in the
growing season and at different concentrations. He found that at 15 and 30
DAFB, mm were induced to abscise. This was greater for trees having a high
crop load. Inhibition of photosynthesis at 30, 60, 80, and 100 days after full
bloom reduced return bloom. Partial defoliation below a certain threshold may be
overcome by plant photosynthetic compensation. Evidence shown by Layne and
Flore (1992) in cherry showed that up to 20% of leaf area could be removed
between veins without reducing whole leaf photosynthesis. Hall and Ferree
(1976) found that reductions in apple leaf area up to 7.5% had no effect on
photosynthesis, however when leaf area losses exceeded 10%, significant
reductions in photosynthesis were observed.

The use of models can be helpful in determining damage thresholds and
make IPM more accessible to the grower. Developing a model for disease and
pests would give up to date information to growers to make day to day decisions
on disease and pest control. The data from these models has to be reliable and

current. For example fungicides for scab control (a major disease of Michigan

10

apples) must be applied 24-36 h from the beginning of a wetting period (Jones,
1976). PETE (Predictive Extension Timing Estimator) was one of the first models
for generalized individual phenology timing. This model sought to improve
phenology predictions of pest developmental stages based on synchronization
with biological monitoring information from the field (Whalon and Croft, 1984).
Whole plant photosynthesis

As discussed above there is need for more accurate ways to determine
damage thresholds especially for secondary pests that feed only on the foliage of
the crop. One tool used to estimate the effect of damage done by foliage feeders
is to measure the photosynthetic capacity of the leaves. This can be done on the
single leaf or the whole plant level. Previously whole plant photosynthesis
systems were cumbersome and rarely portable. With the advent of new
materials such as Mylar", movement of the system from one tree to the next has
become much easier. There are many benefits in measuring whole plant
photosynthesis rather than single leaf photosynthesis. The main reason is due to
the variation between leaves in a canopy. When measuring single leaf
photosynthesis, only a selection of leaves can be measured on a tree which have
to be extrapolated to the encompass photosynthesis of all leaves on the tree.
This can lead to over or under-estimation of the photosynthetic capacity of the
entire tree. WPP is the integration of photosynthesis of all the leaves on a tree
and respiration by branches, and fruit.

Whole plant photosynthesis (WPP) rates are much lower than those for

single leaf for many reasons. One is due to leaf age. In a tree canopy there are

11

newly formed leaves that have not yet reached their maximum photosynthetic
capacity, fully expanded leaves at their full photosynthetic potential and older
leaves that have begun the process of senescence (Poni et al., 1994a).
Differences in angles of incident radiation vary depending on the position of the
leaf, whether it is at the top or bottom of the canopy or on which side of the tree.
These differences lead to different levels of photosynthesis (Flore and Lakso,
1989). In addition, if the leaf is on the inside of the canopy or the outside there
are differences in the amount of light received due to shading effects (Flore,
1994). The respiration of vegetative and reproductive tissues also must be
considered when determining whole plant photosynthesis (Corelli-Grappedelli
and Manganini, 1993). Another factor causing variation in photosynthesis among
leaves on a tree is crop load. The amount of fruit per tree or absence of effects
photosynthesis. Whether the crop load is high or low will make a significant
difference on the rate of photosynthesis (Lakso et al., 1996). Also the proximity
of carbohydrate sinks and other source-sink relationships play a role in the rate
of photosynthesis for a leaf (Edson, 1995). Fujii and Kennedy (1985) observed
that after canopy development, there are higher rates of photosynthesis in fruiting
trees than non-fruiting trees during the period of rapid increase in fruit growth.
Also, toward the end of vegetative period the leaves of fruit-bearing shoots
showed a slightly higher rate of photosynthesis, whereas, leaves of shoots
without fruits showed a reverse trend (Ghosh, 1973). Grape vines showed a
decline in photosynthesis earlier In the day for non-fruiting vines possibly

resulting from carbohydrates building up faster in the non-fruiting vine due to

12

feedback inhibition (Downton et al., 1987). There are also biotic and abiotic
stresses that play a role in the rate of photosynthesis for a leaf such as insects,
cultural practices, water deficiency or water excess. As demonstrated by the
examples above it can be extremely difficult to extrapolate the gas exchange for
a single leaf to that of the whole plant.

Heinicki and Childers (1937) were of the earliest to measure WPP. They
realized that the measurement of a single leaf or part of a leaf was not
representative of the entire plant. With this knowledge they designed a chamber
to contain an apple tree and measured the daily photosynthesis for an entire
growing season. They found that the plant reached a high rate of photosynthesis
early in the season and a maximum rate of photosynthesis was reached while
new leaves continued to develop and grow. They also found that the rate of
photosynthesis for the whole tree was considerably less than the average based
on determinations of single leaves exposed to good light. They estimated that
90% of the total leaves were functioning at a very low rate on many days during
the growing season. In addition, they found that with greater transpiration, there
was less photosynthesis. With light conditions the same in July and August, there
was more photosynthesis in July than August. This they thought was because
the plant was losing too much water during the hot part of the summer and
closing the stomata during the hot part of the afternoon.

In a similar study Giuliani et al. (1997b) looked at the canopy level
relationships between diurnal trends of environmental variables and

photosynthetic and transpirational activities and the control exerted by plant

13

factors on these responses. They observed the WPP of a fruiting and a non-
fruiting apple tree to see how source-sink relationships affect the regulation of
whole canopy gas exchange. They found that the light-saturated net
photosynthetic rates were higher for the fruiting canopy than for the non-fruiting
canopy. Also there was a decrease in the aftemoon, particularly for the non-
fruiting canopy. They believed that the afternoon decrease in photosynthesis
was not regulated by stomata as Heinicki and Childers thought, but rather by
some other factors, perhaps feedback inhibition. Canopy conductance was
higher for. the fruiting canopy than the non-fruiting canopy. From this they
concluded that canopy conductance may actively regulate photosynthetic activity
and may also be modulated by feedback control in response to assimilation
capacity. They concluded that adjustments in canopy conductance, which were
partially dependent on the vegetative-reproductive status of the tree, control the
equilibrium between photosynthesis and transpiration.

A study by Francesconi et al. (19963) showed that the physiological status
of the plant plays an important role in its ability to overcome pest infestation. For
example, lightly cropped trees were able to deal with mite infestations better than
normally cropped trees as the normal cropped trees showed a reduction in fruit
weight with increased mite injury.

For all of the benefits of measuring whole plant photosynthesis there are
drawbacks as well. First, the whole plant chambers can be cumbersome. Also
more time is involved with setting up the system making it impossible to make as

many measurements in one day as can be accomplished when measuring single

14

leaves. The relationship between the 002 differential for a whole tree and the
leaf area of the tree is important but very difficult to determine. For example,
when measuring older trees, it is extremely time consuming and tedious to count
the total number of leaves on the tree and measure their areas. It is possible that
whole plant gas exchange can be based on different criteria such as the amount
per plant in a given period of time (Miller et al., 1996) or on the basis of cross
sectional area of the plant or total shoot length (Palmer, 1987).

