EFFECT OF THE VEGETABLE LEAFMINER, Liriomyza sativae BLANCHARD, AND THE ASSOCIATED PLANT PATHOGENS ON YIELD AND QUALITY OF THE TOMATO, Lycopersicon esculentum MILL. CV. WALTER By JOZEF LEO WILLEM KEULARTS DISSERTATION PRESENTED TO THE GRADUATE COUNC! OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY :» ; t i/r ^->c T TV ^ C -""' riDTI Voor mijn ouders, Leo en Maria Keularts, in dankbaarheid en toewijding ACKNOWLEDGEMENTS I would like to thank many people for their cooperation and support: Dr. Van H. Waddill, my advisor and chairman of my committee, for his constructive suggestions, his constant availability to help, and his confidence in me and in this project. Dr. Kenneth L. Pohronezny for his practical help, sharing ideas, serving on my committee, and positive criticisms. Drs. Robert T. McMillan, Jr., and John R. Strayer for their in- terest and cooperation in serving on my committee. Dr. Thomas L. Davenport for sharing his laboratory facilities and his expertise in photosynthesis studies and gas chromatography. Dr. Carol A. Musgrave for sharing her research experience and exchanging ideas. Dr. Stratton H. Kerr for his continuous sound advice and encourage- ment both before my entrance to and throughout my progress in this course of study. The entire staff of the University of Florida Agricultural Research and Education Center in Homestead for their cooperation, particularly Whitaya Chaisit, Rodney Chambers, Wilbur Dankers, Phyllis Daum, Joyce Francis, Charla Phillips, and Steven Williams, whose voluntary help and enthusiastic support in the arduous task of grading tomatoes will never be forgotten. Jorge Pena, for his encouraging sense of humor and friendship as well as his help in data collection. The Florida Tomato Exchange and the Center for Environmental Programs and Natural Resources whose financial support made this pro- ject possible. Mia, my 22-month-old daughter, whose birth and life brought sorely needed moments of joy and laughter to the tedium of study. My wife, Mary Jane Provost, who encouraged me to take up this study, for her steadfast support and patience, but especially for being my wife. IV TABLE OF CONTENTS ACKNOWLEDGEMENTS i i i ABSTRACT vi i i CHAPTER I INTRODUCTION 1 II A REVIEW OF THE LITERATURE ON THE IDENTIFICATION AND CONTROL OF THE VEGETABLE LEAFMINER, Liriomyza sativae BLANCHARD 5 Introduction 5 Identification of the Vegetable Leafminer 6 Control of the Vegetable Leafminer 8 Control by Parasites 8 Cultural Control 16 Control by Host Plant Resistance 16 Chemi cal Control 17 Conclusions 19 III MECHANICAL DEFOLIATION OF THE TOMATO, Lycopersicon esculenrum MILL. CV. WALTER, AND ITS EFFECT ON YIELD AND FRUIT QUALITY 20 Introduction 20 Materi al s and Methods 23 General 23 One-Time Defoliation 24 Experiment 1 25 Experiment 2 27 Experiment 3 27 Repeated Defoliation 27 Experiment 4 28 Experiment 5 28 Gross Revenue Computation 28 Resul ts 28 Experiment 1 28 Experiment 2 32 Experi ment 3 33 Experiment 4 35 Experiment 5 36 Discussion 36 Conclusion 113 IV MICRO-ORGANISMS ASSOCIATED WITH MINES OF Liriomyza sativae BLANCHARD 115 Introduction 115 Materials and Methods 116 Isolation from Leaves 116 Pathogenicity Tests , 118 Fungal tests 118 Bacterial tests 119 Isolation from Flies 119 Resul ts 121 Symptoms 121 Isolations from Leaves and Flies 121 Discussion 127 Conclusions 131 VI V EFFECT OF THE VEGETABLE LEAFMINER, Liriorcyza sativae BLANCHARD, ON THE PHOTOSYNTHETIC ACTIVITY OF INDIVIDUAL TOMATO LEAFLETS 133 Introducti on 133 Materials and Methods 133 Resul ts 134 Discussion 135 Conclusions 137 VI CONCLUSIONS 140 REFERENCES CITED 143 BIOGRAPHICAL SKETCH 154 Abstract of Dissertation Presented to the Graduate Council of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy EFFECT OF THE VEGETABLE LEAFMINER, Liriomyza sativae BLANCHARD, AND THE ASSOCIATED PLANT PATHOGENS ON YIELD AND QUALITY OF THE TOMATO, Lycopersicon esculentum MILL. CV. WALTER 3y JOZEF LEO WILLEM KEULARTS August 1980 Chairman: Dr. Van H. Waddill Major Department: Entomology and Nematology In the period from 1977 to 1980 a number of field experiments were carried out at the University of Florida Agricultural Research and Education Center in Homestead to determine the effect of various levels of discrete or repeated, mechanical defoliation of 'Walter1 tomato plants on components of marketable yield. Treatments consisted of 100% defoliation and separate 20%, 40%, 60%, and 80% defoliations of the lower or the upper part of the plants. A differential sensitivity to defoliation in the course of the plants' development was observed. The most sensitive times appeared to be early in the season and at mid-season. In most cases, however, at least 60% of the foliage had to be removed before total marketable fruit yields and yields in the largest, most profitable size categories were significantly reduced when compared to yields from the control plants. Tomato plants exhibited less tolerance of repeated defoliation with removal of 40% of the total leaf area often resulting in yield loss in the first harvest. However, the total yield of the first two harvests combined was not significantly reduced when compared to yields from nondefoliated plants. The total marketable yield of the tomato plants at any level of defoliation was significantly correlated with the gross revenue a grower would obtain from the harvested fruit based on different prices for the various size categories. Major defoliation associated with leafminer damage in commercial production plantings is the result of the adverse effect of pathogens inhabiting the leaf mines. In this study the pathogen most commonly associated with the leaf mines has been identified as Alternaria alternata (Fries) Keissler. It appears to be only weakly parasitic, its detrimental effect depending on the nutrient supply provided in the mine by mesophyll cells lacerated by the leafminer larvae. 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O ■r— r— S- 2 ra +" > CO co 3 3 CiJ OJ +-> +J '71 CO o O s_ i. aj 01 CJ a coll I 14 c c IT! -a & s- +-> (0 01 ac o £= c ■I— ■+-> 01 03 f0 r- m o c Ol i — 0) o; U1 . #1 ^n l/l +-> r-^ r~~. C 00 f^. (Ti 0) * . 03 •» >,LT> CI c -o i£> i— < 4-1 CD JC C .— i IT! c u 0) C (1) n 03 ^ CT1 i — 03 C -C <-o S_ <_> ■o • i — OJ .o CT U C T3 o cr, t/> S (O s. ^ i — i s_ 03 U_ r— 0) QJ OJ r<3 03 03 03 o> > > > T3 +J •ZZ O +J -l-> +-> 3 03 Spa •21 15 i. c_> -r- QJ E E en QJ rD i— > f (V M CD >, a; -C T- ai o 16 1977). A Geocoris species has been observed by the author to attack leafminer pupae on plastic mulch underneath the tomato canopy. Cultural Control Abandoned tomato fields could be an important factor in contributing to the leafminer problem (Adlerz, 1961). It has been recommended that plants and plant debris remaining in the field after the final harvest be destroyed to eliminate this fly source (Brogdon, 1961; Wolfenbarger, 1961). However, others feel that abandoned fields contribute few vegetable leafminers to the agroecosystem (K. Pohronezny and V.H. Waddill, personal communication, 1980). Use of various types of mulching has on several occasions been shown to decrease the number of leaf mines of _L. sativae in tomato and squash (Wolfenbarger and Moore, 1968; Chalfant et al . , 1977). An in- crease, using plastic coated paper as the mulch, was found also (Price and Poe, 1976). Staking has been shown to increase the leaf mine density and de- crease parasitism of the leafminer by dpi us dimidiatus (Price and Poe, 1976). Control by Host Plant Resistance Differential response of Liriomyza sativae Blanchard in cantaloups, chrysanthemums, muskmelons, and tomatoes has been found (Kelsheimer, 1963; Wolfenbarger, 1966; Webb and Smith, 1969; Webb et al . , 1971; Kennedy et al., 1975, 1978; Schuster and Harbaugh, 1979). These dif- ferences in resistance in the tomato cultivars were not great although 17 several accessions of species related to the cultivated tomato were virtually immune or demonstrated a considerable antibiosis (Webb and Smith, 1969; Webb et a!., 1971). A relatively low level of leafminer resistance in tomato may sufficiently reduce leafminer damage to provide adequate control (Webb et al., 1971). Chemical Control Since the vegetable leafminer became a major pest on various truck crops in the mid-1940's, many insecticides have been applied to reduce its populations. DDT has been shown ineffective against leafminers and, because of the reduction of their parasite populations, actually caused an increase in the fly population (Hills and Taylor, 1951; Shorey and Hall, 1963). Research on insecticidal control of the leafminer has been intensive (Mus grave et al., 1975). A large number of compounds has been shown to be promising, but the effectiveness of several has decreased over years of use. Chlordane was one of the first insecti- cides recommended for leafminer control (Wolfenbarger, 1947). Toxa- phene, parathion, aldrin, and dieldrin were also effective in the 1940 ' s (Wolfenbarger, 1948, 1958; Michelbacher et al . , 1951; Wene, 1953). All these products, however, seemed to be losing their effectiveness (Wolfenbarger, 1958; Baranowski, 1958; Wene, 1955). Toxaphene, para- thion, and aldrin were shown to reduce the parasite population without directly affecting the leafminers (Wene, 1955). In the mid-1950's diazinon became the most effective insecticide (Baranowski, 1958; Wolfenbarger, 1958), although it was ^ery toxic to some parasites 18 (Getzin, 1960). Brogdon (1961) and Adlerz (1961) found that diazinon was no longer effective in 1961 in south Florida but that it still controlled leafminer populations in north and central Florida. Good reduction of the fly population on tomato with diazinon was also ob- tained in California (Shorey and Hall, 1963). Dimethoate was shown to be yery effective in controlling leafminers in the late 1950' s (Getzin, 1960; Hayslip, 1961; Wolfenbarger, 1961). Getzin (1960) found that dioxathion gave excellent control; on the other hand, Harris (1962) found it to be ineffective. Harding (1971) noted good control of the