• TABLE OF CONTENTS
HIDE
 Front Cover
 Title Page
 Table of Contents
 Introduction
 Materials and methods
 Results
 Discussion
 Conclusion
 Reference














Title: Effect of manual defoliation on unstaked fresh-market tomato yield and quality
CITATION DOWNLOADS THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00026837/00001
 Material Information
Title: Effect of manual defoliation on unstaked fresh-market tomato yield and quality
Physical Description: Book
Creator: Keularts, Jozef Leo Willem
Publisher: Agricultural Experiment Stations, Institute of Food and Agricultural Sciences, University of Florida
Publication Date: 1985
Copyright Date: 1985
 Record Information
Bibliographic ID: UF00026837
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: adb3801 - LTUF
14198281 - OCLC
000585169 - AlephBibNum

Downloads
Table of Contents
    Front Cover
        Front Cover
    Title Page
        Title Page
    Table of Contents
        Table of Contents
    Introduction
        Page 1
    Materials and methods
        Page 2
        Page 3
        Page 4
    Results
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
    Discussion
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
    Conclusion
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
    Reference
        Page 39
        Page 40
        Page 41
Full Text

June 1985 Bulletin 847 (technical
1 / 7

9117




Effect of Manual Defoliation on Tomato
Yield and Quality


Jozef Keularts, Van Waddill and Ken Pohronezny





4-














r--t









Agricultural Experiment Stations
Institute of Food and Agricultural Sciences
University of Florida, Gainesville
















Effect of Manual Defoliation on Unstaked
Fresh-Market Tomato Yield and Quality

Jozef Keularts, Van Waddill and Ken Pohronezny






















Jozef Keularts was formerly a graduate research assistant, Van
Waddill is Center Director, Everglades Research and Education
Center, Belle Glade and Ken Pohronezny is an Associate Professor
of Plant Pathology at the Tropical Research and Education Center,
Homestead, IFAS, University of Florida.












CONTENTS

Introduction ........................................... 1
Materials and Methods ................................ 2
General ........... .. .... .... .......... ........... 2
One-time Defoliation ............................... 3
Experiment 1: spring crop 1978 ....................... 4
Experiment 2: fall crop 1978 .......................... 4
Experiment 3: spring crop 1979 ....................... 4
Repeated Defoliation ................................ 5
Experiment 4 ............. ........................ 5
Experiment 5 ...................................... 5
Results..................... ..... ........ ......... 5
Experiment 1 ...................................... 5
Experiment 2 ..................................... 7
Experiment 3 ......................................10
Experiment 4 ............... ........ ............. 12
Experiment 5 ..................................... .13
Discussion .............. ........................... 28
Conclusion ........................................ 34
References Cited ..................................... 39








INTRODUCTION

Several of the important tomato pests are foliage feeders although
many of them inflict damage directly to the fruit as well. Reduction
of marketable yield is, therefore, not solely related to the amount
of foliage consumed but includes yield reduction due to damaged
fruit. Damage by leafminers, Liriomyza spp., in contrast, is
restricted to the leaves and the injury is different from that caused
by most foliage feeders. Only the leaf mesophyll is consumed, leav-
ing both upper and lower epidermis intact. The presence of a large
number of leafminer larvae within one leaf may result in leaf death
and subsequent abscission. In addition, yellowing and necrosis of the
leaf tissues around the mines may occur, even if the larval popula-
tion is small, again sometimes resulting in abscission of the entire
leaf. Partial or even complete defoliation of tomato plants may result
from the combined effects of direct leafmining and subsequent leaf
abscission.
In recent years, the population of leafminers has become so large
that growers consider these insects their most serious pests (25).
Because of the clearly visible damage inflicted on tomato plants, a
negative effect on the yield is often suspected. However, it has been
shown repeatedly that consumption of leaves and other plant tissues
by insects does not necessarily reduce plant vigor (reproductive
capacity) (7). In fact, Harris (8) suggested that sometimes a certain
density of "pest" insects may be required for a crop to attain its
maximum yield. Potato yield increase following partial defoliation
has been demonstrated (30). Despite many attempts to find a cor-
relation between leafminer damage and tomato yield, no consistent
results have been obtained. Most reports have found no significant
effect of naturally occurring leafminer populations and insecticide-
induced populations on tomato yield (11, 12, 15, 28). However, in
some fields and in some years yield reduction was found (29, 35).
The greatest damage by leafminers is often considered to be im-
posed on seedlings or young plants which, as a result of weakening,
may die or become stunted (2, 5, 16). Severe damage by leafminers
to cantaloupe, resulting in complete crop loss (9), and to honeydew
melon, resulting in reduction in yield and fruit quality (20), has been
reported.
Defoliation by means other than insect injury has also been found
to have varying effects on fruit production in tomato. The various
levels of defoliation resulting from varying degrees of early blight
control with fungicides, appeared not to be correlated with tomato
yield (26). Defoliation by a bacterium (Xanthomonas campestris pv
vesicatoria (Doidge) Dye) resulted in significant reduction in fruit

1








size (23). One commercial variety of tomato could withstand con-
siderable foliage damage due to ozone exposure for a long period
of time (21) without significant reduction in fruit size, weight or
number, even though the fresh weight of stems and leaves was
lowered by 27%. Even a decrease in stem and leaf fresh weight of
62% seemed to have minimal effects on yield.
Mechanical defoliation of tomato plants to study its effect on yield
has been performed several times. Wiebe (33) found a significant
yield reduction in greenhouse tomatoes, when all except the top two
feet of leaves were removed, when compared to plants with only
the senescent leaves taken off. Selective removal of overlapping
leaves had no effect on yield. A yield reduction, especially in the
largest fruit size categories was found as a result of repeated defolia-
tion at high levels (60% or more) in staked tomato plants (13). Defolia-
tion (80%) of processing tomatoes in Ohio when the tomatoes were
at first bloom, full bloom, or 2.5 cm fruit diameter resulted in reduced
yield (36). On the same study, defoliation of 25% or 50% prior to
or at full bloom did not influence yield; however, 25% or 50% defolia-
tion when fruits were 2.5 cm diameter did decrease yield (36). The
effects of mechanical defoliation on yield and fruit quality of unstak-
ed tomatoes grown for the fresh market have not previously been
studied.
Actual damage to tomato plants by the leafminer-disease complex
occurs gradually, sometimes over a considerable period of time. Ex-
act duplication of this damage is virtually impossible so that simula-
tion by mechanical defoliation may not accurately mimic the effect
of natural defoliation (4). However, interpretation of this damage
may be enhanced by using Pena's description of tomato phenology
(22). He defined three developmental stages for 'Flora-Dade':
vegetative (1 to 35 days), reproductive (36 to 135 days), and senes-
cent (136 to 200 days).
The study presented here was undertaken to determine: 1) the
times at which unstaked tomato plants are most sensitive to defolia-
tion, and 2) the damage threshold at which unstaked tomato plants
will show significant loss in yield and fruit quality when (a) defoliated
only once, and (b) defoliated repeatedly.

MATERIALS AND METHODS
General
'Walter' tomatoes were planted in 1977 and 1978 at the Universi-
ty of Florida Agricultural Research and Education Center in
Homestead, Dade County, Florida. After metribuzin was incor-
porated into the soil at a rate of 0.84 kg ai/ha, beds were prepared

2








in groups of seven with their midlines 182 cm apart. Irrigation pipes
with frost protection nozzles were set on the middle bed. The other
beds were fertilized with 7-14-14 at a rate of 2242 kg/ha placed in
two bands 30 cm apart. For the spring crop of 1978 and the spring
crop of 1979 the beds were fumigated with Dowfume MC33 at a
rate of 314 kg/ha; for the fall crop of 1978 the rate was 247 kg/ha.
Immediately after the fumigation the beds were covered with plastic
mulch with drip tubing for irrigation placed approximately 15 cm
in the soil below the plastic. Tomato seeds were planted in hills 30
cm apart in the rows. One to two weeks after emerging, the seedl-
ings were thinned to one plant per hill.
Foliage was removed by cutting the leaves off at the distal end
of the petiole with scissors. Fresh leaf weight has been consistently
found to be highly correlated to the total leaf area (25). For the one-
time defoliations, the fresh weight of the foliage removed from the
completely defoliated plants was used as a reference for removal
of the correct amount from the other plants to be defoliated.
All but the outer two plants of each plot (mature green and col-
ored fruit) were harvested three times except for the spring crop
of 1979, which was harvested only twice because of poor fruit set.
The first harvest was initiated when approximately 5% of all fruit
showed a pink color. The fruit were then graded into USDA 1 or 2
categories or classified as culls. These were then sized as extra large,
large, medium, small, and very small (18) according to the
measurements given in Table 1. The culled fruit was subdivided in-
to several categories: misshapen, blemished, sunscalded, decayed,
damaged by insects or slugs, and showing gray wall.