WPP can possibly be used as a tool to determine damage thresholds.
With knowledge of times during the growing season that are particularIy sensitive
to decreases in photosynthesis and the interaction with crop load we can attempt
to understand the amount of damage that can occur before the need for some

type of action.

15

SECTION II

WHOLE PLANT MEASUREMENT OF PHOTOSYNTHESIS AND
DEVELOPMENT OF APPLE TREES IN RELATION TO PEST DAMAGE

16

Introduction

Biotic and abiotic stresses can severely damage the fruit or vegetative
organs of apple trees. The amount of damage incurred by a plant before it
affects dry matter accumulation or a reduction in fruit quality is termed a damage
threshold. Economic threshold and action threshold are both defined as the
amount of damage that justifies the cost of artificial control measures (Pedigo,
1999)

Pests that attack fruit have a lower damage threshold than pests that feed
on the foliage. Therefore, a major concern when reducing chemical input is to
ensure that fruit quality is not compromised. For example, there are four grades
for apples in the US. (US. extra fancy, U.S. fancy, U.S. No.1 and US. Utility).
There are strict guidelines that must be met for an apple to be categorized as an
extra fancy explained in the Code of Federal Regulations (1996). One percent
damaged fruit is the maximum allowed for all pest and non-pest related sources
for fresh market (Croft and Hoyt, 1983). Pest management strategies which
keep fruit damage at low levels are difficult to use.

Diseases and insects that attack the foliage of a tree are especially
suitable for IPM practices if pests can be controlled after a certain tolerable level
of leaf injury occurs and before the crop is damaged (Francesconi et al., 1996a).
However, quantifying the damage caused by foliar feeders on perennial crops
like apple is difficult. There are many integrated factors which determine damage
thresholds such as environment (availability of water, nutrients and sunlight),

biotic (insects, diseases and weeds), cultural practice (pruning and spacing), and

17

physiological (vigor, crop load, and return bloom). Foliar pests effect the
production and allocation of carbon resources in the whole plant. Therefore,
duration and timing of injury are very important and may reduce the carbon
assimilation potential of the tree (Layne and Flore, 1992).

The relationship between photosynthesis and damage was observed by
Disegna (1994) in an experiment using a photosynthetic inhibitor. When applied
to apple trees at 15 and 30 DAFB, fruit abscission was induced. This was
markedly higher for trees having a high crop load vs. a low crop load, and also
significantly reduced yield and fruit size. Francesconi et al. (1996b) showed that
an increase in apple crop load was associated with an increase in sensitivity of
apple trees to high mite populations as measured by mean fruit size and crop
value. Effects of simulated insect injury to apple leaves were studied by Hall and
Ferree (1976). Losses up to 7.5% did not effect leaf photosynthesis, but above
10% significant reductions occurred. Further evidence shown by Layne and
Flore (1992) in cherry showed that up to 20% of leaf area could be removed
between veins without reducing whole leaf photosynthesis.

The need for reliable damage thresholds and the use of IPM has become
very important for three main reasons: 1) insect and disease resistance to
pesticides, 2) consumer demands for pesticide residue free foods and 3) the loss
of the use of existing chemicals due to federal regulations (Subrahanyam and
Hagstrum, 1996). The development of accurate damage thresholds can aid the

farmer in making informed decisions on when to apply pesticides.

18

The physiological status of the plant plays an important role in its ability to
overcome pest infestation. Pest damage can effect fruit development mediated
via the carbon balance of a tree (Lakso et al., 1996). WPP is an estimate of the
total net carbon uptake of whole plants and, therefore, could be used as a tool to
estimate the physiological status and damage thresholds for a plant.
Francesconi et al. (1996b) found a correlation between crop load and WPP per
fruit and showed that crop load greatly effected the sensitivity of apple trees to
European Red Mite.

The objectives of the current study were to correlate WPP with pest
damage and yield in several new pest management systems. This study was
carried out by measuring whole plant gas exchange on trees in two orchard pest

systems and assessing the foliar damage caused by pests on these trees.

19

Materials and Methods

Damage threshold research was conducted on plots designed to evaluate
whole orchard pest management systems at the Clarksville Horticulture
Experiment Station (CHES), Clarksville, MI and at the Horticulture Research and
Teaching Center (HRTC), East Lansing, MI. One main field experiment (1997
CHES) and one container-grown plant experiment (1999 HRTC) were conducted.
WPP was measured and correlated to foliar damage due to pests or to crop yield
in an effort to determine damage thresholds for apple. The plant material and
measurement techniques are described below.

1997 Experiment at CHES
Plant Material

The CHES IPM apple project was established in 1994. Two apple
varieties, ‘Empire’lM.9 EMLA and ‘Liberty’lMark (Hilltop Nurseries, Hartford, Ml),
were used in this experiment (Fig. 1). The trees were trained to a slender spindle
system. Each tree was supported by a 2.5 m metal tube and with high tensile
wire, at a 2 m height, which was anchored at both ends of each row. Eight 0.4
ha plots with 300 trees/plot were separated by at least 200 m and were divided
into two main treatments. Four of the plots were surrounded with a vegetative
barrier which consisted of hybrid poplar (Populus deltoides Bartr. X P. nigra L.),
adjacent to the apple trees, Italian alder (Alnus cordata L.), and white pine (Pinus
strobus L.), furthest from the apple trees. Four plots had no a barrier. Orchard
and barrier trees were watered with a drip irrigation system at 60% of class A pan

evaporation (Epan) throughout the season. Alley-ways in the barrier plot were

20

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planted with an endophytic grass mix, “Crusader" (Seed Research of Oregon,
lnc., Corvallis, OR), that included a rye grass inoculated with a fungal endophyte
Acremonium Iolii, which has been shown to be insecticidal (Johnson-Cicalese
and White, 1990). The non-barrier plot was established without perimeter
barriers and with standard Kentucky blue/fescue grass for sodded alley-ways.
Weed control consisted of Weedar® 64, Solicam®, and Roundup® to control
broadleaf weeds and rogue grasses. The pest management treatments were
established perpendicular to the apple variety rows.
Pest Management System in each plot

The pest management system consisted of six treatments; 1) Entomology
control in which no insecticides or fungicides were used; 2)Pathology control in
which Guthion" 50W was applied but no fungicides were applied; 3) Soft IPM
with four sprays of the fungicides Dithane® 7SDF and Elite‘3 4SDF and summer
applications of Fluazinam (a non-registered pyridine fungicide); 4) Soft IPM with
four sprays of fungicides Dithane® 75DF and Elite® 4SDF with no Fluazinam; 5)
Conventional IPM with protective fungicide Dithane® 7SDF and no Fluazinam; 6)
Conventional IPM with protective fungicide Dithane® 7SDF and summer
applications of Fluazinam. In addition, the soft IPM treatments had applications
of Confirm", Spinosad” and Provado0 1.6E.C. The conventional IPM had
applications of Lannate® 90$P, Lorsbanm 50W and Guthion® 50W. In addition,
Agri-Mycin” 17, Agri-strep", NAA and Mous—Con® were applied to all six of the

above treatments. The border trees were sprayed with Asana" (Table 1).

22

Table 1. Pest and pathogen control for barrier and non-barrier plots, at
IPM apple

orchard site in Clarksville Horticultural Research Experiment Station,
Clarksville, MI 1997.