vegetable leafminer on tomato with methamidophos, monocrotophos, and dimethoate in Texas. These three compounds were also effective on tomato in south Florida in 1976 (Schuster et al . , 1976). However, dimethoate is not considered effective against the leafminer anymore (Pohronezny and Waddill, 1978). Oxamyl gave good control of leafminer on tomato in south Florida in 1974 (Bear, 1975) and in 1975 (Schuster et al . , 1975). In 1977, however, control of defoliation of tomatoes by applications of oxamyl was not satisfactory (Schuster and Everett, 1977). Janes and Genung (1977) also found no control of the vegetable leafminer on celery with this insecticide. The use of methomyl for the control of Lepidopterous pests of tomato destroys the parasite population and subsequently increases the leafminer densities (Oatman and Kennedy, 1976; Janes and Genung, 1977; Johnson et al., 1980a, b). The negative effects of juvenile hormone analogs on biological control agents appear to outweigh the beneficial effects on target pests (Poe, 1974; Lema and Poe, 1978). Synthetic pyrethroids like permethri.n seem to give excellent control of leafminer populations (Schuster et al., 1975; Janes and Genung, 1977; Tryon, 1979) and are 19 relatively non-toxic to some of the parasites (Waddill, 1978). This group of compounds may be a good alternative to the conventional in- secticides because of the spectrum of activity and low toxicity to parasites and mammals (Schuster et al . , 1975). Conclusions It would be reasonable to suggest that the vegetable leafminer, Liriomyza sativae Blanchard, has become resistant to many insecticides since many of these chemicals have been ineffective in reducing the leafminer populations. Before the development of DDT and other chlorinated hydrocarbons, the leafminer had never been considered a problem in tomato production. Apparently its population was kept suf- ficiently low by natural enemies. The list of Hymenopterous parasites recorded for I. sativae illustrates the large number of natural enemies of this pest species. Since neither host plant resistance nor cultural methods have as yet been capable of reducing leafminer populations effectively, the solution to the problem seems to lie in integration of chemical and biological control. Allowing the parasite population to build up rapidly as early in the season as possible would be of great value. This may be accom- plished by maintaining the parasite population on weeds or crops grown outside the normal growing season. This is applicable to south Florida, especially since year-round cultivation of crops is possible. The application of selective insecticides for control of the Lepidopterous pests only when needed instead of on the basis of a regular application schedule -would be very beneficial to the leafminer's natural enemies since it would aid in the buildup of parasite populations. CHAPTER III MECHANICAL DEFOLIATION OF THE TOMATO, Lycopersicon esculentum MILL. CV. WALTER, AND ITS EFFECT ON YIELD AND FRUIT QUALITY Introduction Several 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. Damage by the vegetable leafminer, Liriomyza sativae Blanchard, in contrast, is restricted to the leaves and the injury is different from that caused by most foliage feeders. Only the leaves' mesophyll is consumed (even the spongy tissue remains for the most part untouched) leaving both upper and lower epidermis intact. The presence of a large number of leafminer larvae within one leaf may result in such a serious impairment of the functions of this plant organ that leaf death and subsequent abscission occurs. In addition to this type of damage, yellowing and necrosis of the leaf tissues in the mines' vicinity may occur, even if the larval population is small, again possibly resulting in abscission of the entire leaf. It is clear that, in the case of serious leafminer infestations, partial or even complete defoliation of tomato plants may occur. In recent years the population of the vegetable leafminer has become sc large that growers consider this insect as their most serious pest 20 21 (Pohronezny et al . , 1978b). 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 or reproductive capacity (Harris, 1972). In fact, Harris (1974) 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 (Skuhravy, 1968). Despite many attempts to find a correlation between leafminer damage and tomato yield no consistent results were obtained. Naturally occurring leafminer populations and insecticide-induced populations have been found to have no significant effect on tomato yield (Levins et al . , 1975; Schuster and Everett, 1977; Johnson et al . , 1980a, b) although in some fields and in some years yield reduction was found (Wolfenbarger and Wolfenbarger, 1966; Schuster et al., 1976). Many references have been made to serious leafminer damage of cultivated plants (Spencer, 1973a; Spencer and Stegmaier, 1973) but only on a few occasions has an indirect reduction of yield of a crop plant been demonstrated. A loss in cash value of plants which are grown for their foliage is obvious. These crops include foliage ornamentals, celery (Mus grave et al . , 1976), cabbage, lettuce (Musgrave et al., 1975), and alfalfa (Jensen and Koehler, 1970). The greatest damage by leafminers is often considered to be done to seedlings or young plants which, as a result of weakening, may die or become stunted (McGregor, 1914; Elmore and Ranney, 1954; Adlerz, 1961). Severe damage by leafminers to cantaloups, resulting in complete crop 22 loss (Hills and Taylor, 1951), and to honeydew melon, resulting in reduction in yield and fruit quality (Michelbacher et al . , 1951), have 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 caused by Alternaria blight controlled to varying degrees with fungicides, appeared not to be correlated with tomato yield (Richards, 1947). Defoliation by Xanthomonas vesicatoria (Doidge) Dows. resulted in significant reduction of fruit size (Pohronezny et al . , 1978a). One commercial variety of tomato could withstand considerable foliar damage due to ozone exposure for a long period of time (Oshima et al . , 1975) 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 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 (1970) found a significant yield reduction in greenhouse tomatoes, when all except the top 2 feet of leaves were removed, when compared to plants with only the senescent leaves taken off. Selective removal of over- lapping leaves had no effect on yield. A yield reduction, especially in the largest fruit size categories was found as a result of repeated defoliation at high levels (60% or more) in staked tomatc plants (Jones, 1980). The effects of mechanical defoliation on yield and fruit quality of unstaked tomatoes, as they are grown commercially in Dade County, Florida, have not previously been studied. 23 Actual damage to tomato plants by the leafminer-disease complex occurs gradually, sometimes over a considerable period of time. Exact duplication of this damage is virtually impossible so that simulation by mechanical defoliation may not show the effect of natural defoliation completely (Capinera and Roltsch, 1980). The study presented here was undertaken to determine: (1) the times at which unstaked tomato plants are most sensitive to defoliation, (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 Tomatoes, cv. Walter, were planted in 1977 and 1978 at the University of Florida Agricultural Research and Education Center in Homestead, Dade County, Florida. After metribuzin was incorporated into the soil at a rate of 0.84 kg ai/ha, seedbeds were prepared in groups of seven with their midlines 182 cm apart. Irrigation pipes with frost protection nozzles were set en 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. 24 Immediately after the fumigation, the beds were covered with plastic mulch, and, simultaneously, drip tubing for irrigation was placed approximately 15 cm in the soil below the plastic. Tomato seeds were planted with a seed drill 30 cm apart in the rows. One to two weeks after emerging the seedlings were thinned to one plant per hill. The foliage was removed by cutting the leaves off at the distal end of the petiole with scissors. The fresh leaf weight was consistent- ly found to be highly correlated to the total leaf area (Romshe, 1939). 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. From all but the outer two plants of each plot all mature green and colored fruit was 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 present showed color. The fruit was then graded into USDA grade 1 or 2 after all culled fruit had been removed. These were then sized as extra large, large, medium, small, and very small according to the measurements given in Table 2. The culled fruit was subdivided into several types: misshapen, blemished, sunscalded, decayed, damaged by insects or slugs, and showing gray wall. 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 4 blocks for defoliation at one particular time. Defoliation levels were assigned at random to the subplots within each 25 Table 2. 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 medi urn 58 - 64 142 large 64 - 73 174 extra large 73 213 Source: Marlowe (1978). 26 whole plot (row). Each subplot consisted of 12 plants in the spring crop of 1978, of 22 plants in the fall crop of 1978 and of 17 plants in the spring crop of 1979. Each subplot of plants except for the control group was defoliated only once, and those in each row in a block on a different date. 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 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 (Steel and Torrie, 1960). 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 (FMC 33297) 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 (Bravo^ at a rate of 1.58 kg ai/ha or mancozeb (Dithane M45^ at a rate of 1.34 kg ai/ha. Form-a-Turr^ was applied at a rate of 7.02 1 /ha when bacterial diseases threatened (Pohronezny et al . , 1979). The times of defoliation were: 30 days after planting, 40 days after planting and so on with 10 days intervals up to and including 100 days after planting. The levels of defoliation were: 100%, 80% upper, 80% lower, 50% upper, 60% lower, 40% upper, 40% lower, 20% upper, and 20% lower. Harvesting was done between February 14, 1978, and March 23, 1978. 