Table 1. Size ranges and mean weights of the size categories of 'Walter'
tomatoes.
Size Size range Mean weight
category in mm in grams
very small 48-54 67
small 54-58 99
medium 58-64 142
large 64-73 174
extra large 73 213
Source: Marlowe (1978).

One-time Defoliation
The defoliation experiments were conducted utilizing a split-plot
randomized complete-block design. Rows were assigned at random
within each of the four blocks for defoliation at a particular time.

3








Defoliation levels were assigned at random to the subplots within
each whole plot (row). Each subplot consisted of 12 plants in the
spring crop of 1978, 22 plants in the fall crop of 1978 and 17 plants
in the spring crop of 1979. Each subplot, except for the control group,
was defoliated only once, and the plants in each row in a block were
done on different dates. Defoliation levels investigated were total
(= 100%), 20%, 40%, 60%, and 80% starting from the top of the plant
(= 20% upper or 20U, 40% upper or 40U, etc.) or 20%, 40%, 60%,
and 80% starting from ground level (= 20% lower level or 20L, 40%
lower or 40L, etc.)
Yield data were analyzed and comparisons with the control were
made as a two-sided test using the Dunnett's procedure (31).
Experiment 1: spring crop 1978. The tomato seeds were planted
on November 3, 1977. Beginning November 10, 1977, pesticides were
applied twice weekly by a high volume, low concentrate boom
sprayer. The insecticide permethrin was used at alternate rates of
.056 kg ai/ha and .112 kg ai/ha. The fungicide applied simultaneously
with the insecticide was either chlorothalonil at a rate of 1.58 kg
ai/ha or mancozeb at a rate of 1.34 kg ai/ha. Form-a-Turf was ap-
plied at a rate of 7.02 1/ha when bacterial diseases threatened as
occurred during the bacterial speck epidemic of early 1978 (24).
The times of defoliation were 30 days after planting, 40 days after
planting, and so on with 10 day intervals up to and including 100
days after planting. The levels of defoliation were 100%, 80U, 80L,
60U, 60L, 40U, 40L, 20U, and 20L.
Harvesting was done between February 14, 1978, and March 23,
1978.
Experiment 2: fall crop 1978. The tomato seeds were planted
on September 13, 1978. A mixture of permethrin at a rate of .112
kg ai/ha and either chlorothalonil at 1.68 kg ai/ha or mancozeb at
1.34 kg ai/ha was applied weekly, and Form-a-Turf on demand as
in Experiment 1.
The times of defoliation were 30 days after planting, 40 days after
planting and so on with 10 day intervals up to and including 80 days
after planting. The levels of defoliation were 100%, 80U, 80L, and
60U.
Fruit was harvested between December 8, 1978, and December
28, 1978.
Experiment 3: spring crop 1979. The tomato seeds were planted
on December 28, 1978. Pesticide applications were made at the same
schedule and rates as in Experiment 2. Due to the poor stand of the
crop only a limited area of the field could be used. The number of
defoliations, therefore, had to be limited. The times of defoliation

4








were 70 days after planting, 80 days after planting, and 90 days after
planting. The levels of defoliation were 100%, 80L, 60L, and 40L.
Fruit was harvested between April 23, 1979, and May 2, 1979.

Repeated Defoliation
The defoliation experiments were conducted on the fall crop of
1978 using a randomized complete-block design. Defoliation levels
were assigned at random within each of three blocks. Plants were
defoliated at regular intervals by removing the required percentage
of the foliage present on the day of defoliation from the appropriate
part of the plants. Each plot consisted of 22 plants. One plot in each
block not mechanically defoliated served as a control.
The tomato seeds were planted on September 13, 1978. Pesticide
applications were made as described in Experiment 2.
Fruit was harvested between December 8, 1978, and December
28, 1978.
Yield data were analyzed and comparisons among treatments were
made using Duncan's New Multiple Range Test (31).
Experiment 4. Tomato plants were partially defoliated at 30, 50,
and 70 days after planting. The levels of defoliation were 60L, 40U,
40L, and 20U.
Experiment 5. Tomato plants were partially defoliated every 10
days, for the first time at 30 days after planting and for the last time
at 80 days after planting. The levels of defoliation were 40U, 40L,
and 20U.

RESULTS
Experiment 1. Defoliation from mid-season on had a striking ef-
fect on the fruit set (number of fruit on the plants at harvest) if the
defoliation levels were 60U, 80U, 80L or 100%. In nearly all of these
cases fruit set was significantly reduced to below that of the con-
trol (P 0.05). The most severe reduction was at the 100% level at
the beginning of the last third of the growing season (Table 2). Ear-
ly defoliation had no significant effect on fruit set.
Irrespective of crop phenology, the highest levels of defoliation
showed significant reduction in yield of large fruit and the combina-
tion of the two largest fruit classes in the first harvest (Table 3). The
plants were especially sensitive to leaf removal early in the first half
(30 days after planting) and early in the second half (60 to 80 days
after planting) of the season. Very few significant differences in yield
of the two largest fruit categories were found at the second harvest
(Table 4). The amount of medium-sized fruit, especially in the first
picking, was affected by defoliation at any level during the last few

5














Table 2. Influence of defoliation of 'Walter' tomato plants on fruit set.
Mean number of fruit per 10 plants
Defoliation Time of defoliation (in days after planting)
level 30 40 50 60 70 80 90 100
20% lower 437 399 437 397 378 368 392 376
20% upper 468 404 388 415 346 372 318* 413
S 40% lower 456 487 425 382 338 415 364 358
40% upper 409 396 415 344 347 358 325 334
60% lower 436 402 411 424 338 327 354 346
60% upper 463 394 320* 314* 230** 315* 338 313*
80% lower 415 409 372 278** 281** 310* 319* 328
80% upper 376 419 351 294** 268** 269** 294** 296**
100% 434 490 297** 259** 212** 225** 259** 274**
a A significant difference from the control (418 fruits) is indicated by for P<0.05 or by ** for P<0.01.
b For an explanation of the defoliation level codes see page 4.








weeks before harvesting (Table 11). Generally speaking, defoliation
earlier in the season of 60% or higher led to serious yield reduction
of medium-sized fruit in both first and second pickings (Tables 6 and
7).
Plants defoliated 30 days after planting at the three highest levels
still showed lush growth at the time of the harvest, while leaves of
the plants subjected to other treatments were senescent to varying
degrees. Analysis of variance of the fresh weight of all above-ground
parts of the plants most severely defoliated at 30, 60 and 100 days
after planting, after all fruit had been removed, showed a significant-
ly higher fresh weight for the plants defoliated early in the season
than for the plants in the control (Table 9). No significant difference
was found in any of the other times or levels of defoliation tested.
The average weight of all marketable fruit was significantly reduc-
ed only in the first harvest of the 80U and 100% defoliations 30 days
after planting. None of the treatments resulted in significant in-
creases or decreases in the weight of the culled fruit in the first two
harvests or in any particular cull category.
In many cases where defoliation significantly reduced the fruit
weight, this reduction was more noticeable in the USDA grade 1 fruit
than in the USDA grade 2 fruit, especially in the two largest fruit
categories (Table 3).
If the data from the first two harvests are combined (Tables 5 and
8) the impact of mechanical defoliation on yield can be summariz-
ed. The effect is most pronounced in the plants at first harvest.
However, increases in the second harvest tend to compensate for
the initial yield loss.
Experiment 2. Analysis of the combination of the two largest fruit
sizes (Tables 10 and 11) summarizes the differences in effects of
defoliation in the first two harvests. A reduction in the weight of
the medium-sized fruit as a result of foliage removal occurred only
in the second harvest (Tables 12 and 13). The reduction pattern was
very similar to that of the large fruit.
From combining the total yields of the first two harvests (Figure
1) it appears that the only significant reduction due to 60% defolia-
tion occurred in plants defoliated 50 days after planting.
The average weight of all marketable fruit was significantly reduc-
ed only in the first harvest by 100% defoliation of the tomato plants
50 days after planting. In the second harvest no significant reduc-
tions were found.
The weight of all culled fruit together in any of the treatments
showed no significant difference from the control in any of the
harvests. However, more sunscalded and decaying fruit were pre-
sent on plants defoliated 15 days before the first harvest at the 80%

7









I small
1500 FRUIT I medium
SIZES large
D extra large

1250


E .
S1000 **
I- *
2t **

9 750
a.