 

 

Pestlclde Treatment
Appllcatlon Entomology Pathology Soft IPM +
Date Control Control Summer Program
21-Apr
29-Apr Elite° 4SDF, 0.27l/ha
bithane" 75DF, 2.1 kg/ha
07-May *Weedar" 64, 2.4llha *Weedar" 64, 2.4l/ha *Weedar° 64, 2.4l/ha
06-May
10-May Elite° 4501:, 0.27I/ha
Dithane" 7501:, 2.1kglha
13-May
20-May Agri-Mycin°17,1.7kg/ha Agri-Mycino17,1.7kglha Agri-Mycin°17,1.7kglha
23-May Elite" 4501:, 0.27l/ha
Dithane° 7501:, 2.1kglha
27-May
28-May Agfishep°,1.7kg/ha Agrlstrepo,1.7kg/ha Agristrep",1.7kglha
03-Jun Elite° 450F, 0.27l/ha
Dithane" 7SDF, 2.1kg/ha
04-Jun NAA, 7ppm NAA, 7ppm NAA, 7ppm
05—Jun Spinosad", 0.37l/ha
06-Jun Provado" 1.6EC,
0.35l/ha
1 1-Jun *Roundupo, 3.6llha 'Roundupo, 3.6llha 'Roundup”, 3.6llha
16-Jun Fluazinam, 0.43l/ha
26—Jun Guthion" 50w. 1.4kg/ha
27-Jun Fluazinam, 0.43llha
07-Jul Confirm", 1.33m
Fluazinam, 0.43llha
Spinosad", 0.37llha
15—Jul *Roundup", 3.6llha *Roundup", 3.6I/ha *Roundup°, 3.6llha
‘Weedar" 64, 2.4Ilha 'Weedar° 64, 2.4llha 'Weedar° 64, 2.4I/ha
18-Jul F luazinam, 0.43llha
27-Jul Fluazinam, 0.43llha
29-Jul *Roundup°, 3.6llha *Roundupo, 3.6llha *Roundup°, 3.6llha
06-Aug Fluazinam, 0.43l/ha
08-Aug Guthlon°50W.1.4kg/ha Confirm",1.33llha
20-Aug 'Roundup’, 3.6llha *Roundup", 3.6llha *Roundup", 3.6llha
26-Aug Guthion°50W,1.4kglha Confirm", 1.33llha
03-Nov ‘Roundup", 3.6llha ‘Roundup", 3.6llha *Roundup", 3.6llha
'Sollcam" 3.4kg/ha *Soricam‘D 3.4kg/ha ‘Solicam° 3.4kg/ha
24-Nov Mous-Con°,11.3kg/ha Mous-Con°,11.3kglha Mous-Con°,11.3kg/ha

 

23

Table 1.
Continued

Pestlclde Treatment

 

Application Soft IPM -
Date Summer Program

Conventional IPM 1»
Summer Program

Conventional IPM -
Summer Program

 

21 -Apr

29-Apr Elite" 4501:, 0.27llha
Dithane" 75DF, 2.1kg/ha

07-May ‘Weedar° 64. 2.4llha

06-May

10-May Ellte" 45DF, 0.27llha
Dlthane" 75DF, 2.1kglha

1 3-May

20-May Agri-Mycin017,1.7kglha

23-May Elite° 450F, 0.27I/ha
Dithane" 7501:, 2.1kg/ha

27-May

28-May Agristrepo,1.7kg/ha

03-Jun Elite° 450F, 0.27Ilha
Dlthane" 75DF, 2.1kglha

04-Jun NAA, 7ppm

05-Jun Spinosado, 0.37llha

06-Jun Provado° 1.6EC,
0.35l/ha

1 1-Jun 'Roundup°, 3.6llha

1 6-Jun

26-Jun

27-Jun

07-Jul Confirm”, 1.33m
Splnosad", 0.37llha

15-Jul 'Roundup", 3.6llha
‘Weedar° 64, 2.4llha

18-Jul

27-Jul

29—Jul ‘Roundup", 3.6llha

06-Aug

08-Aug Confirm", 1.33llha

20-Aug 'Roundup". 3.6llha

26-Aug Confirm", 1.33m

03-Nov *Roundup", 3.6llha
‘Solicam° 3.4kglha

24-Nov Mous-Con°,1 1 .3kglha

DlthanevllSDF, 4.1kglha
Dithane" 4SDF, 4.1kglha

'Weedar" 64, 2.4llha
Dithane° 4SDF, 4.1kglha

Dithane° 450F, 4.1kg/ha

Agri-Myclno 17,1.7kg/ha
Dlthane" 450F, 4.1kglha

Dlthane° 4501:, 4.1kg/ha
Agrlstrepo,1.7kglha
Dithane" 4SDF, 4.1kg/ha

NAA, 7ppm

Lannateo gasp, 1lblA

LorsbanT" 50W, ZIb/A
'Roundupo, 3.6llha

Fluazinam, 0.43l/ha

Fluazinam, 0.43llha
Guthion" 50w, 1.4kg/ha
Fluazinam, 0.43llha

*Roundup", 3.6llha
'Weedar" 64, 2.4llha

Fluazinam, 0.43l/ha
Fluazinam, 0.43l/ha
'Roundup", 3.6llha
Fluazinam, 0.43l/ha
Guthion° 50w. 1.4kglha
*Roundup°, 3.6llha
Guthion" 50w, 1.4kg/ha
*Roundup", 3.6llha
‘Solicam° 3.4kg/ha
Mous-Con",1 1 .3kg/ha

Dru-ans“ 4501:, 4.1kg/ha
Dithane" 4501:, 4.1 kg/ha

‘Weedar° 64, 2.4llha
Dithane’ 450F, 4.1kg/ha

Dithane° 45DF, 4.1 kg/ha

Agri-Mycin" 17,1.7kg/ha
Dithane" 45DF, 4.1 kg/ha

Dlthane" 450F, 4.1kg/ha
Agrlstrep",1.7kglha
Dithane" 4SDF, 4.1kg/ha

NAA, 7ppm

Lannate" 90313. 1Ib/A

LorsbanTM 50W, 2lblA
'Roundup", 3.6llha

Guthion“ 50w, 1.4kg/ha

*Roundup°, 3.6llha
'Weedar° 64, 2.4l/ha

*Roundup°, 3.6llha

Guthion" 50w, 1.4kglha
'Roundupo, 3.6llha
Guthion" 50w, 1.4kglha
'Roundup°, 3.6llha
‘Solicam° 3.4kg/ha
Mous-Con°,1 1 .3kg/ha

 

Note: Asana at .74llha was applied to vegetative barrier trees on 6/5, 7/7,
8/8. and 8/26/97.

*Roundup, Weedar and Solicam were herbicides applied to ground
beneath trees and alleyways.

24

Whole Plant Photosynthesis

Methodology: WPP was estimated using a balloon methodology as
previously reported by Miller et al. (1996) with a chamber constructed from
Mylar® designed to fit over the entire canopy of the apple tree. Mylar® was
chosen because it is lightweight, has low permeability to 002 and water vapor,
and the transmission characteristics are very similar to air through the visible
range, with nearly zero transmission below 314 nm in the UV range (E. l. du Pont
de Nemours and Company, 1999). Our light transmission experiments
supported their findings and, furthermore, we found that transmission of infrared

was nearly 100% (Fig. 2).