27 Experiment 2. Fall crop 1978. The tomato seeds were planted on September 13, 1978. A mixture of permethrin (Ambush^ 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-Turr^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%, 80% upper, 80% lower, and 60% upper. 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 yery 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 were: 70 days after planting, 80 days after planting, and 90 days after planting. The levels of defoliation were: 100%, 80% lower, 60% lower, and 40% lower. 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 the 3 blocks. Plants were treated on several days by removing the required percentage of the foliage present on the day of defoliation from the appropriate part of the plants. Each 28 plot consisted of 22 plants. One plot in each block was not mechanically defoliated and functioned as the 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. Experiment 4. Tomato plants were partially defoliated at 30, 50, and 70 days after planting. The levels of defoliation were 60% lower, 40% upper, 40% lower, and 20% upper. Experiment 5. Tomato plants were partially defoliated ewery 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 40% upper, 40% lower, and 20% upper. Gross Revenue Computation The computation of the gross income per hectare was based on the total amount of marketable fruit harvested in the first two pickings in the sizes extra large, large, medium, and small. The prices used for each size are listed in Table 3, and are based on market prices in the season 1978-79 for Dade County, Florida. Results Experiment 1 Defoliation from mid-season on had a striking effect on the fruit set if the defoliation levels were 60% upper, 80% or 100%. In nearly 29 Table 3. Prices in dollars per 13.6 kg box of tomato fruit of the four main size categories and two grades. Grade US DA 1 US DA 2 Size Low Medium High category price price price small 3.00 4.50 8.50 medium 4.00 6.50 12.50 large 5.00 9.00 15.00 extra 1 arge 6.00 10.00 16.00 small 3.00 4.00 6.50 medi urn 4.00 6.00 9.50 large 4.50 7.00 12.50 extra arge 6.00 8.00 12.50 Source: H. H. Bryan, personal communication, 1980. 30 all these cases fruit set was significantly reduced to below that of the control (P < 0.05). The most severe reduction was at the 100% level at the beginning of the last third of the growing season (Table 4). Early defoliation had no significant effect on fruit set. The analyses of all the extra large fruit harvested in both first and second pickings (Tables 5 and 6) and of the large fruit harvested in the second picking only (Table 9), showed that ^ery few treatments resulted in significant yield reductions in these size categories. The variation among the usually small number of fruit in these sizes was large. Combining the yields of the two largest fruit categories also did not reveal any significant reductions (Table 12). Whenever defoliation took place the yield of the large fruit and the combination of the two largest fruit classes showed significant reduction in many of the highest levels of defoliation in the first harvest (Tables 8 and 11). 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. The amount of medium size fruit, especially in the first picking, was affected by defoliation at any level during the last few weeks before harvesting (Table 14). Generally speaking defoliation earlier in the season, of 60% or higher led to serious yield reduction in both first and second pickings (Tables 14 and 15). Plants defoliated 30 days after planting at the three highest levels still showed lush growth at the time of the harvests while leaves of the other plants 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 31 all fruit had been removed, showed a significantly higher value for the plants defoliated early in the season than for the plants in the control (Table 17). No significant difference was found in any of the other times or levels of defoliation tested. The analysis of the gross revenue per hectare (Tables 18 and 19) illustrate the detrimental effect of high levels of defoliation (60% or more) carried out at any time during the season. In the first harvest losses can also be expected to occur if the foliage loss takes place late in the season even at lower levels. The average weight of all marketable fruit was significantly reduced only in the first harvest for the 80% upper and 100% defoliations 30 days after planting. The total weight of all marketable fruit showed a reduction pattern yery similar to that of the gross revenue pattern, the latter based on different prices for the various size categories (compare Tables 18 and 20, and Tables 19 and 21). For both first and second harvests and for all price ranges a highly significant correlation exists between the two variables, total weight and gross revenue. No treatment resulted in significant increases or decreases in the weight of the culled fruit in the first two harvests or in any particular cull category. Only in the third picking there were significantly more misshapen fruit present on plants defoliated at the 80% and 100% levels early in the season (30 and 40 days after planting). In many cases where defoliation significantly reduced the fruit weight, this reduction was more noticeable in the US DA grade 1 fruit than in the US DA grade 2 fruit, especially in the two largest fruit categories (Tables 5, 8 and 11). 32 If the data from the first two harvests are combined (Tables 7, 10, 13 and 16) the impact of mechanical defoliation on the grower's yield can be summarized. It shows that the effect is most pronounced in the plants at first harvest. However, increases in the second harvest tend to compensate for the loss in yield in the first. Experiment 2 In the first harvest the weight of both the extra large (Table 22) and the large fruit (Table 24) was significantly reduced by defoliation in the first month of the season at all levels investigated and in the second month of the season only at the 100% level. No effect at all was noted for defoliation in the last month of the season except a possible yield increase. In the second harvest no significant yield reduction in the extra large fruit was observed (Table 23) while the weight of the large fruit was reduced significantly (Table 25) especially in the very high levels of defoliation (80% or more) in the last two months of the season. The 60% upper defoliation had a significant effect on the USDA grade 1 fruit only, the most severe reduction occurring from defoliation at 50 days after planting. Analysis of the combination of the two largest fruit sizes (Tables 26 and 27) summarize 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 28 and 29) The reduction pattern was very similar to that of the large fruit. Analysis of both the total weight of all marketable fruit and of the gross revenue per hectare show significant reductions at defoliation 33 levels and times at which the weight of the extra large and large fruit was also reduced (Tables 30 and 31; Figures 1 and 2). As in Experiment 1 a very close correlation existed between the total fruit weight and the gross revenue based on different prices for different size categories. From combining the total yields of the first two harvests (Figure 3) it appears that the only significant reduction due to 50% defoliation occurred in plants defoliated 50 days after planting. The average weight of all marketable fruit was significantly reduced only in the first harvest by 100% defoliation of the tomato plants 50 days after planting. In the second harvest no significant reductions 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 present on plants defoliated 15 days before the first harvest at the 30% and 100% levels. Defoliation at 80 days after planting also resulted in more decaying fruit when 80% or more of the foliage was removed from the plants. Experiment 3 Since only late-season defoliations could be examined for effects on yield and fruit quality, differences in reduction patterns as found in the first two experiments could not be verified. In fact, analysis of the weight of the various fruit sizes, total weight, and gross revenue revealed only very few significant reductions when compared to the control . 34 No significant differences in the weight of the extra large fruit was detected (Figure 4). No extra large fruit was harvested in the second picking. The weight of the large fruit was only reduced significantly by defoliating plants 80 days after planting at the 100% level in the first picking, while in the second picking the reduction was only significant when the plants were completely defoliated 90 days after planting (Figure 5). The latter was also the case for the weight of the medium size fruit in the second harvest (Figure 6). 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 7). Both the weight of all marketable fruit (Figures 8 and 9) and the gross revenue per hectare (Tables 32 and 33) were signif- icantly reduced by 100% defoliation at 80 or 90 days after planting. Total weight of the culled fruit was not significantly different between any of the treatments and the control. The weight of the culled 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. 