250 '
l.







0 60U 80L 80U 100 60U 80L 80U 100 60U 80L SOU 100 60U 80L 80U 100 60U 80L 80U 100 60U 80L 80U 100 DEFOLIATION LEVEL
--30---- 40------ 50--- ----60- -- -- 70---- 80----- DEFOLIATION TIME
(in days after
planting)

Figure 1. Influence of defoliation of 'Walter' tomato plants on the total yield of marketable fruit in the first two harvests
of the fall crop of 1978. A significant difference from the control (0) is indicated by for P <0.05 or by for P <0.01.
For an explanation of the defoliation level codes for all figures see page 4.










800 J USDA grade 2

700l USDA grade 1


600


1 500
0-
S400


" 300 i

I-
" 200 -







0 40L 60L 80L 100 401 60L 80L 100 40L 60L 80L 100 DEFOLIATION LEVEL
1- 70- --80------4 90------4 DEFOLIATION TIME
(in days after
planting)
Figure 2. Influence of defoliation of 'Walter' tomato plants on the mean weight of all extra large plus large fruit in the first
harvest of the spring crop of 1979. A significant difference from the control is indicated by for P<0.05 or by
"** for P<0.01.









and 100% levels. Defoliation at 80 days after planting also resulted
in more decaying fruit when 80% or more of the foliage was remov-
ed from the plants.
Experiment 3. Since only late-season defoliations could be ex-
amined for effects on yield and fruit quality, differences in reduc-
tion patterns as found in the first two experiments could not be
verified. In fact, analysis of the weight of the various fruit sizes and
total weight revealed only very few significant reductions when com-
pared to the control.
No significant differences in the weight of the extra large fruit was
detected. No extra large fruit were harvested in the second picking.
Combining the weight of all extra large and large fruit for analysis
showed a reduction by complete defoliation 70 days or 80 days after
planting (Figure 2).
The weight of all marketable fruit (Figures 3 and 4) was significant-
ly reduced by 100% defoliation at 80 or 90 days after planting.




FRUIT medium
SIZES M large
00 extra large






M 750



,

2500


II-
0 40L 60L 80L 100 40L 0OL 80L 100 40L 60L 80L 100 DEFOLIATION kEVEL
---- 7 --- ----- o----80 I 0--- DEFOLIATION TIME
(1 days after


Figure 3. Influence of defoliation of 'Walter' tomato plants on the total
yield of marketable fruit in the first harvest of the spring crop
of 1979. A significant difference from the control is indicated
by for P<0.05 or by ** for P<0.01.


10









Small
FRUIT ____
SIZES I medium

750 large





5

uS"
U.

i, *

250 -






__U-H i ^ ^ ^ i i i ^ W U -



0 40L 60L 80L 100 40L 60L 80L 100 40L 60L 80L 100 DEFOLIATION LEVEL
--- 70 ----- ---I ---- 90----- i DEFOLIATION TIME
(in days after
planting)
Figure 4. Influence of defoliation of 'Walter' tomato plants on the total yield of marketable fruit in the second harvest of
the spring crop of 1979. A significant difference from the control is indicated by for P<0.05 or by * for P<0.01.









Total weight of the culled fruit was not significantly different bet-
ween any of the treatments and the control. The weight of the cull-
ed fruit as a percentage of the total marketable fruit plus culls was
significantly higher only in the second harvest if the tomato plants
were completely defoliated 80 or 90 days after planting. Significantly
more sunscalded fruit occurred on plants defoliated 90 days after
planting at the 60% and higher levels of defoliation. Weight of the
decaying fruit was significantly greater than the control in plants
completely defoliated 70 or 90 days after planting in the first picking.
Experiment 4. When tomato plants were defoliated three times
during the growing season, the threshold for reduction in fruit weight
per plant in several size categories was lower than that found in one-
time defoliation experiments.


first harvest USDA grade 2

800 USDA grade 1

700


600 b
bc

so bc
500

S400 second harvest


300 a

5 a .
200 -


100



0 20U 40L 40U 60L 0 20U 40L 40U 60L
DEFOLIATION LEVEL

Figure 5. Influence of repeated defoliation of 'Walter' tomato plants on
the mean yield of all extra large plus large fruit (3 defoliations).
Columns not marked by the same letter represent significantly
different weights (P<0.05), Duncan's multiple range test.


12








The effect of defoliation on the yield in the two largest size
categories is summarized in Figure 5. Reduction in the weight of the
medium-sized fruit in the first picking (Figure 6) had only a minimal
effect on the total yield (Figure 7). In the second picking the increase
in the weight of medium-sized fruit and large fruit accounted for
the significant increase of the total yield.
The total yield of the first two harvests was not significantly reduc-
ed by defoliation at any level (Figure 8) while the combined weight
of all extra large and large fruit was significantly reduced only at
the 60% defoliation level.
Experiment 5. Reduction was evident in all defoliation levels
when the two largest size categories were combined for analysis
(Figure 9).
The yield of the medium-sized fruit was only significantly reduc-
ed as a result of removal of 40% of the foliage from the upper part
of the plants (Figure 10).


350 -
second harvest
| USDA grade 2

E 300 USDA grade 1

"ab
1 250 ab ab


S200

I first harvest b
150 -



ab
ab o 1
50o -



0 20U 40L 40U 60L 0 20U 40L 40U 60L

DEFOLIATION LEVEL



Figure 6. Influence of repeated defoliation of 'Walter' tomato plants on
the mean yield of all medium-sized fruit (3 defoliations).

13









In no size category was a yield reduction observed in the second
harvest.
The total yield loss as a result of repeated defoliation (Figure 11)
was mainly caused by the fewer extra large and large fruit harvested,
and although in the second harvest no significant differences were
observed, the larger fruit weight removed from the plants at that
time compensated for the lesser weight harvested in the first, since
combining the yield of the first and the second harvests showed no
significant differences (Figure 12).




first harvest
S small
900 FRUIT Imedium
SIZES o large

800 ll extra large

second harvest
700 *
a h;
Sb a
0 600 b


C
2 b a
S500 b ab ab


400 0

S 400 0 0;



200 b



00oo



0 20U 40L 40U 80L 0 20U 40L 40U 60L

DEFOLIATION LEVEL



Figure 7. Influence of repeated defoliation of 'Walter' tomato plants on
the mean total yield of all marketable fruit (3 defoliations).


14













1250 small

S FRUIT I medium
a SIZES large
Extra large


a
1000
a






0750 -














250 -














0% 20% 40% 40% 60%
upper lower upper lower

DEFOLIATION LEVEL






Figure 8. Influence of repeated defoliation of 'Walter' tomato plants on
the mean total yield of all marketable fruit in the first two
harvests (3 defoliations).


15








Table 3. Influence of defoliation of 'Walter' tomato plants on the mean yield of all extra large plus large fruit in the first har-
vest of the spring crop of 1978.
Mean yield per treatment as a percentage of the mean
yield of the controla,b
Defoliation Fruit Time of defoliation (in days after planting)
level graded 30 40 50 60 70 80 90 100
20% lower 1 96.38 101.42 99.10 114.94 125.91 110.45 20.56** 38.03*
2 144.86 100.43 81.67 90.54 63.38 108.44 74.44 87.53
1+2 118.85 100.98 91.40 104.18 98.31 109.56 44.36* 59.90
20% upper 1 84.94 101.79 73.44 96.85 86.89 113.08 47.93 33.86*
2 89.18 88.90 46.50 114.77 74.13 107.35 74.52 80.58
1+2 86.83 96.10 61.54 104.78 81.25 110.56 59.68 54.50*
40% lower 1 74.21 73.04 124.83 91.74 74.89 74.21 25.66** 57.11
2 111.06 73.86 107.54 98.55 100.90 120.83 82.85 97.69
1+2 90.49 76.85 117.21 94.77 86.40 94.80 50.92* 75.04
40% upper 1 75.66 129.56 77.30 90.35 104.73 73.65 50.93 45.30*
2 73.08 62.13 75.42 56.55 46.78 52.05 61.43 76.08
1+2 74.52 99.78 76.47 75.44 79.15 64.13 55.58 58.90
60% lower 1 86.58 75.14 97.87 106.68 17.78** 73.65 85.71 104.89
2 124.15 42.99 97.89 103.95 74.44 97.77 45.53 66.82
1+2 103.18 60.94 97.88 105.47 42.81** 84.32 67.96 88.07
60% upper 1 28.20** 106.28 88.90 102.26 58.60 43.75* 65.55 74.89
2 67.80 74.44 89.09 27.16* 88.12 46.97 69.56 89.57
1+2 45.69* 92.21 88.99 69.08 71.64 45.18* 67.32 81.39
80% lower 1 44.12* 86.27 118.49 52.94 23.25** 42.12* 49.69 78.85
2 76.08 60.06 114.11 33.49* 35.56* 76.48 56.75 62.41
1+2 58.26 74.69 116.55 44.36* 28.69** 57.31 52.82* 71.59