 

 

 

 

 

 

 

 

6
1 Sun
5‘ ‘1‘ ‘ ~
. ‘ A!‘;‘
g 4 . Mylar® ‘ AA“
‘5'.“ 3 ‘
q -1
as f1
a. 2 d
10‘ Sun-Mylar®
1 T /
. .1 v — " M_ _ “_
O r T I r r W
300 400 500 600 700 800 900 1000 1100 1200
Wavelength (nm)

 

Figure 2. Spectrum for Mylar”

25

Mylar’s® ability to transmit infrared light is Important because it prevents
heat build up inside the chamber, which is caused by trapped infrared radiation.
Additionally, MylarQ is resistant to high and low temperatures and is strong yet
flexible and puncture-resistant. A 4 m3 chamber was fitted over the entire
canopy of an apple using zippers to seal the side and top. The Mylar® chamber
was attached to a 0.28 m2 wooden circular base that was clamped around the
tree trunk with brass trunk clamps (Fig. 3). A hole was cut in the wooden base to
fit a 10.2 cm diameter piece of polyvinyl chloride (PVC) pipe with an elbow joint
fitted to a 1.2 m piece of PVC pipe. Air was circulated through the system with a
shaded pole blower model number 4COO4A (Dayton Electronic Mfg. Co., Niles,
IL) attached to the end of the PVC pipe. The speed of the fan ranged from 600-
3000 I/min and was controlled with a variable autotransformer type 3PN1010
(Staco energy Products 00., Dayton, OH).

The gas exchange for the whole tree was measured with an infrared gas
analyzer (IRGA) ADC LCA-2 (Analytical Development Co., Hoddesdon, UK.)
The amount of C02 in the air entering the chamber was measured from inside
the PVC pipe and termed the reference air. The amount of C02 in the air exiting
the chamber was measured from a 7 cm hole cut in the top of the chamber and
was termed the sample air. The air flow through the system was adjusted to stay
within 5-30 ppm A002 while still allowing for enough flow to keep the air
temperature inside the chamber from increasing (approximately three complete
air exchanges per minute). This flow rate was measured with a Tri-Sense® hot

wire anemometer (Cole Parmer, Vernon Hills, IL). The equation to estimate

26

 

Figure 3. Two whole plant photosynthesis chambers.

27

WPP was taken from Miller et al. (1996) and modified to include division by the
trunk cross sectional area (T CSA) calculated by measuring the diameter of the
trunk at 20 cm above the graft union and calculating the area for a circle. TCSA
was measured at the beginning of the growing season. Also we included
changes in molar volume for the range of air temperatures that we experienced
in the field (20-40°C). In calculating the molar volume, we assumed that
atmospheric pressure was constant over the temperature range of 20-40°C
based on the ideal gas law making volume then linearly proportional to
temperature. Molar volume is designated molar volumeT in the equation to
account for the changes with air temperature. The units for the equation are
pmol CO2-cm'2 TCSA-s". Hence, the revised equation is:
Pn(pmol C02-cm'2-s“) = (AQszL-L" x (flgzw)L-min'1
molar volumeT pL-pmol" x (TSCA)cm2 x SOs-min'1

Leaf area was calculated on a sample of 20 leaves per tree by measuring
the length of the lamina, the width at the widest region of the leaf, and
multiplying by 0.71(J.A. Flore, unpublished data). The average leaf area was
multiplied by the number of leaves on the tree to get a total leaf area. The
equation above can be used to calculate WPP on the basis of leaf area by
substituting leaf area in m2 for TSCA .

In addition to the gas exchange measurements, the incident
photosynthetic active radiation (PAR) was measured with a 1903 quantum
sensor and recorded with a Ll-1000 data logger (Ll-COR, lnc., Lincoln, NE). The

sensor was held above the canopy in a horizontal position to the ground. Air

28

temperature was measured with copper-constantan thermocouples (type T)
(OMEGA Engineering, Inc., Stamford, CT) placed at the inlet and outlet of the
chamber. Relative humidity was measured with the ADC LCA-2 Parkinson leaf
chamber (PLC) (Analytical Development Co., Hoddesdon, UK.) by placing the
opened PCL at the inlet and outlet of the chamber.

CO2 exchange: Sixty four trees were chosen for WPP measurements
which consisted of two trees from each control treatment and three trees from
each of the remaining treatments from each variety and from the barrier and non-
barrier plot. CO2 exchange measurements were determined for each tree at
seven dates throughout the 1997 growing season. The first measurement was at
petal fall (6/8/97), the second at fruit diameters 18-22 mm (6/28/97), and the third
through the seventh measurements were determined at full canopy development
(7/9, 7/25, 8/6, 8/30 and 9/16/97, respectively). The sample air and reference air
were sampled three times for each tree at approximately 15 min intervals and
averaged. We allowed about five minutes to pass before taking measurements
on each tree to ensure that all of the air from the last tree had flushed through the
system. The PAR, relative humidity and temperature were taken at every third
measurement or more frequently on partially cloudy days.

Entomology Measurements

On July 22, August 28 and October 15, 1997 entomologists from the
Department of Entomology at Michigan State University evaluated damage
caused by insects on each of the experimental trees. The number of mines from

the Spotted Tentiforrn Leafminer, Phyllonorycter spp., was determined by a one

29

minute visual search of the canopy. The amount of feeding from Lepidoptera,
mainly Oblique-Banded Leafroller, Chon’stoneura rosaceana (Harris), was
determined by a one-minute search of the shoots. To determine the amount of
damage caused by Rosy Apple Aphids, Dysaphl's plantaginea (Passen'ni), a one-
minute visual inspection of the shoots was performed. Aphid damage was
identified on emerging shoots as well as by the incidence of stunted leaves,
cupped leaves and deformed shoot growth. The amount of bronzing and burning
caused by European Red mite, Panonychus uImi (Koch), and white apple
leafhopper, Typhlocyba poman'a (McAtree), was ranked on a scale of 1-5
depending on severity with one being least severe and five being the most
severe.
Yield

Fruit was harvested on September 24-26, 1997 and kept separate by tree.
The fruit was separated into categories by weight (>270, 215-270, 170-215, 130-
170, 95-130 and <959), and the number and weight of mm in each category were
recorded.
Damage thresholds

WPP was correlated with the damage assessments and yield. The
damage assessments for individual pests were added to get total foliar damage.
This total foliar damage was then graphed against WPP. Individual pest
numbers were also graphed against WPP. The final measurement of WPP

(9/16/97) was correlated with the average yield per tree.