35 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. Analysis of all extra large fruit in the first harvest showed that the repeated removal of 40% from the upper part and 60% from the lower part of the foliage of the tomato plants had the same effect on yield in this fruit size. Removal of 40% of the foliage starting at soil level also reduced the yield, but not as severely (Figure 10). In the second harvest significant differences in the yield of extra large fruit also occurred (Figure 10) but because of the low total yield in this size category its effect on the overall fruit yield in this harvest was negligible (Figure 14). The yield of large fruit in the first harvest was also signifi- cantly reduced at some defoliation levels (Figure 11) but not as severely as that of the extra large fruit. The effect of defoliation on the yield in the two largest size categories is summarized in Figure 12. Reduction in the weight of the medium size fruit in the first (Figure 13) had only a minimal effect on the total yield (Figure 14). In the second picking the increase in the weight of medium size fruit and large fruit accounted for the significant increase of the total yield. The total yield of the first two harvests was not significantly reduced by defoliation at any level (Figure 15) while the combined weight of all extra large and large fruit was significantly reduced only at the 60% defoliation level. 36 Experiment 5 Frequent defoliation of tomato plants resulted in a reduction of the yield of extra large fruit at all levels tested (Figure 16) and of the large fruit at the 40% level (Figure 17) in the first harvest only. Reduction was evident in all defoliation levels when the two largest size categories were combined for analysis (Figure 18). The yield of the medium size fruit was only significantly reduced as a result of removal of 40% of the foliage from the upper part of the plants (Figure 19). In no size category was a yield reduction observed in the second harvest. The total yield loss as a result of repeated defoliation (Figure 20) 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 21). Discussion Defoliation of unstaked tomato plants revealed a changing sensitivity to this type of damage in the course of their development as was demonstrated for potato by Skuhravy (1968) and sugarbeet by Capinera (1979). 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CD ro ID -C ■X -X ■X -X -X «d- r-~ en * >* ■X -X * ■X -X * CO 00 <-H oo p-~ cm 59** 10 86** ■x -x -X * * * p^ ld csj t-H cm en CM CO O CM CO ■X LO O LO CM «3- 00 ■X -X LO tO •— 1 oo oo o 00 LO ■53- oo to CO O O P^ i— 1 «3" 1 O O l-H o co en to en p~ CO CO CO 03OH en «3- r^ «3- en to oo to <^- OO CM LO CO to r^. oo lo "=}■ CM "=!■ r- o oo CO <— I •— I ■X to en pv. to uo oo ■X en o i— i rtlllO tO Tf CM r~~ co uo O-HLfl co en co O 00 O p-^ cn co en to co to U0 LD CO OO CO en oo to U0 <3- LO uo uo uo tO CM LO p^ lo to en o oo <=*■ co to to co en o to co cm en to en r-» co +j t— ra CO •■- > -X -X to r^ uo CO O CO ■X p-. uo cn 00 to CM tO CM 0O r-i <=T O en en en «*■ r«s «* i — en to t— 1 to LO oo i— i oo P"- >— 1 CM O to i— i oo r-~ lo LO LOCO OlsfO O CO o en to co en co tj- co p^ co co cm en «=j- r^ lo oo o en to "^- en •-1 CM + i—i CM + 57 ■M rO C i— CU O O S- S_ +J CJ c Q. O CM Lf> O CO CM cm co en cm cn *f en CO CO <-< *d- r^ «3- LO <3- r^ (£> U3 LT> UD vo * * O CO X -X CM <3- ■X -X -X -X * OWN O CM Uf) HCIO «3- en CM ■3- <*■ LT5 «3" CO CO CO * * -X cm O r»~ r»~ i— i o * * * l— t CM i-H CTl -X -X to ■X -X -X ■X -X -X co r--. co tn cnio en *&■ «3- cr> co cn CM CO CO i— i i— i i — i <— 1 I— 1 r— 1 -X -X CO CTi CO O lO 1J3 ■X -X -X iocvuo O 00 o •X -X co co cn CM CM CO ■X -X -X i-H LO CM 1^ CTI "3" re CD 2 •r- > o i— CU r— O r— <4- "-< CJ O Q CO -X -X -X C7> CTi Ol CM CM r~~ ■X X X X ■X ■X -X X -X X -X X X CM LT) < 1 o *d- ^ cr, CO r- 1 CT> CO o r~- CO co >-" CO co ^r cn CM ■X -X -X •X -X -X LD t^. CM VO -U" CO lO r-H CTI CXI CO CM r»» <& o ■X -X -X IDOl/) 0DH| — rxHN LT> CO CXl HfON UD r^ u3 NHfO i-H CO CM •i— co Q. •!- -i- 58 -a r— CD 0) C3VQ « " >> +■> fO C r- c CU o re o s- OJ S- 4-> E Ol c Q. O LO c o -l-> . 0) C CO S -o > +J -r- 4- -C O 4-> c <+- o O +-> +-> rri c/> •i — QJ > O L_ <+- IT! CL) -C -o T7 <+- C O O o 0J a> (_) I/) -o a) **- CT LO i-H CM CM -3" LO Ln 00 r-. LO o 1— 1 r% oo oo O O LO O LO CM r— 1 IX) o .—i LO "=T CO LO i-H P-. r«s. *j- 1 — «3 H O CM to «3" Lf) Lf) o CM LO i-H LO CT LO LO LO O CTl O CT O CT O CO CT CJ^ CO CO p^ oo r-s CT r-» oo .—1 i—l i— I t—l * * *d- --< *i- «=!- oo CT 00 o ^r CT CTi r^ CT CM onin CM LO r^. i—l CM o r-» 0O CO oo «3- CT o i—l CT en >=j- vo oo lo CT «d- lo Lf) CM CO O oo 00 1 — 1—1 00 "* JlrtO p-* co p-~ O lo a) en lo co LO 1 — 1 CO 00 "3" LO i—l r— 1 * * i—i 1— 1 CO O P^ *? H LO O "* o ■—I CM o LO Lf) «3- on LO 00 >?lOH lo to CO O X) ■* co oo Lf) CT CM LO 1— ( o o LO ■— 1 CT *3- CO LO ^- ^J" CT on ,_, Lf) » p^ CO LO r-. <* LO If) ■K -X LO 00 LO 0O CO CT * * 0O o o LO ■— 1 LO * CO CT CM o r-» o O CT CO cohn LO O CT ^3" 00 CT .— i p-^ ^> co i^cm OO O i— I lo r^ lo CO CO CO LO «3" LO CM «3- LT ■3- P^ o ONOD CT CO CO P-~ LO ■— i O CT O CT LO CO r- LO lo ■—I CM + i-H CM + i—l CM + i—l CM (TJ 0) ■r- > <— a> o r— 59 S- i_ +-> ra CD to CO r-> CT> CM *3" * * * <=f co en i— i CM i— I * * * * OC0N tO CM CTl to CO rv O "St" CM LT) Lf) LO r«- «3- lo un lo lo * * CO CO CM 60** 85 99** 10** 66* 66** CO tO IXJ rv «a- o co to tn r-« CM CTl CM LT) CO * * CO «— • to CO CM O * * * Mcors en to co * * -x CO CM tO «=a- r^ o * * * * * „ V to i- 1 CO en en n- en lo en CM CM CTl LO i—4 iv to co en oo 0) Q. to to to LTI "3" "* IONH T3 S- to to to n iv in CM LT) <* i * * * * oo n oco* i—4 CM CO CO CO rv ZD rv i — en O Lf) CO ^- CM ^1- .« -a cu cm i — en ocot co o to en 4-» tn co to en tv co co co tn 03 •i— in +-> i— t3 cu •r- > r— CU a. -i- •!- A 60 l/l CTi +J , — t c * 4- O Q. O C +-> s_ rt3 u c +-> O > IT3 S- •r- 03 co c D_ O c o O) E -O +J 1 — ra eu aj t- s- >> * ■X * * * 0OCX1N LO cr> cm i — n CO LO n. cm CO LO CO <*■ <* O co a CTi CM LO CO n CO LO i-H o o o en n co co n o a-> CM to «* Sf =3- *r . — i CO lo n CM .— 1 N n N LO ■X * n n n n * n LO LO LO n n n n lo * * n * LO CM CO >3- en o en LO en CO LO ■=r .-h en en CM n cn CO co in LO n n LO n ^H *|- 1 — 1 n LO «d- LO N CO N lo n lo n LO iX) in LO n LO en n lo n co N lo n i-H LO CO en rr en O CM en CO *3- T— 1 ,— 1 O o CO _l CM COO^t CM CO CO CO CM n CO en LO n LO CO n * CM CO O CM O 00 «* CM O en ^r co lvO«3 * n co CO NOO * * * * O CO CM LO LO O * * * * en o o en lo en "3- «* LO O LO 00 NNO en co en i— ( n «^- en n co en i— i lo COLON LO "* LO LO LO LO OOOH lo n lo CO o o co n co I- 1 LO «* «3- CM "3" co o en LO r— 1 t— 1 O n r^ LO CM CO LO CO r-H LO CO «3- CO O CM CM LO LO * LO LO i— t HOLO LO O CO en en en •* n lo en n co r-H LO CO en en en ^ LO LO CO CO CO CO CO CO CONN en >3- i— i LONN CO N CO CO O CO n >3- en CM CO LO LO LO o ,-H o .-h o >=r co en en o CO "3- "3- N o o n *s- en O LO CM co o en t— 1 O LO co en co co cm en cm n en O "3" N en co co LO 00 1 — CO CO CO co ^- CO IN CO IN .—I CM + i— I CM 61 4- a. o S- 0) 0) cao +J i 5- +-> rt5 OJ £= T3 O. O O) 01 E-O •T— +-> i — re 0) o CD •<- 4- i- >> cu +-> ■o s- 4- OJ O o ■— <_> +-> r— i— — I CO LO lo co «3- cn co o IfilO ID «* "3- >=i- r-l <* OJ LO LO LO * -X Cn «* LO CO ^H CO -X -X -K -X -X -X Oino ■X * -X * * * ld cn r— 1 LO CO CT> CO --• co N00O V£) O LT) LO cn oj r~ co to r-» o "vf CO to lo . — i to to O CO CM CO OJ -x * * to en i — i <— i CO o * lO O C\J O * ■X o to ■X * 1 — 1 LO ■X -X ■X -X ■^- CM >=r O lo co LO to cn lo to l£) CO to o LO CO CM cn to «3- co •X -x O to 00 CM ■x <* * -X ■vf to r- cn o co -X ■X cn -X ■X co cn cn co cn o <3- r-» cn LO to CO CO to cn to "3" i— 1 CM CO CO to 1 — 1 r—i en o r~- T 1 en <3- LO •3- r~- <—i r^ LO CO o « — 1 CO en LO 1 — ■3- LO LO *t O P-» co to «=r ■X -X ■X -X LO CM O CO •X •X I— 1 CM ■X -X ■X -X LO to rH OJ ■X -X cn -X ■X LO •X -X ■X -X CM <-< O O CO o CO LO <3- ■3- CO CO LO *d" O LO en CO CO I— 1 ■X -X •X -X <* *}• o 14** 54** 33** -X -x -x -X * -X r»s ^- o CO CM LO Ln r»- "* to to LO CM CM LO LO CM LO CO CM r^ lo CM CM o co to to =3- 62 Table 17. 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. Defoliation Mean fresh weight per plant (in grams )a' Time of defoliation (in days after planting) lever 30 60 100 80% lower 80% upper 100% 11062* 8080 6928 10960* 7100 8175 14177** 7595 7785 aMean fresh weight per control plant: 8545 g. Weight is significantly different from the control if indicated by for P < 0.05 or by ** for P < 0.01. cFor an explanation of the defoliation level codes see page 26. 63 Table 18. Gross .revenue in dollars per hectare of 'Walter' tomatoes based on all marketable fruit of sizes extra large through small. Influence of defoliation on the first harvest of the spring crop of 1978. Defoliation level0 Price rangec Gross revenue in dollars per hectare Time of defoliation (in days after planting) 30 40 50 20% lower low 8082.09 6550.75 5324.03 medium 12637.24 10303.40 8493.80 high 21392.33 17327.15 14268.75 20% upper low 6545.31 6193.58 3872.43 medium 10280.84 9754.46 6281.72 high 17327.81 16428.61 10748.39 40% lower low 5382.35 4579.86 6870.04 medium 8378.81 7279.11 10919.89 high 14092.30 12251.89 18362.76 40% upper low 4756.31 6316.15 4511.49 medium 7543.69 10130.75 7076.46 high 12751.90 17052.51 11725.68 60% lower low 5453.36 4049.70 5620.91 medium 8520.16 6440.70 8852.95 high 14178.30 10791.39 14785.40 60% upper low 3991.70 5667.20 5267.03 medium 6143.33 9069.60 8346.68 high 10387.59 15295.96 14047.32 80% lower low 4358.11 3854.30 6331.63 medium 6787.66 6185.50 10011.80 high 9246.99* 10316.42 16681.33 80% upper low 2348.83** 2951.32** 5259.78 medium 3619.87** 4644.44** 8123.45 high 6215.82** 7791.31** 13707.45 100% low 805.63** 1397.73** 3517.23* medi urn 1242.04** 2236.14** 5362.91* high 2126.91** 3722.67** 8967.95* A significant difference from the control is indicated by * for P < 0.05 or by ** for P < 0.01. ror an explanation of the defoliation level codes see page 26. 