Table 3 Continued.
Mean yield per treatment as a percentage of the mean
yield of the controla,b
Defoliation Fruit Time of defoliation (in days after planting)
levels graded 30 40 50 60 70 80 90 100
80% upper 1 14.22** 49.94 50.71 54.73 41.90* 34.32* 38.40* 40.20*
2 29.58** 48.85 117.62 28.02* 63.60 43.26 49.82 61.74
1+2 21.01** 49.46* 80.27 42.93** 51.48* 38.27** 43.45** 49.72*
100% 1 4.24** 28.82** 34.38* 26.19** 12.83** 28.29** 50.93 39.18*
2 9.46* 11.61* 92.30 34.39* 39.16* 28.53* 31.85* 52.95
1+2 6.56** 21.23** 59.99 29.81** 24.46** 28.40** 42.50** 45.26*
a Mean yield per plant for the control: USDA grade 1, 323.3 g; USDA grade 2, 255.9 g.
b Yield is significantly different from the control if indicated by for P<0.05 or by ** for P<0.01.
c For an explanation of the defoliation level codes see page 4.
-. d Codes: 1 = USDA grade 1; 2 = USDA grade 2; 1+2 = USDA grades 1 plus 2.







Table 4. Influence of defoliation of 'Walter' tomato plants on the mean yield of all extra large plus large fruit in the second har-
vest of the spring crop of 1978.
Mean yield per treatment as a percentage of the mean
yield of the controla,b
Defoliation Fruit Time of defoliation (in days after planting)
level' graded 30 40 50 60 70 80 90 100
20% lower 1 92.19 78.42 137.48 77.84 101.25 101.62 158.10 115.76
2 97.56 95.27 81.10 102.13 76.52 170.73 244.97 117.38
1+2 93.90 83.87 119.11 85.71 93.15 124.07 186.35 116.23
20% upper 1 92.93 103.24 81.00 96.24 88.88 19.15 88.14 156.63
2 25.46 46.49 58.69 139.48 99.09 71.65 124.54 190.09
1+2 70.97 84.71 73.70 110.27 92.16 36.23 100.00 167.49
40% lower 1 155.38 116.13 135.13 151.84 122.24 138.44 172.31 115.98
2 98.62 89.18 102.44 89.94 120.43 193.14 111.28 153.20
1+2 136.82 107.30 124.42 131.61 121.59 156.18 152.36 128.04
40% upper 1 124.59 101.40 107.88 86.30 134.39 96.09 52.28 104.20
2 71.95 111.28 32.77 119.66 108.54 76.52 61.28 106.25
1+2 107.44 104.57 83.37 97.12 125.91 89.68 55.19 104.81
60% lower 1 159.79 69.59 94.77 95.51 178.72 39.40 58.32 71.43
2 190.85 125.00 70.43 78.51 125.76 101.37 167.99 115.09
1+2 169.83 87.59 86.85 89.93 161.39 59.55 94.04 85.61
60% upper 1 32.02 114.29 53.53 127.39 104.71 141.38 157.00 90.57
2 20.58 91.77 34.60 130.64 105.18 106.25 103.20 128.05
1+2 28.29 106.95 47.39 128.39 104.81 129.88 139.45 102.73
80% lower 1 44.70 57.95 157.58 104.57 94.77 119.07 12.67 65.32
2 21.65 86.89 67.38 158.54 155.03 88.41 123.48 187.04
1+2 37.22 67.34 128.14 122.08 114.39 109.03 48.73 104.96








Table 4 Continued.
Mean yield per treatment as a percentage of the mean
yield of the controla,b
Defoliation Fruit Time of defoliation (in days after planting)
levels graded 30 40 50 60 70 80 90 100
80% upper 1 27.61 54.12 6.77 114.87 31.30 67.01 72.90 42.12
2 0 89.94 9.91 210.67 97.10 104.42 113.57 113.11
1+2 18.61 65.76 7.79* 146.00 52.70 79.16 86.10 65.26
100% 1 16.72 53.02 30.71 29.46 41.38 39.03 49.85 62.22
2 34.30 49.85 52.59 77.29 84.60 119.97 28.96 75.76
1+2 22.43 51.96 37.82 45.01 55.43 65.36 43.03 66.60
a Mean yield per plant for the control: USDA grade 1, 135.8 g; USDA grade 2, 65.6 g.
b Yield is significantly different from the control if indicated by for P<0.05 or by ** for P<0.01.
c For an explanation of the defoliation level codes see page 4.
d Codes: 1 = USDA grade 1; 2 = USDA grade 2; 1+2 = USDA grades 1 plus 2.







Table 5. Influence of defoliation of 'Walter' tomato plants on the mean yield of all extra large plus large fruit in the first two
harvests of the spring crop of 1978.
Mean yield per treatment as a percentage of the mean
yield of the controla,b
Defoliation Fruit Time of defoliation (in days after planting)
level' graded 30 40 50 60 70 80 90 100
20% lower 1 96.47 94.62 110.45 103.99 118.62 107.84 61.24 61.02
2 135.17 99.35 81.53 92.88 66.08 121.11 109.20 93.59
1+2 112.40 96.56 98.54 99.40 96.97 113.29 81.00 74.43
20% upper 1 87.33 102.24 75.68 96.69 87.48 85.30 59.82 70.17
2 76.18 80.22 48.97 119.78 79.20 100.03 84.73 102.92
1+2 82.73 93.16 64.67 106.19 84.07 91.37 70.07 83.65
40% lower 1 98.21 90.16 127.87 109.54 88.89 93.21 69.03 74.52
S2 108.52 76.96 106.50 96.77 104.85 135.57 88.62 108.99
o 1+2 102.45 84.71 119.05 104.26 95.47 110.64 77.09 88.71
40% upper 1 90.16 121.23 86.35 89.18 113.50 80.29 51.33* 62.72
2 72.82 72.14 66.70 69.40 59.39 57.06 61.41 82.25
1+2 83.01 101.00 78.24 81.02 91.20 70.71 55.47 70.75
60% lower 1 108.23 73.50 96.95 103.38 65.37 63.52 77.64 94.99
2 137.75 59.70 92.26 98.73 84.89 98.48 70.49 76.65
1+2 120.37 67.81 95.02 101.45 73.40 77.92 74.68 87.42
60% upper 1 29.33** 108.67 78.51 109.69 72.23 72.63 92.60 79.53
2 58.15 77.95 77.95 48.26 91.57 59.08 76.40 97.39
1+2 41.20** 96.00 78.24 84.39 80.19 67.04 85.93 86.89
80% lower 1 44.32* 77.90 130.05 68.21 44.43* 64.90 38.76** 74.85
2 64.99 65.52 104.54 58.99 59.92 78.89 70.34 87.84
1+2 52.82 72.80 119.54 64.41 50.80 70.65 51.76 80.19







Table 5 Continued.
Mean yield per treatment as a percentage of the mean
yield of the control
Defoliation Fruit Time of defoliation (in days after planting)
level graded 30 40 50 60 70 80 90 100
80% upper 1 18.18** 51.18* 37.72** 72.52 38.76** 43.99* 48.61* 40.77**
2 23.54** 57.21 95.62 65.30 70.43 55.72 62.81 72.20
1+2 20.39** 53.66 61.56 69.54 51.80 48.82* 54.45 53.72
100% 1 7.95** 35.98** 33.32** 27.16** 21.28** 31.47** 50.63* 45.99*
2 14.52** 19.43** 84.17 43.13 48.41 47.17 31.25* 57.59
1+2 10.65** 29.16** 54.26 33.74** 32.46** 37.93** 42.64* 50.77
a Mean yield per plant for the control: USDA grade 1, 459.1 g; USDA grade 2, 321.5 g.
b Yield is significantly different from the control if indicated by for P<0.05 or by ** for P<0.01.
c For an explanation of the defoliation level codes see page 4.
IQ d Codes: 1 = USDA grade 1; 2 = USDA grade 2; 1+2 = USDA grades 1 plus 2.