30

1999 Experiment
Plant Material

The experiment included 30 one-year-old ‘Empire’lM26 apple trees. The
trees were planted on April 22, 1999 in three-gallon pots with sterilized sandy
loam soil from the greenhouse of Michigan State University. The trees were
headed back to two lateral shoots per tree at the time of planting and transported
to the Horticultural Teaching and Research Center where they were placed on a
gravel pad approximately 2 m apart. The plants were kept well watered and
each tree was fertilized with 4.5 gm of 20N:20P:20K at two weeks intervals.
Pesticide Treatments

Treatments were arranged in a completely randomized design with three
treatments: 1) a control in which no pesticides were sprayed; 2) a soft IPM
treatment with four sprays applied at weekly intervals of the fungicides Elite®
45DF at 0.2 mill and Dithane® F45 at 1.3 mI/l followed by one spray of the
insecticides SpintorTM 25C at 0.2 mill and Provado® 1.6F at 0.2 mill; 3) a
conventional treatment with four weekly sprays of the fungicide Dithane followed
by one spray of the insecticides Lannate“ 9OSP at 0.6 mill and LorsbanTM 4EC at
0.6 mlll. There were ten replicates of each treatment for a total of 30 trees.
Whole Plant Measurements

Following the last application of pesticides, whole tree CO2 exchange was
estimated. The design for measuring WPP was the same as described earlier for
the 1997 experiment except that the chamber had a smaller volume and the

wood base had a smaller diameter. The number of air exchanges per minute

31

was approximately 2.5. The gas exchange system used was the ClRAS-1 (P.P.
Systems, Haverhill, MA). The air flow through the system was measured by the
time required to fill a polyethylene bag of known volume with the air exiting from
the outlet of the chamber as described by Giuliani et al. (1997b). In addition to
WPP, single leaf photosynthesis was measured using the ClRAS-1 with the leaf
chamber attached. The incident PAR and temperature were measured using the

same procedures as in 1997.

32

RESULTS

1997 Field Experiments.

Rate of photosynthesis declined as the season progressed from a
maximum of 1-5 pmol CO2-cm'2 TCSA-s’1 to a minimum of < 0.5 pmol CO2-cm‘2
TCSA-s'1 for the barrier and non-barrier plots, for both varieties ‘Empire‘ and
‘Liberty’ and all treatments (Fig. 4 and 5). Environmental conditions on the dates
that WPP was measured are given in Table 2.

EarIy in the season, there were greater differences between treatments
than later in the season. In particular, for the first measurement period at petal
fall, the two soft IPM treatments had higher rates of photosynthesis than the
conventional IPM treatments and the control trees on the non-barrier plot
‘Empire’ and ‘Liberty’ (significant at p 5 0.10), but was not significant for the
barrier plot ‘Empire’ and ‘Liberty’ (Fig 4).

Total foliar damage due to insect feeding was estimated using the
following formula: Total Damage index = number of mines + amount of feeding
by lepidoptera + amount of damage causes by aphids + the amount of bronzing
and burning. The non-barrier plot had more total foliar damage than the barrier
plot in July, August and October (significant at p 5 0.05) (Fig 6).

WPP decreased with increasing foliar damage (Fig. 7). Total foliar
damage was found to be correlated with WPP on ‘Empire’ (Table 3) in July
(significant at p 5 0.10), August (significant at p 5 0.05) and October (significant
at p 5 0.05) for non-barrier plot. Also, total foliar damage was correlated with

WPP In August on ‘Liberty’ and ‘Empire’ (significant at p 5 0.10) for both the
33

5.0 -
4.5 -
4.0 <
3.5 <
3.0 1
2.5 <
2.0 ~
1.5 -

WPP (pmol COz-cm'z-s")

1.0 .
0.5 -

0.0 J
5.0 -

4.5 4
4.0 <
3.5 -
3.0 -
2.5 1
2.0 1
1.5 <
1.0 -
0.5 -
0.0

WPP (pmol coz-cm'2-s")

 

Non-Barrier 'Empire'

 
  
  
  
  
  
  

 

—o— Ent. Control

~D- kin. Control

+ Soft PM +Fluazinam
—x— Soft PM -Fluazinam
+ Oonv. PM - Fluaz'nam
-o— Conv. PM + Fluazinam‘

 

 

 

Non-Barrier 'leerty'

 

 

5/30

Alt Temperature (‘C)

6/19 7/9 7/29 8/1 8 977 9/27
Date In 1997

—o— Mnirrum A'r Term.
—0— thxirmm Ai' Terrp.

     

 

09-Jun 29-Jun 19—Jul 08-Aug 28-Aug 17-Sep 07-Oct
Date In 1997

Figure 4. Whole plant photosynthesis per cm2 TCSA measured during the 1997
growing season for non-barrier plot varieties ‘Empire' and ‘Liberty'. Vertical bars
indicate standard error.

34

.‘I
o

   
  
  
  
  
  

 

 

 

 

 

 

 

Barrier plot 'Emplre'
6.0
—o— Ent. Control
'79 5 0 —u—Path. (bntrol
”g + Soft PM + Fluazinam
0 + Conv. PM - Fluazinam
g 3.0 —O— Conv. PM + Fluazinam
5
a.
l 2.0
3
1.0 «
0.0 -
Barrier Plot 'leerty'
6.0 ~
.3“ 5.0 -
I."
q
5 4.0 -
2 3.0 -
o
E
5 2.0 -
1;
o.
3 1.0 -
0.0 . . . f . .
5/30 6/19 7/9 7/29 8/18 9/7 9/27

Date In 1997

Figure 4 Continued. Barrier plot varieties ‘Empire' and ‘Liberty’.

35

20 . +BILQJnt.
*’ Non-Barrier 'Enplre'

13 . —D— Path.Cont.

—)(—SoftFM-Flu.

.5
&

 

WPP (pmol COz'm'zs")

 

 

Non-Barrier 'leerty'

16‘

 

WPP (p mol COrm'z-s")

 

 

6/8 6/22 7/6 7/20 8I3 8/17 8/31 9/14
Dates In 1997

Figure 5. Whole plant photosynthesis per rn2 leaf area measured during the
1997 growing season for non-barrier plot varieties ‘Empire’ and ‘Liberty’. Vertical
bars indicate standard error.

36

l I
25.0 - Barrier Enplre

 

 

 

 

 

—o—Ent.Cont.
—o—Path.(:ont.
+ 1 FM- .
.5200 s°t H"
- +Soft PM-Flu.
”E +Conv.FMFlu.
6 15.0 ‘ —o—Conv.FM+FIu.
0 I
'0
E 10.0 4
3
n.
l h
3 5.01
0.0 J
25.0 - .
Barrier Liberty
‘5‘ 20.0
'1.»
q. _
.E
N 15.0 4
O
0
g 10.0 1
3
n.
E 5.-
0.0 - . , - , . “5 a?
6/8 6/22 7/6 7120 8/3 8/17 8I31 9114

Dates in 1997

Figure 5 Continued. Barrier plot ‘Empire’ and ‘Liberty’.