64 Table 18. Extended Gross revenue in dollars per hectare3 Time of defol 'ation (in days after planting^ 60 70 80 90 100 6173.47 6009.88 6039.37 2433.01** 3177.35* 9767.64 9644.90 9527.27 3643.43** 4884.31** 16265.67 16276.05 15813.27 6048.10** 8159.86** 6147.28 5318.10 6807.10 3296.79* 2662.18** 9617.88 8434.99 10794.19 5132.76* 4083.64** 16063.85 14265.29 18167.70 8572.06* 6791.28** 5095.03 5408.71 5311.34 2788.05** 3964.52 8046.67 8472.88 8200.71 4222.35** 6119.93 13434.95 14299.88 13663.95 7027.70** 10155.79 4591.06 4845.43 4057.60 3680.82 2952.63** 7398.22 7845.84 6443.66 5693.40* 4537.35** 12597.86 13281.38 10778.38 9493.99* 7474.33** 5419.59 2693.48** 4990.19 4065.18 5113.31 8656.90 4081.66** 7772.03 6541.85 8183.41 14481.44 6870.53** 13029.51 10983.16 13747.98 4337.84 4331.91 2842.58** 3612.12 4244.26 7106.12 6742.85 4417.75** 5712.84 6678.10 12011.36 11282.84 7327.38** 9548.36* 11109.36 2665.81** 2128.23** 3211.95* 3348.36* 3748.70 4296.49** 3315.41** 4963.23* 5350.39* 5976.93 7263.29** 5608.72** 8288.86** 9150.98* 9943.92 2542.74** 3098.60* 2298.74** 2725.11** 2931.05** 4154.81** 4803.75** 3598.78** 4259.09** 4535.05** 7114.36** 8036.95** 6025.53** 7187.50** 7599.87** 1923.61** 1491.64** 1466.60** 2522.31** 2880.97** 3087.23** 2285.07** 2297.76** 4051.18** 4466.68** 5310.85** 3845.90** 3790.05** 6796.89** 7453.91** Prices used in the computations are given in Table 3. Note: Gross revenue per hectare of the control plants was for the low price range, $6194.11, for the medium range, $9829.29, and for the hi ah range, $16607.44 65 Table 19. Gross revenue in dollars per hectare of 'Walter' tomatoes based on all marketable fruit of sizes extra large through small. Influence of defoliation on the second harvest of the spring crop of 1978. Price - range Gross revenue in dollars per hectare Defoliation level Time of defoliation (in days after planting) 30 40 50 20% lower low medium high 4563.55 7104.97 12227.51 5193.22 8039.75 13900.53 6543.17 10308.02 17950.72 20% upper low medium high 4059.58 6412.53 11250.22 5135.56 8048.32 13881.75 5833.43 9111.45 16003.55 40% lower low medi urn high 7001.67 11108.37 19569.22 5337.04 8376.83 14530.70 6090.78 9568.95 16476.06 40% upper low medi urn high 5774.95 9103.87 15836.17 5781.54 9070.75 15851.00 5732.94 9001.06 15687.90 60% lower low medium high 7004.47 11105.89 19362.29 4477.72 6946.81 12010.86 5343.14 8374.69 14674.69 60% upper low medium high 3737.50* 5796.53* 10259.42* 5059.28 8021.46 14072.86 3982.64 6185.83 10740.81 80% lower low medium high 2570.91** 3989.40** 6938.90** 3413.60* 5286.63** 9039.12** 6723.57 10580.51 18171.65 80% upper low medium high 2426.76** 3763.36** 6585.18** 3676.05* 5729.15* 9997.80* 1704.49** 2602.21** 4614.78** 100% low medium high 1595.76** 2469.10** 4322.69** 3260.88** 5088.44** 8866.79** 2719.68** 4171.45** 7113.04** A significant difference from the control is indicated by * for P < 0.05 or by ** for P < 0.01. !For an explanation of the defoliation level codes see page 26. 66 Table 19. Extended Gross revenue in dollars per hectare Time of defoliation (in days after plantir ig) 60 70 80 90 100 5998.51 5101.78 5819.10 7340.06 6273.81 9313.43 8080.12 9117.71 11550.22 9846.72 16178.68 14145.02 15908.33 19939.24 17153.50 6105.44 5359.28 3796.15 4976.57 6812.87 9500.42 8417.19 5738.87* 7778.30 10674.09 16398.13 14726.59 9851.99* 13439.07 18326.84 6074.29 4353.30 5855.84 6083.85 6255.19 9670.44 8468.43 9186.73 9729.58 9832.39 16904.73 14808.63 15841.28 17019.07 17188.43 5612.67 5136.47 5752.87 4440.31 5391.91 8740.10 8248.49 9039.45 6935.28 8474.69 15059.05 14323.77 15933.21 12216.80 14736.47 5828.49 5634.25 4310.82 5208.09 5128.97 9158.40 9012.27 6779.92 8053.43 7931.51 16080.99 15584.60 12185.33 13803.00 13724.42 5720.42 4041.95 5883.35 4826.49 5462.75 9020.13 6392.43 9293.65 7786.70 8576.18 15500.08 10943.62 16007.51 13607.61 15051.30 4547.24 4602.10 5306.89 3023.64** 4784.15 7174.33 7225.73 8399.23 4585.30** 7433.97 12249.09 12505.11 14574.35 7838.43** 12846.14 5702.62 3233.86** 4486.12 3425.79* 3267.80** 8980.14 4956.31** 7044.50 5382.52** 5081.03** 15615.57 8444.54** 12366.56 9210.46** 8841.09** 3101.73** 2773.88** 2835.33** 2289.19** 3533.70* 4760.92** 4247.23** 4346.08** 3591.53** 5538.86* 8075.67** 7173.83** 7478.12** 6094.89** 9654.95* "Prices used in the compu tations are given in Table 3. Note: Gross revenue per hectare of the control plants was for the low price range, S6286.20, for the medium range, S9798.74, and for the high range, $17064.17. 67 3 -r- i. 4- 4-> a; 3 r— S_ .a 4- «3 O 3 T3 'a. >> ? +J > +-> in 1 — = ra 00 n +J r^ +-> o cn +-> i — i s_ CD 4- a; JZ O +j 4-> r— a. ra -o o O r— 4-3 4- 3 x: +j i — en i/) 4- -i- s_ C CJ -r- o o I— 1 o CD O CO CD C +J c 4- (O (/) >> CO x> c o •r— to * ' c o +J 03 •F— O o 4- in CU ■a 4- o cu £ I— o ^f o m | * -te ■X -X •X -X co r~. xi O CMCM CO O CO mom CO O CO CO O CO CD «3- -3- r— 1 O T— 1 ■g- ro n *r >— i x> co *i- i^. i-x o r-x CO CT> CO oaicn en cm i— i CO CO r- 1 CO oo to CO CO to <^- IX) «* «d- U1HN «d" IX) r~. co to <— < r** * -X ■X ■X * * ■X ■X -X * ■X rorso oo o co co X) co LT) O IX) co r- o co to co 00 C\J ■— 1 i— 1 CM CO MinN OiOON en cm cm ■3- >3- CO to to co <— 1 i— < CM CO o CO co o en CM o co ix> cn >^- co «=f X) i— 1 lO «3" i— 1 X) IX) CM 1^* to «— * P"> lo to CO X) CO o o o ix) ix) o o txi lo LO cm r-s ix) ix) o co .— i to co >— i *d- tow to >sf o cn CO CM i— H CM x}- cm en i— i co ix) co t— 1 O i— 1 co lo en a) co r-» ^r co r-». en o O H co f-H en to to (^. CO *3- <— 1 IX) O IX) LO en co cm MNO CO IX) CO *NIV >* CO CM cn o co o co >d- cn co co cm to co CO o o o Ncom <=i- en «3- oo en O r-s r^ o en cn to co ^a- cn o CO IX) co to to co co r-. i— i CO IX) co NOCO tO rHN co i— i cn co lo co o co co r~. to co r-x co to o lo CO CM IX) rNCTun O i-i o o o to <3- o IX) CM 00 co r~~ X) r-~. lo co co r-x r-i ^- HtO O X) IX) IX) to i— i cm o co co i— i cn CO CM IX) ■3" CO CM cn co co CO CM IX) co to «d- r^. co i— i to «— * co IX) O IX) t-t co cn cn (■--> to CO IX) co cn i— i O cm co H co cn CONO o ix) lo o r-» r»* O CM CM O CM CM CO IX) CO ■* ^f cn COHrf o r->. r>« co i— i cn to <— i r~» to CM CO co to cn 1 — CO IX) CO 1 — o cn to ix) ix) CM to CO CO CM IX) CO CO CO CM O cn X) X) ix) cn m X) cm r-- O cn cn co cn cnj x) x) o x) <^- o cn co co 68 oo cm lo mom CO O CO o ^orvcn «3- o ■«*■ LO l~N CM CO en LO CM CO CM O oo en lo LO • r— Lf)rHl£| «3- r-l LO oo >* 3 * -X * * * * oo o oo CO O CO UO LO o i — en lo vo r~ oo i— 1 OO LO IOHS coitus stiflO oo r— i tt «3- lo CM OO U1 MN Lf) Lf) O cm un oo CO cm o *mo r-» tj- cm > >> OO CM LO O LO LO O LO LO o o o r-» r-» >^j- ^j- LO co cm o LO CO LO CM i— I "5T * * o o o LO LO o OO LO CO LO OO CO en «3- ■^r •-*Or—< LO OO CO LD LO OO lo >^r o en en CO en LO LO co r^ lo OO LO CO co cm o LO <"H CO en oo cm CO f^. 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Q to _c S= S- ro +-> re U +J 4- Q-r— c o CD O (0 E T3 ■4-> 4- -t-> i — n3 ro 0) E cd (U •!- o .c s- >> o O o +-> cd 03 1/1 CD O -c 4- +j 0) O c ^ CO CO LT) >— I O C\J O CO LT) t-i O CM CO re CD ■i- > — CD O r— in 'r~ v O S- ■r- o >- 4- 73 a> o s- -t-> +J 4- C o CI) — ■o +-> CO CI) aj s_ >> S_ 4- 0) O 4- CO o sz O i/> •r- S_ +-> •!- rO 4- 4- O +-> 0) 3 (J i- C 4- aj 3 cu i— a> 4- s_ C ra ra CD •1- > i— ra 00 C i— i— i S- +-> CD C C M- Q. O o o CJ rt3 i/l Q- a> ■*-> O IS> -C C s_ 03 •+-> (O <_> f — +J <+- a.!— c o a> O IT* E -a +J M- +-> i— tO > +-> +-> +J n3 ai r— CD r*. oo ^t «=r ro CTi oo m CO *3" CM LD oo en co ocom noco CI CO CM nwo HOJN r^. >3- oo * * CM *3- i£> r~ >^- cm «3- o o r-» o r-N. * * * * r*~ en r-^ r-. co en oo en en m *3- i — i— • O CM oo un in son en en ix) CM CM CO CM •— 1 00 CO CT> 0O •i- o ■a i/l • o > ■a q. > 4- 4- o £= O "3 0) d) Q. cno E O 03 •> S- +-> (O dj 0) "3 +-> -C O) c +-> 00 J= 03 03 +-> r- 4- Q. 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OJ 3 C1J C7> u_ i. ai ■!- s- >> ix) ix> co o oo en ■x * in rv io «^" X3 >-< CT1 LD CO ^t LD IX) -K * at ci o roion * * O O LD CO LD ID ■K * «3" «=f «-* ocoo * X) XJ ■it CM X3 r-^ cri CM X) CM O X) CO CO "=f IX) cm XJ oo IX) X) <* CO OO IX) IX) CM i — ro X) ix) r-- XJ i— I r— O) O r— •T- V T3 Q_ 77 -a 0) in 10 i— i cm >— I CM m rH CO r-. oi in 0) oo -t-> c^ C i— OJ o u s- i- 4J O 4- o 10 4-> Q. C O (T3 S- i— U Q. O r- (0 4- E O OJ 4-> 4- C O CU E T3 4-> .— fO <1J O) >r- i— 0) O J= 4- +J co co O CO >— 1 in r~- l~~ CO ro O O C\J CO CM •^J- CO O CM CO ^H CO CM CM in r>» un to io 10 •f- T3 +-> r— r— CJ •i- o O 78 CO E i— OJ r> cu o -c en CJ S- +-> i— • S- -I-) o oo _c £Z i- ns +-> rt3 4- a..— C O OJ O n3 e -a -M 4- 4-> i— > +J -(-> +-> - 4- s_ S- O OJ aj Q. +-> +J i — CO -o IT3 0) 3 > OJ c cr O o (.j +J a; ra 1/1 (i) o .c 4- +j ■K * * -X cx> co «-i **■ CXl CM ■X co en <3- en CM * * r^ r-~ en <— i lo co * i— 1 CO CO r^ cm * * co *3- m lo en en o Ln in .—1 r-tN. C\J ^j- ^a- rj- in H CO 'X> <* r«. co o n Ln >^- * LT> X) * CO r-i en t— ( ■X -X -X Ln cm r-. oo r-- n * en -X CO ^H r~» Ln ■X -X en *$■ <3- r-. r— 1 I— 1 O CM Ln o 1 — ID N Ln Ln Ln ro <— i Ln CXl CT> rH <3- Ln lo ■X -X •i- o CO o 79 « (/) E i- (/) C rt3 o -Q 4-> LO OS 0) •i — O i — +-> o rri <+- K fl) O -a rn , — +j i — <5 ffl QJ != x: LO s- c (U TO Q. 3 r~. I— ( LO NO* * C\J CM ix) en un o r-s o * LO i— « r-.r--.LO en * ^J- LO i— I ai no |-~ i— I CM 00 CM to IX) I — I — "St- CO <— I * * r-- CM en cm oo Ln«D o or~-.ro * lo r- 1 r— i cr> oo conn OO CO o CM «3" CO couno IDNH 1X5 CO * CM ■=}■ I — COO* cm o r-» co * r-- oo 1X5 o en ix> oo en * * lo en en OO LT5 en r--. r-. ix) en r-» * o cm co oo LO oo * cm CM o en o * lo uo oo lo en 00 CM i— I LO LO LO r--. uo co cm * rv. I — IX) * r^- <— i lo o lo) en cm oo LO LO IX) LO oo en oo IX) LO CD *■ r~cM CM IX) LO I--. 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Gross revenue in dollars per hectare of 'Walter' tomatoes based on all marketable fruit of sizes extra large through small. Influence of defoliation on the first harvest of the spring crop of 1979. Gross revenue in dollars per hectarec Time of defoliation (in days after planting) Defoliation level Price - range 70 80 90 40% lower low 6669.04 5261.75 3866.00 medi urn 10782.49 8657.34 6316.70 high 18404.99 14862.78 11009.63 60% lower low 5446.27 4878.66 5231.33 medium 8864.27 7990.99 8598.03 high 15208.09 13941.17 14916.82 80% lower low 4021.30 4737.85 4622.42 medium 6603.69 7739.91 7412.39 high 11543.96 13356.20 12663.16 100% low 3684.56 3101.79* 3667.31 medi urn 6050.79 4981.35* 5962.71 high 10528.45 8599.68* 10165.67 A significant difference from the control is indicated by * for P < 0.05 or by ** for P < 0.01. For an explanation of the defoliation level codes see page 26. cPrices used in the computations are given in Table 3. Note: Gross revenue per hectare for the control plants was for the low price range, $5246.52, for the medium range, $8575.55, and for the high range, $14728.45. 