Table 6. Influence of defoliation of 'Walter' tomato plants on the mean yield of all medium size fruit in the first harvest of the
spring crop of 1978.
Mean yield per treatment as a percentage of the mean
yield of the controla,b
Defoliation Fruit Time of defoliation (in days after planting)
level graded 30 40 50 60 70 80 90 100
20% lower 1 130.86 110.51 77.54 80.47 110.25 46.88* 25.09** 28.44**
2 176.07** 108.23 73.76 91.23 40.58* 89.87 32.29* 41.47*
1+2 151.85* 109.42 75.76 85.45 77.82 66.86 28.43** 34.49**
20% upper 1 105.87 112.16 78.83 70.07 100.82 102.78 30.91** 16.33**
2 175.65** 77.13 46.62 93.15 80.57 115.23 48.70 26.78**
1+2 138.29 95.87 63.83 80.77 91.38 108.54 39.17** 21.21**
40% lower 1 90.16 59.61 102.27 59.87 86.04 55.13 23.44** 33.59**
S2 68.42 70.62 79.98 56.10 89.45 65.46 43.25* 47.10
S1+2 80.03 64.74 91.87 58.13 87.60 59.92 32.64** 39.86**
40% upper 1 89.49 106.90 49.30 98.66 98.25 60.79 45.44* 19.17**
2 78.79 68.72 80.57 33.59* 40.40* 69.02 65.99 27.25**
1+2 84.49 89.12 63.83 68.37 71.35 64.60 54.96* 22.92**
60% lower 1 48.17 60.79 68.52 55.49 34.36** 62.18 66.05 80.22
2 72.69 68.54 72.27 54.50 59.36 63.80 47.51 41.88*
1+2 59.56 64.38 70.25 55.01* 46.01* 62.95 57.44 62.40
60% upper 1 63.73 92.22 72.39 76.76 53.43 35.29** 39.00* 40.03*
2 140.11 79.21 74.47 52.84 82.35 50.36 38.51* 49.88
1+2 99.23 86.14 73.33 65.52 66.86 42.29** 38.76** 44.63*
80% lower 1 57.96 41.06* 74.03 43.12* 35.03** 37.72* 61.57 27.56**
2 131.81 23.82** 70.50 34.95* 55.69 47.10 59.66 35.84*
1+2 92.29 33.06** 72.37 39.31** 44.63* 42.07** 60.66 31.40**







Table 6 Continued.
Mean yield per treatment as a percentage of the mean
yield of the controla,b
Defoliation Fruit Time of defoliation (in days after planting)
levels graded 30 40 50 60 70 80 90 100
80% upper 1 61.67 37.71* 66.98 56.00 38.23* 29.11** 47.40* 42.76*
2 73.16 34.95* 124.53 13.74** 48.28 38.92* 36.73* 33.47*
1+2 67.00 36.42** 93.72 36.36** 42.89** 33.66** 42.42** 38.43**
100% 1 17.36** 18.65** 33.85** 34.88** 18.29** 11.33** 34.00** 41.06*
2 31.10* 25.47** 62.62 40.11* 32.29* 11.97** 35.25* 54.32
1+2 23.75** 21.82** 47.25* 37.33** 24.79** 11.63** 34.57** 47.25*
a Mean yield per plant for the control: USDA grade 1, 194.1 g; USDA grade 2, 168.8 g.
b Yield is significantly different from the control if indicated by for P<0.05 or by ** for P<0.01.
c For an explanation of the defoliation level codes see page 4.
d Codes: 1 = USDA grade 1; 2 = USDA grade 2; 1+2 = USDA grades 1 plus 2.







Table 7. Influence of defoliation of 'Walter' tomato plants on the mean yield of all medium size fruit in the second harvest of the
spring crop of 1978.
Mean yield per treatment as a percentage of the mean
yield of the controlab
Defoliation Fruit Time of defoliation (in days after planting)
level graded 30 40 50 60 70 80 90 100
20% lower 1 53.35* 67.54 106.84 99.04 100.94 96.48 99.04 107.04
2 70.88 88.60 98.44 105.79 76.17 81.60 114.31 96.09
1+2 61.96** 77.88 102.71 102.35 88.78 89.17 106.54 101.66
20% upper 1 68.53 73.35 103.43 87.68 95.54 54.54* 73.27 90.01
2 48.10* 93.01 92.18 110.64 83.01 78.61 86.54 102.62
1+2 58.50** 83.01 97.91 98.96 89.39 66.36* 79.79 96.22
40% lower 1 142.08* 77.19 85.75 104.99 94.98 84.00 104.14 104.14
2 74.79 74.93 102.85 78.17 70.88 74.64 65.24 85.66
1+2 109.02 76.08 94.15 91.81 83.15 79.40 85.03 95.06
40% upper 1 90.30 100.37 104.00 79.60 85.13 118.81 92.79 90.15
2 87.19 83.51 89.19 108.93 71.76 71.32 68.38 82.63
1+2 88.78 92.10 96.72 94.01 78.56 95.50 80.80 86.47
60% lower 1 107.46 63.14 91.43 115.55 82.63 109.96 63.34 71.85
2 96.30 73.08 74.26 83.46 67.06 48.25* 113.49 86.60
1+2 101.99 68.02* 83.01 99.78 75.00 79.64 87.99 79.11
60% upper 1 79.31 89.67 67.40 80.36 49.66* 86.18 81.07 96.77
2 56.77 60.01 73.82 93.15 69.26 98.06 48.19* 75.73
1+2 68.24* 75.10 70.55 86.65 59.29** 92.03 64.92* 86.43
80% lower 1 38.51** 36.38** 86.12 52.70* 66.26 84.34 31.84** 67.96
2 35.56** 64.21 122.60 87.78 66.91 85.87 69.35 85.28
1+2 37.06** 50.05** 104.04 69.94* 66.58* 85.10 50.27** 76.47







Table 7 Continued.
Mean yield per treatment as a percentage of the mean
yield of the controla,b
Defoliation Fruit Time of defoliation (in days after planting)
level" graded 30 40 50 60 70 80 90 100
80% upper 1 46.88** 61.63 32.92** 90.01 35.19** 84.28 37.60** 50.14*
2 42.32** 54.86* 24.68** 78.52 74.79 67.59 64.85 54.28*
1+2 44.64** 58.32** 28.87** 84.38 54.64** 76.08 50.99** 52.19**
100% 1 27.44** 50.43* 34.82** 33.48** 26.39** 35.24** 27.10** 57.60*
2 25.33** 51.72* 59.80 80.28 57.95 39.23** 52.66* 54.28*
1+2 26.42** 51.06** 47.09** 56.47** 41.89** 37.20** 39.66** 55.97**
a Mean yield per plant for the control: USDA grade 1, 352.4 g; USDA grade 2, 340.3 g.
b Yield is significantly different from the control if indicated by for P<0.05 or by ** for P<0.01.
c For an explanation of the defoliation level codes see page 4.
t' d Codes: 1 = USDA grade 1; 2 = USDA grade 2; 1+2 = USDA grades 1 plus 2.
Cg1rd







Table 8. Influence of defoliation of 'Walter' tomato plants on the mean yield of all medium size fruit in the first two harvests
of the spring crop of 1978.
Mean yield per treatment as a percentage of the mean
yield of the controlab
Defoliation Fruit Time of defoliation (in days after planting)
level graded 30 40 50 60 70 80 90 100
20% lower 1 80.86 82.78 96.41 92.43 104.23 78.85 72.76 79.13
2 105.77 95.11 90.26 100.96 64.37* 84.36 87.12 77.98
1+2 92.87 88.73 93.44 96.54 85.01 81.51 79.68 78.57
20% upper 1 81.78 87.12 94.68 81.41 97.42 71.66 58.21** 63.85*
2 90.40 87.74 77.10 104.83 82.20 90.75 73.99 77.49
1+2 85.93 87.43 86.19 92.71 90.08 80.87 65.83* 70.42*
40% lower 1 123.62 70.93 91.60 88.95 91.79 73.73 75.47 79.07
2 72.68 73.50 95.27 70.85 77.04 71.60 57.94* 72.87
1+2 99.05 72.18 93.37 80.23 84.68 72.70 67.01* 76.08
40% upper 1 90.01 102.67 84.56 86.35 89.77 98.19 75.96 64.95*
2 84.40 78.61 86.33 83.97 61.38* 70.56 67.57 64.27*
1+2 87.31 91.07 85.41 85.20 76.08 84.87 71.92* 64.62**
60% lower 1 86.39 62.29 83.28 94.22 65.50* 92.97 64.31* 74.83
2 88.49 71.60 73.60 73.86 64.53* 53.43** 91.63 71.79
1+2 87.40 66.78* 78.62 84.39 65.02** 73.90 77.48 73.36
60% upper 1 73.77 90.56 69.15 79.07 50.99** 68.09* 66.14* 76.60
2 84.40 66.39 74.05 79.79 73.60 82.24 44.98** 67.18
1+2 78.90 78.90 71.51* 79.42 61.90** 74.92 55.93** 72.06
80% lower 1 45.41** 38.05** 81.81 49.30** 55.16** 67.78* 42.39** 53.60**
2 67.47 50.82** 105.32 70.26 63.19* 73.01 66.14 68.89
1+2 56.06** 44.21** 93.16 59.41** 59.03** 70.31* 53.85** 60.98**