37

Table 2. Dates that whole plant photosynthesis was measured and the environmental

conditions on those dates.

weather station data

 

 

 

 

 

 

 

 

Growth Air Temperature Light Alr Temp. Total solar
Stage Date mln.- max. 1°C) Conditions Max. Rad. (lylday)

Petal Fall 04-Jun 23-32 sunny 24.8 651.5
06-Jun 24-31 sunny 23.4 321 .2
09-Jun 20-31 sunny 28.4 662.2
10-Jun 25-33 sunny 33.2 681.4
11-Jun 22-32 sunny 30.1 514.2
12-Jun 23-28 sunny 24.8 562.3
13-Jun 24-33 partly cloudy 28.7 570.3
Fruit size 23-Jun 25-37 sunny 30.9 513.3
1 8-22mm 24-Jun 35-43 sunny 32.2 650.2
25—Jun 30-35 sunny 28.3 620.3
27-Jun 31-40 partly cloudy 29.2 724.7
01-Jul 25-39 partly cloudy 29.1 518.9

Full Canopy 07-Jul 20-26 sunny 24.1 696
08-Jul 20-24 sunny 23.2 205.1
10-Jul 19-28 sunny 25.8 722.6
1 1-Jul 20-36 sunny 27.7 689.8
14-Jul 28-39 sunny 34.3 450.3
Full Canopy 22-Jul 19-26 sunny 25.7 462.2
24-Jul 23-42 partly cloudy 29.4 470.9

25-Jul 25-32 sunny 28.9 482

28-Jul 25-32 sunny 31 .1 647
Full Canopy 04-Aug 21-29 sunny 27.9 604.5
05-Aug 18-24 sunny 24.8 651.6
06-Aug 20-26 partly cloudy 25.9 476.9

07-Agg 21-31 sunny 26.6 635

Full Canopy 26-Aug 26-27 sunny 24.8 415
27-Aug 25-31 sunny 28.9 530.5

28-Aug 20-23 partly cloudy 21.6 321.1
29-Aug 18-24 partly cloudy 24.1 301 .7
03-Sep 16-21 sunny 21.4 569.9
Full Canopy 08-Sep 16-22 partly cloudy 20.5 361.2
18-Sep 21-29 sunny 26.8 457.2

19-Sep 16-20 sunny 25.4 62.4
23-Sep 15—21 partly cloudy 20.9 387.8

 

38

Non-Barrier ‘Emplre‘ Non-Barrier Plot 'leerty'

 

 

 

 

 

140. 1401
x ‘.
81201 1201 IJuIy
5 DAugust
3100. 100i
a
E 80.1 801
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5 60. 601
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60.
5
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310-
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I'- ‘3‘ i; 1 I1“. '0' i';
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at 22“ .5 39¢ 1* 3y
Treatments Treatments

Figure 6. Total foliar damage for three dates in 1997 determined by the addition
of individual damages from mines, Iepidoptera, aphids and bronzing and burning.

39

Non-Barrier PM 'Emplre‘ Non-Barrier plot 'leerty'

 

 

 

 

 

 

 

 

1.6l 1.6 1
1.4 - 1.4 -
3': o.luly1997
as 1.21 Q . 1'21 uAugust1997
.0 1.0 ~ . 1.0. :. AOctobor1997
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Barrier plot 'Emplre' Barrier Plot 'leerty‘
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1.4 ‘ 9 1_4 L O
‘1'“ O O
1' 1'2 I .0. 1'2 ‘ oJuly1997
g 1.0 ~ .. 1.0 . o. e oAugust1997
Octobe 1997
3 0-8 ‘ . t 0.8 - “z o ‘ r
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0 20 40 60 80 0 20 40 60 80

Total Foliar Damage Total Foliar Damage

Figure 7. Foliar damage Vs whole plant photosynthesis for non-barrier and
barrier plots varieties ‘Empire’ and ‘Liberty’.

40

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barrier and non-barrier plots. Damage caused by tentiform leafminer was found
to be correlated with WPP in July (significant at p _<_ 0.10), August (significant at p
_<_ 0.05), and October (significant at p _<_ 0.05) for non-barrier ‘Empire’ and in
August (significant at p 5 0.10) only for non-barrier ‘Liberty’ and barrier ‘Empire’
varieties. Damage caused by lepidoptera was found to be correlated with WPP
in July and August (significant at p 5 0.10) for non-barrier ‘Empire’ and in October
(significant at p < 0.10) for non-barrier ‘Liberty’. Foliar damage caused by aphids
was found to be correlated with WPP in October (significant at p _<_ 0.10) for
barrier ‘Liberty’. Bronzing and burning damage was correlated with WPP in
October (significant at p _<_ 0.10) for non-barrier “Empire”, July (significant at p 5
0.10) for non-barrier ‘Liberty’, and July and October (significant at p 5 0.10) for
barrier ’Liberty’.

Average yield was greater in the barrier plot than the non-barrier plot (0.86
and 0.79 kg-cm'2 TCSA respectively) (significant p _<_ 0.10). Average yield for
‘Empire’ was higher than ’Liberty’ (0.86 and 0.79 kg-cm'2 TCSA respectively)
(significant p _<_ 0.10) (Table 4). Average fruit size was greater in the non-barrier
plot than the barrier plot for both ‘Empire’ and ‘Liberty’ (Fig. 8). There were no
yield differences between treatments. No significant correlation was found
between total weight of fruit per tree and WPP (Fig. 9). A correlation was
observed between total foliar damage and yield for the barrier ‘Empire’ in July,

August and October (significant p 5 0.10).

42

Table 4. a)Average yield per TCSA and % fruit > 1309 for barrier and
non-barrier plot and 'Empire' and 'Liberty'. b) Average yield per tree and
% fruit > 1309 for apple IPM plots, CHES, 1997.

 

 

 

 

 

 

 

 

 

 

 

a) Average Yield (kg) % Fruit
per cm2 TCSA > 130g
Plot
Barrier 0.86 39
Non-barrier 0.79 63
Variety
Empire' 0.86 46
Liberty' 0.79 56
b) Average tree yield (kg) % Fruit
Barrierngot 'Emplre' per cm2 TCSA > 130g
Ent. Control 0.24 32
Path. Control 0.68 32
Soft lPM+Flu. 0.98 25
Soft IPM-Flu. 1.26 23
Conv. IPM-Flu. 0.68 29
Conv. IPM+Flu. 0.76 42
Barrier plot 'Liberty'
Ent. Control 1.06 34
Path. Control 0.80 54
Soft IPM+F|u. 0.90 63
Soft IPM-Flu. 0.88 34
Conv. IPM-Flu. 0.87 41
Conv. lPM+FIu. 0.95 55
Non-barrier plot 'Emplre'
Ent. Control 0.91 52
Path. Control 0.85 57
Soft IPM-I-Flu. 0.94 68
Soft IPM-Flu. 0.98 61
Conv. IPM-Flu. 0.89 58
Conv. |PM+Flu. 0.89 79
Non-barrierplot ’Libfl
Ent. Control 0.66 50
Path. Control 0.63 74
Soft IPM+Flu. 0.78 70
Soft lPM-Flu. 0.87 38
Conv. IPM-Flu. 0.53 76
Conv. IPM+FIu. 0.57 76

43

 

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Non-barrier 'Emplre'

I Ent. Oont. Avg. %>1309
D Path. Cont 62%

I Soft FM+Flu.

a Soft FMFlu.

Conv. FM-Flu.

BCbnv. FM-l-Fh.