96 Table 33. Gross revenue in dollars per hectare of 'Walter' tomatoes based on all marketable fruit of sizes extra large through small. Influence of defoliation on the second harvest of the spring crop of 1979. Price range Gross revenue in dollars per hectare Defoliation level Time of defoliat- on (in days after planting) 70 80 90 40% lower low medi urn high 3049.83 4862.73 8683.05 1595.98 2522.09 4505.01 1818.72 2881.90 5171.14 60% lower low medi urn high 1972.38 3108.48 5658.80 1950.85 3088.61 5558.63 1645.29 2590.07 4602.54 80% lower low medi urn high 1876.49 3026.00 5460.66 1727.45 2701.55 4834.29 1474.94 2296.16 4082.92 100% low medium high 1812.90 2876.96 5165.98 1613.11 2552.07 4533.45 653.07** 1023.86** 1815.34** A significant difference from the control is indicated by * for P < 0.05 or by ** for P < 0.01. For an explanation of the defoliation level codes see page 26. cPrices used in the computations are given in Table 3. Note: Gross revenue per hectare for the control plants was for the low price range, $2152.65, for the medium range, $3430.95, and for the high range, $6181.35. 97 z < -» 200 X o HI £ 100 5 I first harvest I I | 1 I I iJ li I I USOA grade 2 USDA grod» 1 second harvest ab ab EL 0 20U 401 40U 601 0 20U 40L 40U SOL DEFOLIATION LEVEL Figure 10. Influence of repeated defoliation of 'Walter' tomato plants on the mean yield of all extra large fruit (3 defoliations) Columns not marked by the same letter represent significantly different weights (P < 0.05), Duncan's multiple range test. For an explanation of the defoliation level codes see page 26 . 98 _ 400 z ae 300 r 2 200 u j» 5 j* 100 n I i i I i first harvest ab «* 1^ Hill i 1 i 1 1 i 1 1 il if i i | illil I I USDA grad* 2 USOA grad* 1 sscond harvest m 1 1 i 1 i 1 11^ '^ ^ ^ 111 ill 111 I 1 i 1 1 0 20U 40L 40U SOI 0 20U 40L 40U 601 DEFOLIATION LEVEL Figure 11. Influence of repeated defoliation of 'Walter1 tomato plants on the mean yield of all large fruit (3 defoliations). Columns not marked by the same letter represent significantly different weights (P < 0.05), Duncan's multiple range test. For an explanation of the defoliation level codes see page 26. 99 800 _ 500 z < 1 I first harvest I I !l be s. be I I I I I USD* 9 rod. 2 USOA grad* 1 second harvest ,1 ££ 1 M II 20U 40L 40U SOL 40L 40U SOL DEFOLIATION LEVEL Figure 12. Influence of repeated defoliation of 'Waiter' 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. For an explanation of the defoliation level codes see page 26 . 100 z 19 r- 150 I I USOA grade 7 USD* grad* 1 first harvest 1 1 ab I second harvest ab si u I I ab I I I i i 111 I ab 1. 0 20U 401 40U SOL 0 20U 40L 40U SOL DEFOLIATION LEVEL Figure 13. Influence of repeated defoliation of 'Walter' tomato plants on the mean yield of all medium sized fruit (3 defoliations). Columns not marked by the same letter represent significantly different weights (P < 0.05), Duncan's multiple range test. For an explanation of the defoliation level codes see page 26 . 101 first harvest 900 500 200 - small FRUIT 1 I medium SIZES IHI3 large H|llll extra large second harvest b S8 b nd I ab ab 0 20U 401 40U SOL 0 20U 40L 40U 60 L DEFOLIATION LEVEL Figure 14. Influence of repeated defoliation of 'Walter' tomato plants on the mean total yield of all marketable fruit (3 defoliations] Columns not marked by the same letter represent significantly different weights (P < 0.05), Duncan's multiple range test. For an explanation of the defoliation level codes see page 26. 102 1250 1000 750 Bsi small FRUIT I I medium SIZES g^ large lllllll extra large 0% 20% upper 40% 40% upper DEFOLIATION LEVEL Figure 15. Influence of repeated defoliation of 'Walter' tomato plants on the mean total yield of all marketable fruit in the first two harvests (3 defoliations). Columns not marked by the same letter represent significantly different weights (P < 0.05), Duncan's multiple range test. For an explanation of the defoliation level codes see page 26 , 103 150 Z o M 100 5 50 first harvest I r n 1 i! iJ 11 I I USDA grads 2 USDA grad. 1 second harvest 20U 401 40U 0 20U 401 40U DEFOLIATION LEVEL Figure 16. Influence of repeated defoliation of 'Walter' tomato plants on the mean yield of all extra large fruit (6 defoliations). Columns not marked by the same letter represent significantly different weights (P < 0.05), Duncan's multiple range test. For an explanation of the defoliation level codes see page 26 . 104 m 500 — at 300 - 2 200 3 5 100 first harvest i i i afa 1 I I 11 I 1 USD* grad*2 k\\\N USOA grade 1 second harvest 20U 401 40U 0 20U 40L 40U DEFOLIATION LEVEL Figure 17. Influence of repeated defoliation of 'Walter' tomato plants on the mean yield of all large fruit (6 defoliations). Columns not marked by the same letter represent significantly different weights (P < 0.05), Duncan's multiple range test. For an explanation of the defoliation level codes see page 26. 105 200 50 Figure 18. I I USOA grid. J SNSSJ USDA grod* 1 first harvest ab „ ab I 1 ill second harvest In I I ill i i ill ^ 0 20U 401 40U DEFOLIATION LEVEL 0 20U 401 40U Influence of repeated defoliation of 'Walter' tomato plants on the mean yield of all medium sized fruit (6 defoliations). Columns not marked by the same letter represent significantly different weights (P < 0.05' Duncan's multiple range test. For an explanation of the defoliation level codes see page 26 . 106 700 s 5 soo w 3» _C 2 SOO < a. at 2* ^00 first harvest 1 | I I | i_k if I 1 USDA grad*2 E5g< b — a ¥o°: "" |«J>! b Z 4 second harvest w ffl X at X H" X soo 400 ■» >23l WW3 >2a£ b a a 1 a 3 2 ;;<; J3°3: $$ Ul 'o°oc 5 300 M II ijcg: '"A; a _ 5 w M0- ' ae j'o0 330° iD5:: *. 200 100 i W W: s 53? ■™ ~y:r :,'•:; : r: . R^-: HI ill 1111 llll &a bii 20U 401 40U 20U 40L 40U DEFOLIATION LEVEL Figure 20. Influence of repeated defoliation of 'Walter' tomato plants on the mean total yield of all marketable fruit (6 defoliations). Columns not marked by the same letter represent significantly different weights (P < 0.05), Duncan's multiple range test. For an explanation of the defoliation level codes see page 26 . 108 1000 _ 750 z < Q| small FRUIT I I medium SIZES E&m large IIIIHI extra large fit 0% 20% upper 40% 40% upper Figure 21. DEFOLIATION LEVEL Influence of repeated defoliation of 'Walter1 tomato plants on the mean total yield of all marketable fruit in the first two harvests (6 defoliations). Columns not marked by the same letter represent significantly different weights (P < 0.05), Duncan's multiple range test. For an explanation of the defoliation level codes see page 26. 109 development, seriously slowed its 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 (1935) postulated that the ultimate fruit size is determined early in its 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 mobilization to growing fruit. Defoliation of the tomato plants at the lower levels (20% to 60% near the soil level) has little, if any, effect on fruit set, development or quality, especially when it occurs in the first two months of the season. It appears that the foliage remaining on the plant is capable of synthesizing sufficient amounts of nutrients necessary for the normal development of the fruit. Since the foliage 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 even beyond the compensation point, using more photosynthate than they produce. The upper 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 (Acock et al . , 1973), 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 resulting in an increase of 30% to 50% of the exported photosynthates (Khan and Sagar, 1969). 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 development are, no therefore, well able to compensate for the loss of photosynthetically 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 process, whereas under normal conditions division and enlargement of the pericarp cells still would be the most important activities in the fruit. This temperature effect will have an especially profound effect when the ripening process is well under way, towards the end of the season and the plants1 energy production is almost entirely directed toward reproductive development. Replacement of vegetation removed is then negligible and damage to the fruit by sunscald and decay becomes more likely. Sunscald may not occur if defoliation 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 (Marr and Hillyer, 1968). On the other hand, exposure may mean temperature increases to levels where fruit set may be affected (Marlowe, 1977). Inadequate fertilization will cause poor 1 ocular jelly development and the Ill resulting fruit will be misshapen. This may explain not only why the total weight of culled fruit did not drop proportionally to the total yield (Tables 20 and 21) but also why yield reductions 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 entire plant will be affected, the number of marketed fruit would remain the same. Since the leafminers usually attack the lower and middle leaves first (Wilcox and Howland, 1952) their effect on net photosynthesis will be minimal. The younger leaves which are the most important to the plant and the removal of which would harm the plant more than the removal of the lower ones (Harper, 1977), are normally only slightly damaged. Only in case of yery serious outbreaks of the vegetable leafminer 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%) does as much harm to the tomato plant as a high level defoliation does over a short period of time when considering the first harvest. Vigor and transpiration are affected more often and the plant will have to divert 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 removed to significantly reduce yield of staked 'Walter' tomatoes (Jones, 1980) is probably due to the fact that in Jones' experiments no damage was inflicted to the plants in the especially sensitive pre- bloom period. The minimal reduction of total yield in the repeated 112 defoliation experiments 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 leaf mines 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 most 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 affect his total income from the tomato harvest most. When comparing the influence of defoliation on yield of all extra large and large fruit with that on gross revenue (Tables 11 and 18; and Tables 26 and 30), the importance of these fruit sizes to growers is obvious. Although the weight of the medium size fruit may also be reduced, the effect of this reduction is a relatively small component of the total yield. As a result, a significant reduction in total yield corresponds to a significant reduction in gross revenue so that, from a practical point of view, total yield data give a very good indication of the gross revenue a grower may expect from his tomato crop. In the present study all marketable fruit, irrespective of its position within the canopy was harvested for further analysis. 