Table 8 Continued.
Mean yield per treatment as a percentage of the mean
yield of the control
Defoliation Fruit Time of defoliation (in days after planting)
levels graded 30 40 50 60 70 80 90 100
80% upper 1 52.14** 53.15** 45.01** 77.94 36.26** 64.67* 41.07** 47.51**
2 52.54** 48.26** 57.79* 57.06* 66.00 58.08* 55.53** 47.38**
1+2 52.33** 50.79** 51.17** 67.87* 50.60** 61.50** 48.05** 47.45**
100% 1 23.87** 39.15** 34.49** 33.97** 23.51** 26.75** 29.55** 51.72**
2 27.24** 43.02** 60.74* 66.98 49.44** 30.19** 46.89** 54.31**
1+2 25.50** 41.01** 47.15** 49.89** 36.02** 28.42** 37.91** 52.97**
a Mean yield per plant for the control: USDA grade 1, 546.6 g; USDA grade 2, 509.1 g.
b Yield is significantly different from the control if indicated by for P<0.05 or by ** for P<0.01.
c For an explanation of the defoliation level codes see page 4.
S d Codes: 1 = USDA grade 1; 2 = USDA grade 2; 1+2 = USDA grades 1 plus 2.








DISCUSSION
Defoliation of unstaked fresh-market tomato plants revealed a
changing sensitivity to this type of damage in the course of their
development as was demonstrated for processing tomato (36), potato
(30) and sugarbeet (3).
Damage early in the development, before or at anthesis, when most
of the metabolic activity of the plant is directed at vegetative
development, seriously slowed plant growth. Defoliation at that time
may also affect the initial stages in ovary and embryo development,
resulting in reduced sizes of the fruit. Although Houghtaling (10)
postulated that the ultimate fruit size is determined early in fruit
development, defoliation around mid-season, both in Experiments
1 and 2, resulted in a reduction of the fruit size. This observation
suggests that mid-season is a critical time for photosynthate mobiliza-
tion to growing fruit. Defoliation of the tomato plants starting from
ground level (20% to 60% of the older foliage) had little, if any, ef-
fect on fruit set, development or quality, especially when the defolia-
tion occurred in the first two months of the season. Apparently,
foliage remaining on the plant is capable of synthesizing sufficient
amounts of nutrients necessary for the normal development of the
fruit. Since the canopy of unstaked tomato plants is normally very
dense, the lower leaves which are approaching senescence toward
the middle of the season will not contribute significantly to the
plant's net photosynthesis. They are probably beyond the compen-
sation point, using more photosynthate than they produce. The up-
per 20% to 40% of the foliage has in fact been shown to account
for more than half of the net photosynthetic activity of entire tomato
plants, since the upper leaf layers obviously intercept and utilize the
largest amount of light. In addition, defoliation has been found to
have a stimulatory effect on the remaining leaves, possibly even


Table 9. Influence of defoliation of 'Walter' tomato plants on the mean fresh
weight of all above-ground plant parts, excluding fruit, at the time
of completion of the third harvest of the spring crop of 1978.
Mean fresh weight per plant (in grams)ab
Defoliation Time of defoliation (in days after planting)
levels 30 60 100
80% lower 11062* 8080 6928
80% upper 10960* 7100 8175
100% 14177** 7595 7785
a Mean fresh weight per control plant: 8545 g.
b Weight is significantly higher from the control if indicated by for
P<0.05 or by ** for P<0.01.

28









resulting in an increase of 30% to 50% of the exported photosyn-
thates (14). The amount of nutrients entering the fruit apparently
also increased. The leaves remaining on the plant after many have
died due to leafminer infestation and subsequent disease develop-
ment are, therefore, well able to compensate for the loss of photosyn-
thetically active leaf area.
Removal of foliage from the tomato plant has an influence on both
temperature and air flow within the canopy. Especially high levels
of defoliation expose a large amount of the fruit to more direct sun
radiation. Subsequent temperature increase may influence the
metabolic equilibrium within the fruit, hastening the ripening pro-
cess, whereas under normal conditions division and enlargement of
the pericarp cells still would be the most important activities in the
fruit. This temperature change will have an especially profound ef-
fect when the ripening process is well under way, towards the end
of the season when the plants' energy production is almost entirely
directed toward reproductive development. Replacement of vegeta-
tion removed is then negligible and damage to the fruit by sunscald




300 USDA grade 2 second harvest
I USDA grade 2
E
i R~yi USDA grade T i-
S250 -
a a

> 200 -
z

I Ia
. 150 -
first harvest
I.-
a
S 100


Y 50
U ab b ab



0 20U 40L 40U 0 20U 40L 40U

DEFOLIATION LEVEL

Figure 9. Influence of repeated defoliation of 'Walter' tomato plants on
the mean yield of all medium-sized fruit (6 defoliations).


29








and decay becomes more likely. Sunscald may not occur if defolia-
tion is a week or less before harvest but the ripening process will
still be favored over cell enlargement. Yield loss due to sunscald may
be prevented if the fruit can be harvested earlier than normal
although this would only be applicable if the entire field were
defoliated to the same extent and there were no border effects.
If the defoliation is serious enough to expose a large number of
flower clusters to direct sun radiation, fertilization may be affected.
Shading has been shown to affect the percentage of misshapen fruit;
higher levels of shade increasing this percentage (19). On the other
hand, exposure may mean temperature increases to levels where
fruit set may be affected (17). Inadequate fertilization causes poor
locular jelly development and the resulting fruit are misshapen. This



first harvest I USDA grade
800
a USDA grade 1

700


600
S oo
C b
- 500

Sb



300
second harvest

200


100



0 20U 40L 40U 0 20U 40L 40U
DEFOLIATION LEVEL


Figure 10. Influence of repeated defoliation of 'Walter' tomato plants on
the mean yield of all extra large plus large fruit (6 defoliations).


30









may explain not only why the total weight of culled fruit did not
drop proportionally to the total yield but also why yield reduction
usually occurred in the USDA grade 1 fruit and not in the grade 2
fruit. The combination of these two effects could compensate each
other and, although changes in fruit number and quality of an en-
tire plant will be affected, the number of marketed fruit would re-
main the same.



first harvest s
small
900
a FRUIT I medium
SIZES 00 large

800 am extra large



700

I IN
S600 b
Sb
I- second harvest
z
S500 a a
I Po

G, a
i0 400
Oo


0 300 0



200



100




0 20U 40L 40U 0 20U 40L 40U
DEFOLIATION LEVEL




Figure 11. Influence of repeated defoliation of 'Walter' tomato plants on
the mean total yield of all marketable fruit (6 defoliations).