 
 
  

   

  

 

  

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270 215 17° 130 270 215 170 130
Barrier ‘Emplre' %>1309 Barrier ‘Liberty’
5 ~ %>1309 Avg. %>1aog 5 ~ 34 Avg, %>1309
32 I Ent. Cont 30% ' B‘Lcm'" 47%
54
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g“ 25 .Sdtmm : 63 ISonmnu. <
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>270 215- 17 130' 95' ‘95 >270 215- 170- 130- 95- 30 Q5
270 215 170 130 270 215 170

Fruit Size (9) Fruit Size (9)

 

 

 

 

Figure 8. Fruit size Vs average yield per tree for non-barrier and barrier plots
varieties ‘Empire’ and ‘Liberty’ for 1997.

Nod. :35 5.8:. can .985. 8:25,
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45

1999 Potted Plant Experiment.

WPP of the soft IPM treatment (Elite®, Dithane® Provado® and Spintor®)
were found to be slightly greater than the conventional IPM treatment (Dithane®,
Lorsban® and Lannate®) and the control (no pesticides) on all three dates of
measurement (Table 5). In addition, we found that the soft IPM treatment had
higher rates of single leaf photosynthesis than the conventional IPM and the
control for the first, second, and fourth dates of measurement (June 17, June 21
and July 12, 1999 respectively) (Table 5). On the third date (June 28, 1999), the
single leaf photosynthesis of the conventional IPM treatment was greater than
the soft IPM and control treatments. Measurements of average shoot number

and length showed no differences between treatments (Table 5).

46

Table 5 a) Whole plant photosynthesis for potted apple trees.
b) Single leaf photosynthesis for potted apple trees. c) Shoot
number and average shoot length for potted apple trees.
Means for each date followed by the same letter are not
significantly different (Duncan’s test p 5 0.10).

 

 

 

 

 

a) Average WPP
Treatment Date umol COz-cm’Z-s'1
17-Jun
Control 0.39 a
Conv. IPM 0.51 ab
Soft IPM 0.55 b
18-Jun
Control 0.42 a
Conv. IPM 0.62 a
Soft IPM 0.55 a
25-Jun
Control 0.60 a
Conv. IPM 0.71 ab
Soft IPM 0.80 b
b) Single leaf Pn
Treatment Date umol COz-m'z-s'1
1 7-Jun
Control 6.68 a
Conv. IPM 6.28 ab
Soft IPM 7.74 b
21 -Jun
Control 5.66 a
Conv. IPM 7.05 b
Soft IPM 8.70 c
28-Jun
Control 8.52 a
Conv. IPM 10.84 a
Soft IPM 10.24 b
12-Jul
Control 8.14 a
Conv. IPM 7.83 a
Soft IPM 8.17 a
c) Average Avg. Shoot Length
Treatment Shoot number per tree (cm)
Control 14.3a 32.72a
Conv. IPM 14.63 32.69a
Soft IPM 13.8a 30.89a

47

Discussion

In our research we attempted to develop a damage threshold for foliar
pests in apple though the use of WPP. A correlation was found for total foliar
damage and WPP in the non-barrier plot for all three assessment dates in
‘Empire’ and August only in ‘Liberty’. The correlation between WPP and damage
could be interpreted that a damage threshold was reached in the non-barrier plot,
where there was greater foliar damage, whereas, in the barrier plot, where there
was much less damage, no threshold was reached. We observed more
correlations between WPP and total foliar damage for ‘Empire’ than ‘Liberty’.
‘Liberty’ was developed as a disease resistant variety, which in experiments has
produced excellent quality fruit with no fungicide sprays (Ellis, et al., 1994).
Possibly ‘Liberty’ is more resistant to insect feeding than ‘Empire’ as well.

Damage caused by tentiform leafminer was also found to be correlated
with WPP for non-barrier ‘Empire’ on all three assessment dates and in August
for non-barrier ‘Liberty’. This was the only individual insect damage that was
correlated to WPP. Possibly damage done by leafminer is much more influential
in reducing WPP than the other individual pests. Kappel et al. (1987) reported
increased ethylene levels of leaves damages by spotted tentiform leafminer
which can lead to premature fruit and leaf drop.

Yield was not found to be correlated with WPP. This is not an uncommon
result as reduction in photosynthetic capacity does not always culminate in
reduced yield. Results of studies have varied considerably, probably due to

differences in the environment, the timing and severity of the damage and the

48

physiological status of the tree, especially crop load (Francesconi et al., 1996a).
Yield was greater in the barrier plot than the non-barrier plot. Possibly due to the
reduced amount of foliar damage that the barrier plots experienced. The non-
barrier trees could have had reductions in production of photosynthates caused
by reduction in leaf area by insect feeding. One reason for this difference could
be because of the barrier surrounding the plot. There was less wind movement
within the barrier plot which may have reduced some damage to the trees and
crop and reduced water loss (Solomon, 1981). The yield in the non-barrier plot
may also have been reduced by the foliar damage that occurred. Disegna (1994)
showed that inhibition of photosynthesis at 15 and 30 DAFB reduced the yield
indicating that timing of damage is very important. Lakso et al. (1998)
demonstrated that just after bloom and just before harvest are two periods where
damage to leaf area could affect yield. These are two periods when
carbohydrates could be limiting.

We observed a decline in photosynthesis as the season progressed.
There are many variables that can affect photosynthesis. In general leaf
photosynthesis peaks just before the leaf reaches full expansion, remains steady
for some time, then decreases (Flore and Lakso, 1989). The rate of decline can
be slowed with the presence of fruit (Downtown et al., 1987), by debudding
(Satoh et al. 1977) or by summer pruning (Rom and Ferree, 1985). For example
seasonal effects have been shown for apple where maximum assimilation rates
were observed in late June when leaves reached full expansion then declined to

a minimum at the end of July (Ghosh, 1973). Cherry leaves were shown to reach

49

their maximum rate of photosynthesis at 80% leaf expansion and remain at a
maximum level for 2-4 weeks before declining (Sams and Flore, 1982).

Another important factor in photosynthesis is light intensity, but likely it
was not a factor for the decline in photosynthesis as the season progressed
because all the measurements were determined under saturating light intensities,
which for apple are 400-600 ,ttts-m'z-s‘1 for individual apple leaves (Faust, 1989).

Air temperature is another possible factor for the decline in WPP over the
season. High air temperatures can increase respiration rates and cause an
apparent drop in the rate of photosynthesis (Heinicke and Childers, 1937). The
air temperature for optimum photosynthetic rate of apple leaves is between 20
and 30°C above which photosynthesis declines (Lakso and Seeley, 1978). For
potted plants this temperature is even lower. Apple leaves showed decreases in
photosynthesis above 20°C and appeared to be very sensitive to increases in
vapor pressure deficit compared to other species (Higgins et al., 1992). More
recent studies on whole plants have demonstrated small decreases in
photosynthesis above 15°C, and drastic declines above 25°C indicating that the
optimum temperature for WPP is much lower than previously thought
(Francesconi et al., 1998). Stomata are involved in the regulation of C02
exchange and water vapor diffusion. Transpiration is induced by evaporative
demand and is driven by temperature and humidity. In the case of high
temperature and low relative humidity large differences in water vapor
concentrations between the leaf surface and the air can occur and cause closure

of stomata.