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 113 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 for further processing may well be equal or even greater than that originating from healthy plants. In fact the use of defoliants to increase the number of fruit picked has been suggested (Vittum, 1957). Considering the differential sensitivity to defoliation in the course of the development of the tomato plants, the economic threshold of the leafminer varies during the season. Monitoring of the infestation levels is especially advisable early in the season and at mid-season. Conclusion Depending on the time and the frequency 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 because of an increase in photosynthetic activity of the remaining foliage. Repeated defoliation at intermediate levels can be detrimental to yield and quality of the tomatoes because of more continuous interference with the plants' metabolism and diversion of the energy supply from the fruit to the vegetative parts of the plants in order to optimize its photosynthetical ly active leaf area. Before and 114 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 defoliation also occurs when interference with nutrient translocation from the leaves to the fruit is ^ery important. Near harvest the fruit is especially sensitive to radiation exposure which may result in sunscald or decay or both. At this time the reduction of the fruit weight will in practice be offset by the larger number of fruit harvested by pickers because of the greater ease with which the fruit can be located and, therefore, the greater speed with which the pickers can fulfill their set quota. The following recommendations can be made to the grower. 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 undertaken until defoliation exceeds the 50% level. If, after specific insecticidal treatments for leafminer control have been applied, a further defoliation of 10% or more occurs, additional treatments are indicated. 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. CHAPTER IV MICRO-ORGANISMS ASSOCIATED WITH MINES OF Liriomyza sativae BLANCHARD Introduction In several crops leaf mines have frequently been observed to be the center of an area characterized by yellowing, necrosis, or both. Leaf mining insects occur in a very large number of plant species (Needham et al . , 1928; Hering, 1951; Spencer, 1973a) and have been reported to cause various kinds of damage to the leaves. Relatively few reports have been made suggesting that these symptoms were associat- ed with organisms other than the leaf mining insects themselves. The mines have been recognized as niches with an ideal environment for the development of fungi and other micro-organisms, mainly as parasites of the larvae (Hering, 1951). Discoloration of the mines and the leaf tissues in their vicinity has been explained by decay of portions of the tissue, by substances produced by either host plant or leafminer larvae, or by the undernourishment of some cells adjacent to the mine (Hering, 1951). Wounds created by the piercing of the leaf epidermis by leafminer adults have been suggested as ports of entry for saprophytic micro- organisms (Portier, 1930; Hering, 1951) and plant pathogens (Eichman, 1943; Spencer, 1973a; Andaloro and Peters, 1977; Kamm, 1977). A relation between leaf damage by mining insects and subsequent disease 115 116 development has been shown for needle blight and Cecidomyid gall midges which mine red pine needles (Haddow and Adamson, 1939; Haddow, 1941), citrus canker and the citrus leafminer, Phyllocnistis citrella Stainton, which mines leaves of rough lemon (Sohi and Sandhu, 1968), and celery heart rot and the miners Scaptomyza g rami n urn and Elachiptera costata which mine the petioles of celery plants (Leach, 1927). A very large number of micro-organisms may be present in the phylloplane of plants (Dickinson, 1976) the majority of which reaches the leaf by wind or rain (Gregory, 1971). Leafminer adults have been shown capable of transmitting pathogenic viruses (Costa et al . , 1958; Zitter and Tsai , 1977) and bacteria (Leach, 1927; Singh et al . , 1977). The objectives of this study were to (1) identify the organism or organisms responsible for the yellowing and necrosis associated with leaf mines in tomato, (2) identify any micro-organisms, especially fungi, associated with both healthy leaves and leaves mined but not showing any disease symptoms, and (3) find possible associations of the pathogen(s) with the leaf- miner adults. Materials and Methods Isolation from Leaves Leaves were collected in a number of commercial tomato fields in the Homestead area of Dade County, Florida. Tomato plants of the 117 cultivar Walter growing either on open ground or on plastic mulch were sampled. Care was taken that the leaflets collected for isolations did not show any signs of senescence so that the yellowing associated with the mines was not the result of natural deterioration of the leaf tissues. Leaflets which were mined but did not show any yellowing as well as healthy leaves were collected from comparable areas within the plant canopy. Surface sterilization was carried out in two ways. One was by cutting discs with a diameter of approximately 3 mm out of the leaf with a cork borer, immersing these in a 1% sodium hypochlorite solution, containing 1 drop of Tween-20 per 100 ml, for 1 to 2 minutes followed by three rinses in sterile distilled water. The other method used consisted of gently rubbing both leaf surfaces with a cotton swab soaked in 70% ethyl alcohol for 2 to 3 seconds, followed by cutting leaf discs as described above. The latter method proved more consistent and resulted in fewer contaminated cultures than the first, and, therefore, was employed more frequently. The discs were cut from diseased leaves in such a way that they contained both yellowed and healthy tissue, or yellowed and necrotic tissue plus a very small portion of the mine. Discs from non-yellow mines were cut to contain apparently healthy leaf tissue plus a very small portion of the mine. Healthy leaves were cut in areas comparable to those where leaf mines occurred in the infested leaflets. The discs were transferred onto potato dextrose agar (PDA) containing 100 ppm streptomycin sulphate and 150 ppm benomyl in petri dishes (PSBA plates). Benomyl was added because it has been shown ineffective in controlling the disease associated with the leaf mines. 118 The dishes were examined for fungal growth originating at the discs after 3 to 4 days of incubation in the dark at 25°C. Individual colonies were then transferred to PDA plates, a process which was repeated, when necessary, to obtain pure cultures. Any bacterial colonies arising from leaf discs were also transferred to PDA dishes. All cultures were incubated for 1 to 2 weeks in the dark at 25°C. When the fungal mycelium covered approximately 60% of the agar's surface, the cultures were exposed for alternating periods of 12 hours to U.V. radiation and to darkness for three days in order to induce sporulation. Pathogenicity Tests Tomato plants of the cultivar Walter were grown at a temperature of 21 + 1 C in a growth chamber in pots containing a peat:vermiculite (1:1, v/v) mixture. Fungal tests. Of the fungal cultures obtained by isolation from yellowed mines, 8 were chosen for pathogenicity tests; of those from non-yellowed mines, 4 were tested. These isolates were inoculated on the third or fourth oldest leaf of 30-50 cm tall plants. Some of the tomato leaflets were wounded with a mounted needle before inoculation. Inoculum was obtained by scraping the surface of 1 month-old cultures with a sterile ni chrome wire loop and then flooding the dishes with 10 ml sterile distilled water. The largest mycelial fragments were removed by filtering the suspension through two layers of cheesecloth. Half of the filtrate was diluted by adding an equal volume of distilled water, while to the other half an equal amount of a 1% (w/v) sucrose solution was 119 added. Thirty two tomato plants were divided into 8 treatment groups with 4 plants in each group. The leaflets were sprayed with a hand atomizer (Table 34). The leaflets were then allowed to dry and enclosed in a plastic bag for 24 hours to maintain high humidity. The plants were examined 4 to 6 days after inoculation for the development of disease symptoms. Bacterial tests. Inoculation was carried out on plants similar to those used in the fungal tests. Again 8 cultures originating from diseased mines were tested. Bacterial suspensions were obtained by flooding petri-dish cultures with distilled water. The suspensions were then cotton- swabbed on the upper surface of both the wounded and unwounded leaflets of four different plants for each treatment. The inoculated leaflets were subsequently wetted with distilled water by a hand atomizer and then enclosed in plastic bags for 24 hours. The plants were examined for necrotic lesions with yellow halos 6 to 8 days after inoculation. Isolation from Flies Adult female leafminers ovipositing on tomato leaves in the field were aspired into sterile plastic vials. Of these flies some were released into a petri dish containing PSBA in the laboratory, one fly per dish, and allowed to move around for 15 minutes. Other flies were surface sterilized in groups of 5 as described by Noble et al . (1978) and crushed in 3 ml sterile water. Of the resulting suspension 1 ml was then plated on PSBA in petri dishes which subsequently were incubated in the dark at 25°C. Pure culture of any fungi developing on the piates 120 to i — 01 o CO >, ■<- -r- Ul -I— •!