31








Since the leafminers usually attack the lower and middle leaves
first (34) their effect on net photosynthesis will be minimal. The
younger (upper) leaves, which are the most important to the plant
and the removal of which would harm the plant more than the
removal of the older (lower) ones (6), are normally only slightly
damaged. Only in case of very serious outbreaks of leafminers will
the mine intensity in the upper portion of the plant increase
dramatically and pose a threat to fruit production.
Repeated defoliation at lower levels (20% to 60%) reduces the yield
of the first harvest as much as a high level defoliation does over a
short period of time. Vigor and transpiration are more severely af-
fected and the plant diverts a large portion of its energy supply to
the healing process, delaying development of both vegetative growth
and fruit development. In comparison to similar foliar damage in
staked tomatoes, one would expect less reduction of fruit yield in
the unstaked plants. That at least 60% of the foliage has to be remov-
ed to significantly reduce yield of staked 'Walter' tomatoes (13) is
probably due to the fact that in those experiments no damage was
inflicted to the plants in the especially sensitive prebloom period.
The minimal reduction of total yield in the repeated defoliation ex-
periments in this study shows that the overall response of the tomato
plants to defoliation is very similar in staked and unstaked tomatoes.
However, continuous leaf abscission due to infection of even small
numbers of leafmines is a more gradual process than repeated
mechanical defoliation and may, therefore, be less detrimental to
the plant.
A reduction in the weight of extra large and large fruit is the more
serious effect of high levels of defoliation at different times. Since
these two largest fruit sizes account for the largest portion of the
grower's revenue from the tomato crop, a reduction in their weight
will more severely reduce his total income.
Although the weight of the medium-sized fruit may be reduced,
the effect of this reduction is a relatively small component of the
total net return to the producer.
In the present study all marketable fruit was harvested, irrespec-
tive of its position within the canopy. In a tomato grower's field this
may not be the case. Pickers will easily overlook some mature fruit,
especially the smaller sizes, if the plant's foliage is very dense.
Defoliation resulting from leafminer infestations followed by disease
development, especially in the last weeks before harvest may
therefore be an advantage. Even if the actual fruit set is reduced
and the absolute number of extra large and large fruit is less than
that of non-defoliated plants, the amount of fruit picked from the
defoliated plants and shipped may well be equal or even greater than

32











1250 small
FRUIT I medium
SIZES large
IEJI extra large

a


1000



a





750









500









250 --










0% 20% 40% 40%
upper lower upper

DEFOLIATION LEVEL




Figure 12. Influence of repeated defoliation of 'Walter' tomato plants on
the mean total yield of all marketable fruit in the first two

harvests (6 defoliations).


33
0 '* 0 0* 0>000
W 0000 ~ ~ 00~000



o0% 2000 400000
upper0 loe 0upper000
DEFOL 00000N00EVE


Fiur 500 Inlec 00rpae eoito f Wle'tmt lnso
tematotal~ yield of 0 al0aktbl 0ri0nth is w
harests (6deolaton)
000 00 000330








that originating from healthy plants. In fact the use of defoliants
to increase the number of fruit picked has been suggested (32).
Considering the differential sensitivity to defoliation in the course
of the development of the tomato plants, the economic threshold
of the leafminers varies during the season. Monitoring of the infesta-
tion levels is especially advisable early in the season and at mid-
season.

CONCLUSION
Depending on the time and the intensity of leafminer outbreaks,
the effect of defoliation, resulting from infestation of tomato plants,
on both fruit yield and quality varies. Low levels of defoliation are
tolerated very well by the tomato plants since the remaining foliage,
which nearly always consists of actively photosynthesizing tissue,
is responsible for nearly all the nutrient supply necessary for fruit
development. Even occasional intermediate defoliations do not result
in yield losses. Repeated defoliation at intermediate levels can be
detrimental to yield and quality of the tomatoes because there is
more continuous interference with the plants' metabolism and diver-
sion of the energy supply from the fruit to the vegetative parts of
the plants in order to optimize its photosynthetically active leaf area.
Before and at anthesis, the removal of foliage interferes most with
subsequent fruit development because of possible growth delay and
impaired fertilization. At mid-season, increased sensitivity to defolia-
tion also occurs with the interference of nutrient translocation from
the leaves to the fruit.
The following recommendations can be made to the producer. If
the defoliation level of the lower canopy in the period before bloom
exceeds 30%, specific insecticidal treatment for leafminer control
should be applied. After bloom, no control measures need be under-
taken until defoliation exceeds the 50% level. If, after specific in-
secticidal treatments for leafminer control have been applied, a fur-
ther defoliation of 10% or more occurs, additional treatments are
needed. In general, if defoliation levels throughout the season do
not exceed 30% in the lower canopy, no specific insecticidal
treatments for leafminer control are warranted.









34







Table 10. Influence of defoliation of 'Walter' tomato plants on the mean yield of all extra large plus large fruit in the first
harvest of the fall crop of 1978.
Mean yield per treatment as a percentage of the mean
yield of the controla,b
Defoliation Fruit Time of defoliation (in days after planting)
level graded 30 40 50 60 70 80
60% upper 1 65.71 82.54 46.01** 105.48 102.45 150.27*
2 60.55 41.35 101.97 75.61 76.47 82.01
1+2 64.36* 71.77 60.63** 97.67 95.65 132.42*
80% lower 1 53.01* 81.74 85.90 94.35 86.17 128.76
2 40.48 71.70 104.57 88.75 130.45 84.26
1+2 49.73** 79.11 90.77 92.88 97.73 117.12
80% upper 1 47.50** 79.17 76.24 69.38 102.57 111.36
2 45.92 57.51 106.12 58.37 73.36 97.65
CA 1+2 47.09** 73.51 84.04 66.50* 94.93 107.76
100% 1 31.75** 31.23** 36.22** 63.69 95.17 114.62
2 24.91* 60.21 55.26 56.12 54.91 74.29
1+2 29.96** 38.80** 41.19** 61.71** 84.65 104.09
a Mean yield per plant for the control: USDA grade 1, 408.6 g; USDA grade 2, 144.5 g.
b Yield is significantly different from the control if indicated by for P<0.05 or by ** for P<0.01.
c For an explanation of the defoliation level codes see page 4.
d Codes: 1 = USDA grade 1; 2 = USDA grade 2; 1+2 = USDA grades 1 plus 2.







Table 11. Influence of defoliation of 'Walter' tomato plants on the mean yield of all extra large plus large fruit in the second
harvest of the fall crop of 1978.
Mean yield per treatment as a percentage of the mean
yield of the controla,b
Defoliation Fruit Time of defoliation (in days after planting)
level' graded 30 40 50 60 70 80
60% upper 1 64.18* 78.12 28.80** 63.05* 45.06** 63.53*
2 85.16 130.50 64.50 126.03 113.35 103.80
1+2 68.15 88.02 35.55** 74.96 57.98* 71.14
80% lower 1 68.33 27.49** 35.04** 31.85** 46.45** 36.73**
2 159.36 54.55 136.84 136.47 39.67 53.84
1+2 85.55 32.58** 54.31** 51.65** 45.16** 39.97**
80% upper 1 79.78 55.73** 25.66** 35.82** 49.68** 38.35**
2 27.74 74.72 74.72 110.51 50.71 63.53
1+2 69.92 59.32* 34.96** 49.96** 49.86** 43.11**
100% 1 63.01* 15.55** 6.62** 23.39** 26.88** 37.39**
2 74.35 49.96 65.62 100.67 51.45 31.69
1+2 65.14 22.06** 17.80** 38.02** 31.53** 36.30**
a Mean yield per plant for the control: USDA grade 1, 286.9 g; USDA grade 2, 67.0 g.
b Yield is significantly different from the control if indicated by for P<0.05 or by ** for P<0.01.
c For an explanation of the defoliation level codes see page 4.
d Codes: 1 = USDA grade 1; 2 = USDA grade 2; 1+2 = USDA grades 1 plus 2.







Table 12. Influence of defoliation of 'Walter' tomato plants on the mean yield of all medium-sized fruit in the first harvest of
the fall crop of 1978.
Mean yield per treatment as a percentage of the mean
yield of the controla,b
Defoliation Fruit Time of defoliation (in days after planting)
levelF graded 30 40 50 60 70 80
60% upper 1 150.33 150.33 121.64 161.80 74.10 122.13
2 90.63 81.01 201.92 99.04 124.28 84.13
1+2 126.10 122.20 154.04 136.32 94.45 106.62
80% lower 1 114.75 138.85 163.44 194.59 114.26 133.11
2 103.37 104.57 124.28 131.01 164.66 91.35
1+2 110.03 124.83 147.52 168.65 134.57 116.07
80% upper 1 132.20 99.18 121.31 125.41 164.75 149.28
2 121.88 71.39 185.10 102.64 70.91 78.13
1+2 128.04 87.83 147.03 116.07 126.58 120.25
100% 1 65.08 57.38 162.30 126.23 129.51 251.97**
2 67.31 38.46 199.52 50.48 124.28 165.87
1+2 65.92 49.66 177.22 95.42 127.26 216.85**
a Mean yield per plant for the control: USDA grade 1, 30.5 g; USDA grade 2, 20.9 g.
b Yield is significantly different from the control if indicated by for P<0.05 or by ** for P<0.01.
c For an explanation of the defoliation level codes see page 4.
d Codes: 1 = USDA grade 1; 2 = USDA grade 2; 1+2 = USDA grades 1 plus 2.