50

Crop load can have an effect on the rate of photosynthesis as well. While
it appears that crop load affects the vegetative-reproductive ratio, its effect on
photosynthesis is not well known. Giuliani et al. (1997a) observed differences in
photosynthesis with fruiting and non-fruiting trees, but did not detect a difference
between crop loads. Another study with apple showed that after canopy
development, there are higher rates of photosynthesis in fruiting trees than non-
fruiting trees during the period of rapid increase in fruit growth (Fujii and
Kennedy, 1985). Ghosh (1973) found that towards the end of the vegetative
period the leaves of fruit-bearing shoots showed a slightly higher rate of
photosynthesis, whereas, leaves of shoots without fruits showed a reverse trend.
The time of photosynthesis measurement is important with relation to crop load.
In grape vines, during the period of rapid sugar accumulation by the fruit,
photosynthesis of plants with and without fruit were similar early in the day, but
declined earlier in the day for the non-fruiting vine. The difference in
photosynthesis between the fruiting and non-fruiting vines may have resulted
from carbohydrates building up faster in the non-fruiting vine resulting in
feedback inhibition (Downton et al., 1987). In orchard studies, Kennedy and Fuji
(1986) observed two periods during the growing season when the rate of
photosynthesis in leaves of fruiting spurs was 10-20% higher than the leaves on
non-fruiting spurs. The first period was during flowering, and the second during
fruit maturation. For 2-4 weeks after bloom, fruits are supported mainly by
carbohydrates from spur leaves and growing shoots receive most of their

carbohydrates from extension leaves on the shoot (Lakso et al., 1997). During

51

this 2-4 week period, and just before harvest appear to be two periods during the
growing season that are possible potentials for carbon limitation for apple fruit
growth (Lakso et al., 1998). Meaning that damage occurring in these periods
could have more of an impact on yield than other periods. If crop load is high
there will be more of an effect than if crop load is light (Francesconi et al.,
1996b).

Injury to the leaf caused by diseases or insects, as well as defoliation, has
the potential to decrease photosynthesis rate and cause economic loss.
Outbreaks of mites in an orchard can reduce the rate of photosynthesis
significantly. Ferree et al. (1986) found that as the population of two-spotted
spider mites (Tetranychus urticae) increased, photosynthesis decreased and the
reductions appeared to permanently destroy the photosynthetic capacity of the
leaf. A population of 60 mites per leaf caused a significant reduction in apple
photosynthesis three days after placement on the leaf. Nine days after infection,
15 mites per leaf reduced photosynthesis by 26%, 30 mites per leaf by 30%, and
60 mites per leaf by 43% below the value observed in uninfected controls. Foliar
damage causes reductions in the ability of leaves to make sugars by
photosynthesis. This reduces the amount of carbohydrates that are translocated
to the fruit which can cause reductions in fruit size and quality. Damage caused
by European red mite can cause fruit growth reductions earlier and more severe
on normally cropped trees than on lightly cropped trees (Francesconi et al.,

1996b). In a previous study Lakso et al. (1996) introduced the term mite days

52

which are the previous number of mites per leaf added to the current number of
mites per leaf and multiplied by the number of days between samples.

The reductions in WPP that we saw throughout the season could be due
to any one or a combination of the factors above. The trees in the non-barrier
plot had a lower rates of WPP than those in the barrier plot. There was also
more damage in the non-barrier plot than the barrier plot both by insects and
possibly by other factors such as diseases and wind. The yield in the non-barrier
plot was less than that of the barrier plot suggesting that there could be an effect
from the increased damage experienced in the non-barrier plot, even though
yield was not found to be correlated with WPP.

Early in the season, there were greater differences between treatments
than later in the season. In particular, at the beginning of the season, the two
soft IPM treatments had higher rates of photosynthesis than the conventional
lPM treatments and the control trees. This was the case for both the non-barrier
and barrier plots and both varieties ‘Empire’ and ‘Liberty’. We repeated this
experiment on potted plants in 1999 and found results to be consistent with the
1997 field study. One explanation for the increase in photosynthesis that the soft
lPM treatments showed could be due to the pesticides themselves. The two
insecticides used were Provado‘b and Spinosad®. Provado" is an insecticide
used at petal fall to prevent leafrniners, rosy apple aphids, and leafhopper. It’s
active ingredient is imidacloprid which is a systemic, chloro-nicotinyl insecticide.
It works by interfering with the transmission of stimuli in the insect’s nervous

system. Specifically it causes a blockage in a type of neuronal pathway that is

53

more abundant in insects than warm-blooded animals. This blockage leads to
accumulation of acetyl choline, an important neural transmitter, resulting in the
insect’s paralysis and eventual death (The pesticide management education
program, 1999). Spintor‘D controls lepidoptera larvae, leafminers and thn'ps. It is
a fermentation product derived from tetracyclic macrolide produced by the
actinomycete, Saccharopolyspora spinosa and consists of two structurally related
compounds, namely spinosyn A and spinosyn D which provide the insect control
activity. In addition to the two pesticides used, two fungicides were applied
namely Dithane“ and Elite®. Dithane® is a broad-spectrum, fungicide. It’s active
ingredient is Mancozeb which belongs to the chemical family ethylene
bisdithiocarbamates (EBCDs). It controls fabrea leaf spot, rusts and scab (The
pesticide management education program, 1999). Elite® controls powdery
mildew and leaf spot. Its active ingredient is Tebuconazole which is a sterol
demethylation inhibitor (DMI) fungicide. It is systemic and provides control by
preventing completion of the infection process. It is rapidly absorbed by plants
and is translocated in young growing tissues (The pesticide management
education program, 1999).

Because some of these chemicals have effects on metabolic pathways in
insects, perhaps these chemicals may cause metabolic changes in plants as
well. In addition, there have been studies showing that pesticides with different
modes of action can have synergistic effects which can be either positive or
negative. Samoucha and Gisi (1986) found that mancozeb mixed with metalaxyl

provided better control of downy mildew than either of the chemicals alone. In a

study with tebuconazole (the active ingredient in Elite®), rape was found to have
higher yields with the use of tebuconazole as compared with two other fungicides
(Kaspers and Siebert, 1989). Catrso et al. (1997) also found tubuconazole to
have an effect other than its fungicide properties. They found that it increased
the number of sprouts established in citrus. There is some evidence pointing to
seasonal variation in spray retention by leaves of apple (Hall et al., 1997). Spray
retention was found to correlate positively with root hair density. This could
potentially be a reason for the positive effect of the pesticides on WPP that we
observed at the beginning of the season. Young leaves have many more

trichomes than older leaves and, therefore, retain the spray longer.

55

Summary and Conclusions

The use of WPP as a possible tool to determine damage thresholds has
been demonstrated. If carbohydrate supply and demand is the mechanism by
which various foliar feeders affect apple tree productivity, then we can attempt to
understand the amount of damage that can occur before the need for some type
of action. This is especially helpful with our knowledge of times during the
growing season that are particularly sensitive to decreases in photosynthesis and
the interaction with crop load.

Although our results in general support our hypothesis and are promising,
further research should extend to different damage levels to more fully define the

interactions between WPP and damage.

56

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