— i — CO t- 121 were obtained and their speculation achieved as with the leaf disc isolates described above. Results Symptoms The symptoms developing around the infected portion of the mine varied considerably. In some cases the diseased area was rather small, approximately 2 to 3 mm in diameter, and consisted of necrotic tissue surrounded by a narrow, often faint, yellow halo. Occasionaly yellowing of up to 75% of the entire leaflet area was symptomatic. No necrosis was then evident except in the leaf mine itself. Most infected mines showed symptoms somewhere between these two extremes. On a few occasions two separate zones of necrosis and yellowing were associated with the same mine. Very rarely was the entire mine surrounded by a chlorotic or necrotic zone. If the leaflet was severely mined and more than one mine was infected, a shriveling of the infected area or death of the entire leaflet often resulted. The percentage of mines with yellow tissue varied from 5.0% to 88.9/0 per plant in 1978 in one field of the Homestead Agricultural Research and Education Center. Isolations from Leaves and Flies ^Jery few fungi were isolated from surface sterilized, apparently healthy leaflets (Table 35). Surface sterilization with ethyl alcohol resulted in fewer isolates obtained than with sodium hypochlorite. 122 r— 03 03 "O OJ -i- o Q. 3 CO- O os u „ a; ■a T3 a; 03 N O i — 4- •!— O 1 ITS (1) o -a rO 03 4- Q) S_ +-> 3 (/) in a> f= e o o X +-> Lf) un *3" ^t 03 to +J u O co i- -1- oj en 13 U 03 in i — T3 03 N S a. O 4- -r- 10 r~ S_ p— i- o +J 3 •!- C 4-> O) in S- 03 03 s: ai CD E +-> i- O 10 o +-> 1 CD o c c S- 2 ■i- QJ o o r— +-> r- S- a. 03 S: CD E "a W N in Ifi N N oo oo oo oo un ld r»* i-H co co oo cT> cm oo c\j oo <>r «j- r- 1 O ■— I .— I C\J O CSJ O n h io n ==CCQ=ICQCCCQ> o c u_ o C " e£ O != S- 3 M- O o) a> (0 T3 r— Q O to M- •i- O >i a. jC Q. a. m ! < 125 fc 03 O T3 S_ -r- 4- S- O T3 r— 0) U. O O) r— "O <+- rO o a S_ -i- >> 9- co ^H ■a 126 X3 S- -r- -r- 1/1 e£ CO ro 3 03 S_ i- r— 0) ro ^ C .c1 I/) i. Q-i -C O) E o 4-> "O aio ai s +-> O 00 r— a; +-> sr o 03 = i — 3 Q. e r— -o ■r- 00 (J i 03 = E 00 137 At low mine densities the effect on net photosynthesis will be minimal since most leaf mines occur near the leaf margins and do not sever any veins and, therefore, interfere only slightly, if at all, with nutrient transport within the leaf. From measurements of the leaf area affected by the different instars of the vegetable leafminer, Liriomyza sativae Blanchard, and a number of other Agromyzid leafminers (Table 40) it is obvious that in case death of the larvae occurs in the first or second instar, the damage to the leaf tissues, which amounts to less than 0.5% of the area of a tomato leaflet for the vegetable leafminer, remains so small that the impact on overall photosynthesis activity of the leaflet becomes negligible. However, as a result of serious leafminer outbreaks, the density of the mines may increase to such an extent that translocation of nutrients and thereby the metabolism of the mesophyll cells distal to the mines will be affected (Hering, 1951). In this case the photo- synthesis rate of the tomato leaf will be reduced disproportionally to the actual injury. The impairment of the metabolism can become so severe that death of the entire affected leaf area results. Conclusions The effect of a single mine of the vegetable leafminer in a tomato leaflet reduces the net photosynthesis of the leaflet proportionally to the area that the mine occupies. A higher mine density in tomato leaflets will reduce the net photosynthesis rate more than the additive effect of individual mines due to interference with translocation of nutrients in the leaf's mesophyll. 138 >> C i-t -a T3 1 o o > ^ H r-l _CT 139 Control of the leafminer by means of efficient insecticides or Hymenopterous parasites which will kill the larvae in their first or second instar will result in a negligible effect on the photosynthesis potential of the tomato leaves. CHAPTER VI CONCLUSIONS Although leafminers can do serious damage to the leaf tissues of tomato plants, the density of the leaf mines is rarely high enough to cause serious defoliation by itself. Only in the seedling stage when the total leaf area of the tomato plants is small will consumption of the entire photosynthetically active tissue occur easily. The most important factor in the occurrence of leaf deterioration and subsequent abscission is the weak pathogen, Alternaria altemata, which is capable of destroying an entire leaflet. This can happen even if only a single mine is present in a leaflet and becomes colonized by the fungus. Low leafminer densities are, therefore, not necessarily a measure of potential damage to the tomato plants. Additional damage associated with leaf mines can be caused by Xanthomonas vesicatoria which may enter the mines. 0 The lower leaves of the tomato plants which act more as metablic sinks than as photosynthetically active organs are dispensable as can be concluded from the absence of effects of defoliation of lower plant canopies on fruit development. The upper leaves are more important to the plant than the middle and lower ones and, because of their younger age, are more resistant to infection. Since leafminers usually attack only the lower and middle leaves, infestations except at wery high levels usually have relatively little effect on the yield and, therefore, on MO 141 the gross revenue of the tomato crop. The tomato plants exhibit a differential sensitivity to defoliation during the growing season. The most sensitive times are early in the season and at mid-season. Still, at least 60% of the foliage has to be removed before significant reduction in the yield of the fruit in the two largest size categories as well as the total yield of marketable fruit can be observed. Repeated defoliation is tolerated by the tomato plants at lower levels with removal of 40% of the foliage resulting in significant yield reduction. The weight of all marketable fruit at any level of defoliation is significantly correlated with the gross revenue that the grower would obtain from that yield, based on different prices for the different size categories. If large leafminer populations occur, then parasites, if they are present, can ensure that the leafminer larvae will be killed before the damage to the tomato leaflet becomes severe enough for the pathogen to establish itself sufficiently to affect the tissue around the mine. An effective way to avoid concern about possible damage to tomato plants by the leafminer-Alternaria complex is, therefore, to ensure the presence of sufficient parasites in the field which can effectively control the leafminer population as was the case before the first serious outbreaks which resulted from the intensive use of pesticides. The application of sound pest management practices appears to offer the best chance of achieving maximum net revenue in crops where the leafminer can be a serious problem. 142 If, however, the parasite population is ineffective in controlling the vegetable leafminer, insecticide applications specifically to control the leafminer are required. 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Cost of producing winter fresh vegetables in Florida and West Mexico. Vegetable situation. U.S. Dep. Agric. Econ. Stat. Coop. Serv. TVS-212:25-28. Zitter, T.A. and J.H. Tsai. 1977. Transmission of three potyviruses by the leafminer, Liriomyza sativae (Diptera: Agromyzidae) . Plant Dis. Rep. 61:1025-1029. BIOGRAPHICAL SKETCH Jozef Leo Will em Keularts was born on August 10, 1945, in Heerlen, The Netherlands. After completing secondary school at the St. Bernardinus College in Heerlen in 1963, he received a scholarship to the Catholic University of Nijmegen, The Netherlands. In 1969 Jozef graduated from the Catholic University of Nijmegen with the title of Doctorandus in Biology. In the same year, Jozef fulfilled the compulsory Armed Services requirements of the Dutch Army, serving as a radio communications operator in the Cavalry Division. Following his military service in 1971, Jozef taught biology and agricultural science to senior forms in preparation for their Cambridge examinations at Mumbwa Secondary School, The Republic of Zambia, Africa. He left Zambia in 1976, returning to the Catholic University of Nijmegen to study the ultrastructure of mites, From 1977 to 1980, Jozef has been a graduate student in the Department of Entomology and Nematology at the University of Florida. Upon completing the requirements for the degree of Doctor of Philosophy, he plans to take up a position as Lecturer of Entomology at the University of Malawi, The Republic of Malawi, Africa. 154 I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. L3. Van H. Waddill, Chairman Associate Professor of Entomology and Nematology I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. ■> 0 -'f- TW, John R. Strayer j Profes'sor of Entomology and Nematology I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Robert T. McMillan, Jr. Associate Professor of Plant Pathology I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Kenneth L. Pohronezny D Q Assistant Professor of Plant Pathology This dissertation was submitted to the Graduate Faculty of the College of Agriculture and to the Graduate Council, and was accepted as partial fulfillment of the requirements for the degree of Doctor of Philosophy. August 1980 Dean, College of Agriculture Dean, Graduate School fill!