Table 13. Influence of defoliation of 'Walter' tomato plants on the mean yield of all medium-sized fruit in the second harvest
of the fall crop of 1978.
Mean yield per treatment as a percentage of the mean
yield of the controla,b
Defoliation Fruit Time of defoliation (in days after planting)
levels graded 30 40 50 60 70 80
60% upper 1 100.32 101.88 53.72* 35.65** 53.43* 77.63
2 92.25 121.71 114.50 117.98 150.39 129.22
1+2 98.81 105.60 65.14* 51.11** 71.62 87.32
80% lower 1 93.91 57.40* 48.86** 34.85** 41.17** 26.49**
2 108.53 56.74 150.54 183.72* 47.67 56.98
1+2 96.66 57.29** 67.94* 62.77* 42.39** 32.21**
80% upper 1 81.26 63.63 33.60** 39.59** 45.14** 48.33**
2 74.03 71.32 123.02 81.78 61.78 44.96
o 1+2 79.90 65.07* 50.39** 47.51** 48.28** 47.70**
100% 1 76.16 49.97** 14.44** 18.53** 37.98** 46.39**
2 98.99 59.46 135.43 167.44 53.64 51.16
1+2 80.44 51.77** 37.15** 46.46** 40.93** 47.29**
a Mean yield per plant for the control: USDA grade 1, 279.4 g; USDA grade 2, 64.5 g.
b Yield is significantly different from the control if indicated by for P<0.05 or by ** for P<0.01.
c For an explanation of the defoliation level codes see page 4.
d Codes: 1 = USDA grade 1; 2= USDA grade 2; 1+2 = USDA grades 1 plus 2.








REFERENCES CITED
1. Acock, B., D. A. Charles-Edwards, D. J. Fitter, D. W. Hand, L.
W. Ludwig, J. Warren Wilson, and A. C. Withers. 1978. The con-
tribution of leaves from different levels within a tomato crop
to canopy net photosynthesis: An experimental examination of
two canopy models. J. Exp. Bot. 29:815-827.
2. Adlerz, W. C. 1961. Control of leaf miner on watermelon in cen-
tral and south Florida. Proc. Fla. State Hort. Soc. 74:134-137.
3. Capinera, J. L. 1979. Effect of simulated insect herbivory on
sugarbeet yield in Colorado. J. Kans. Entomol. Soc. 52:712-718.
4. Capinera, J. L., and W. J. Roltsch. 1980. Response of wheat
seedlings to actual and simulated migratory grasshopper defolia-
tion. J. Econ. Entomol. 73:258-261.
5. Elmore, J. C., and C. A. Ranney, Jr. 1954. Injury to pepper plants
by the pea leaf miner. J. Econ. Entomol. 47:357-358.
6. Harper, J. L. 1977. Population biology of plants. Academic Press,
New York. 892 pp.
7. Harris, P. 1972. Insects in the populations dynamics of plants.
Pp. 201-209 in H. F. van Emden (ed.) Insect/plant relationships.
Blackwell Scientific Publications, Oxford. 215 pp.
8. Harris, P. 1974. A possible explanation of plant yield increases
following insect damage. Agro-Ecosystems 1:219-225.
9. Hills, O. A. and E. A. Taylor. 1951. Parasitization of Dipterous
leaf miners in cantaloupe and lettuce in the Salt River Valley,
Arizona. J. Econ. Entomol. 44:759-762.
10. Houghtaling, H. B. 1935. A development analysis of size and
shape in tomato fruit. Bull. Torrey Bot. Club 62:242-252.
11. Johnson, M. W., E. R. Oatman, and J. A. Wyman. 1980a. Ef-
fects of insecticides on populations of the vegetable leafminer
and associated parasites on summer pole tomatoes. J. Econ. En-
tomol. 73:61-66.
12. Johnson, M. W., E. R. Oatman, and J. A. Wyman. 1980b. Ef-
fects of insecticides on populations of the vegetable leafminer
and associated parasites on fall pole tomatoes. J. Econ. Entomol.
73:67-71.
13. Jones, J. P. 1980. Tolerance of tomato to manual defoliation.
Proc. Fla. State Hort. Soc. 92:99-100.
14. Khan, A., and G. R. Sagar. 1969. Alteration of the pattern of
distribution of photosynthetic products in the tomato by
manipulation of the plant. Ann. Bot. 33:753-762.
15. Levins, R. A., S. L. Poe, R. C. Littell, and J. P. Jones. 1975. Ef-
fectiveness of a leafminer control program for Florida tomato
production. J. Econ. Entomol. 68:772-774.


39








16. McGregor, E. A. 1914. The serpentine leaf-miner on cotton. J.
Econ. Entomol. 7:447-454.
17. Marlowe, G. A., Jr. 1977. Some causes of poor fruit set in
tomatoes. Pp. 6, 7 in Univ. Fla. Vegetarian Newsletter. 77-11.
10 pp.
18. Marlowe, G. A., Jr. 1978. Harvesting and handling. Weight-size
relationship. Pp. 8-10 in Univ. Fla. Vegetarian Newsletter. 78-9.
12 pp.
19. Marr, C., and I. G. Hillyer. 1968. Effect of light intensity on
pollination and fertilization of field and greenhouse tomatoes.
Proc. Am. Soc. Hort. Sci. 92:526-530.
20. Michelbacher, A. E., W. W. Middlekauff, and L. C. Glover. 1951.
Studies with aldrin and dieldrin against melon insects. J. Econ.
Entomol. 44:390-393.
21. Oshima, R. J., O. C. Taylor, P. K. Braegelmann, and D. W.
Baldwin. 1975. Effect of ozone on the yield and plant biomass
of a commercial variety of tomato. J. Environ. Qual. 4:463-464.
22. Pena, J. E. 1983. Tomato pinworm, Keiferia lycopersicella
(Walsingham): population dynamics and assessment of plant in-
jury in southern Florida. Univ. Fla. Ph.D. Dissertation. 265 pp.
23. Pohronezny, K. and R. B. Volin. 1983. Yield and quality losses
in fresh market tomato production due to bacterial spot. Hort-
Science 18:69-70.
24. Pohronezny, K., R. B. Volin, and R. E. Stall. 1979. An outbreak
of bacterial speck on fresh-market tomatoes in south Florida.
Plant Dis. Rep. 63:13-17.
25. Pohronezny, K., V. H. Waddill, W. M. Stall, and W. Dankers.
1978. Integrated control of the vegetable leafminer (Liriomyza
sativae Blanchard) during the 1977-78 tomato season in Dade
County, Florida. Proc. Fla. State Hort. Soc. 91:264-267.
26. Richards, M. C. 1947. Lack of correlation between yield and
disease control with fungicides. Phytopathology 37:18-19.
27. Romshe, R. A. 1939. Correlation between fresh weight and area
of tomato leaves. Proc. Am. Soc. Hort. Sci. 36:482.
28. Schuster, D. J., and P. H. Everett. 1977. Leafminer and tomato
pinworm chemical control research update. Univ. Fla. Braden-
ton AREC Res. Rep. GC1977-6. 6 pp.
29. Schuster, D. J., J. P. Jones, and P. H. Everett. 1976. Effect of
leafminer control on tomato yield. Proc. Fla. State Hort. Soc.
89:154-156.
30. Skuhravy, V. 1968. Einflusz der Entblatterung und des Kartof-
felkaferfraszes auf die Kartoffelernte. Anz. Schaedlingskd.
41:180-188.



40








31. Steel, R. G. D., and J. H. Torrie. 1960. Principles and procedures
of statistics. McGraw-Hill Book Company, New York. 481 pp.
32. Vittum, M. T. 1957. Tomato defoliation. Am. Veg. Grower
5:20-21.
33. Wiebe, J. 1970. Foliage canopy effects in greenhouse tomatoes.
Hort. Res. Inst. Ont. Rep. 1969:108-113.
34. Wilcox, J., and A. F. Howland. 1952. Control of a Dipterous leaf
miner on tomatoes in California. J. Econ. Entomol. 45:634-639.
35. Wolfenbarger, D. A. 1966. Variations in leafminer and flea bee-
tle injury in tomato varieties. J. Econ. Entomol. 59:65-68.
36. Wolk, J. O., D. W. Kretchman, and D. G. Ortega, Jr. 1983.
Response of tomato to defoliation. J. Am. Soc. Hort. Sci.
108:536-540.



































41





University of Florida Home Page
© 2004 - 2010 University of Florida George A. Smathers Libraries.
All rights reserved.

Acceptable Use, Copyright, and Disclaimer Statement
Last updated October 10, 2010 - - mvs