UTTERWORTH 0261-2194(95)00032-l

Crop I'rornrr,,~~ \ 01 IJ. No. 8, pp 6X34,x7. ,YY5 EINEMANN Fkev1er Science l.ld

Printed m Great Bnram O?hl-2lYJiY5 $10 (ICI + I) 00

Treatment decisions based on egg scouting for tomato fruitworm, Helicoverpa zea (Boddie), reduce insecticide use in tomato G. W. Zehnder,*+ E. J. Sikora* and W. R. Goodman *Deparfment of Entomology, Department of Plant Pathology, and Depatiment of Agricuiturat

Economics and Rural Sociology, Auburn University, Auburn, AL 36849, USA

Field experiments were conducted to evaluate the effectiveness of a tomato fruitworm, Helicoverpa zea (Boddie), management program where insecticide application was made only when fruitworm eggs were detected on tomato foliage. Fruit damage and number of insecticide applications were compared between the egg scouting program and a standard fruitworm management program where insecticides wcrc applied on a weekly schedule. On average, 59 and 43% fewer insecticide applications (for csfenvalerate and Bacillus thuringiensis, respectively) were required in the egg scouting program, compared with the weekly spray program, without any reduction in marketable yield. The average seasonal insecticide cost savings associated with the use of the egg scouting program were $US109.33 and $US93.33 per ha for esfenvaleratc and B. thuringiensis, respectively. When scouting was used, average net returns, considering machinery and labor costs, were $USl46.45 and $US164.33 per ha higher for esfenvalcrate and R. thuringiensis, respectively.

Keywords: Helicoverpa zea; tomato fruitworm; tomato; scouting; insecticide treatment; cost

The tomato fruitworm, Helicoverpa zea (Boddie) is the most serious insect pest of fresh-market tomatoes grown in Alabama. Fruitworm larvae feed directly on developing fruit, thereby reducing marketable yields. To prevent fruitworm damage, Alabama tomato growers spray insecticides at 4-7 day intervals beginning at flowering and continuing through harvest. This preventive approach to fruitworm control is generally effective, but has several drawbacks, including reduced profits from high insecticide costs, destruction of natural enemy populations (Campbell, Walgenbach and Kennedy, 1991), and build-up of insecticide residues on tomato fruit (Spittler, Argauer, Lisk, Mumma, Winnett and Ferro, 1984) and in the environ- ment. Therefore, a practical, decision-based fruitworm management program is needed as an alternative to preventative, calendar-based sprays. Integrated pest management (IPM) programs have been developed for processing tomatoes in California and Mexico (Goode11 and Zalom, 1993; Bolkan and Reinert, 1994) and in Florida for fresh-market tomatoes (Pohronezny, Waddill, Schuster and Sonada, 1986). In these programs, scouting of tomato foliage is done to estimate the population density of various insect pests and to determine when insecticide sprays are needed. Because tomato fruitworm larvae enter fruit shortly after hatching, insecticides applied to coincide with egg hatch are most effective (Hoffman, Wilson, Zalom and Hilton, 1990). Therefore, treatment thresholds for fruitworm are based on the presence of eggs, with the actual threshold varying by location. In California

Author to whom correspondcncc should be addressed

processing tomatoes, a treatment threshold of four eggs per 30 tomato leaves is used, although thresholds may be adjusted based on the percentage of parasitized (black) eggs found (Hoffman et al., 1990). The Mexican processing tomato industry uses a threshold of 16 viable fruitworm eggs per 100 randomly picked leaves (Bolkan and Reinert, 1994). Fruitworm egg scouting is done in Florida fresh-market tomatoes, but the tolerance for fruitworm damage is extremely low and a treatment is recommended if any fruitworm eggs are detected in the field (Pohronezny et af., 1986). Although various tomato fruitworm treatment thresholds are being used in fresh-market tomatoes, to our knowledge replicated trials have not been conducted to quantify fruitworm damage when insecticides are applied only when fruitworm eggs are detected by scouting, and to compare the scouting program with a calendar-based spray program. This study addresses the above, in addition to estimating the insecticide costs and produc- tion profits associated with both programs.

Materials and methods

Experimental plan and cultural practices

Tomato plantings were established in 1992 and 1993 at the North Alabama Horticulture Substation in Cullman, Alabama. In 1992, Colonial tomatoes were trans- planted on 18 May as a spring crop, and Olympic tomatoes were transplanted on 22 July as a summer crop. Colonial transplants were used in both spring and summer trials in 1993; transplant dates were 10 May and 14 June for the spring and summer trials,

Crop Protection 1995 Volume 14 Number 8 683

Reduction of insecticide use in tomato: G.W. Zehnder et al.

respectively. In both years, tomatoes were grown on raised beds with plastic mulch (black in spring and white in summer) and drip irrigation using standard cultural practices for staked tomato production in Alabama (Kovach, Dangler, Sikora, Zehnder, Patterson and Williams, 1992). Treatment plots consisted of one 9.1 m treatment row borderd on both sides by untreated buffer rows. Plants were spaced 60 cm apart with 2.23 cm between rows.

Experimental design was a randomized complete block with four replications. Treatments, described in Table I, consisted of foliar sprays of esfenvalerate (Asana XL, E.I. du Pont de Nemours and Company, Wilmington, DE) and Bacillus thuringiensis ssp. kurstaki (Javelin WG, Sandoz Crop Protection, Des Plaines, IL), alone or in combination, applied either on schedule (to simulate conventional treatment) or based on scouting for fruitworm eggs. Dimethoate (Cygon 400, American Cyanamid Company, Wayne, NJ) was applied as needed to all plots, including the control, at the rate of 0.56 kg/ha for thrips control until the flowering stage when dimethoate sprays were dis- continued.

Insect scouting, application of treatments, tomato harvest and data analysis

Untreated control plots and plots receiving treatments based on scouting were sampled twice weekly by examining the first fully expanded leaf below the highest open flower on 10 plants per plot (Zalom, Wilson and Smith, 1983; University of California, 1990; Campbell et al., 1991). Sprays in scouting treatments were applied when one or more white fruitworm eggs were detected on any of the plants sampled. Tomato fruitworm eggs turn black when parasitized, and black eggs were not considered in the treatment decision process. However, the eggs do not turn black until about 4 days after parasitization (Graham, 1970), and some of the white eggs detected on the foliage may actually have been parasitized. The treatment thres- hold of al.0 fruitworm egg per treatment was used because of the low tolerance for insect damage in the fresh-market tomato industry, and for ease of use (sampling can be discontinued if one egg is found).

Insecticide sprays were applied with a tractor- mounted sprayer equipped with vertical drop spray booms containing two to six nozzles per row (one to three nozzles per side); nozzles were added as plants grew. Spray volume (280-935 l/ha) increased as nozzle number increased but spray pressure remained constant

at 4.2 kg/cm2. Sprays were usually applied within 24 h of detection of fruitworm eggs, but some sprays were unavoidably delayed up to 3 days after egg detection because of inclement weather. However, neonate tomato fruitworm larvae feed on foliage before entering fruit (Campbell et al., 1991). Therefore, it is likely that neonates were exposed to insecticides even if applied 3 days after hatching.

Harvesting was done at 4-7 day intervals by picking fruit at the breaker stage of maturity or later from each treatment and recording the total numbers of fruit and the numbers with fruitworm feeding damage. Fruit with entry holes were considered damaged by fruitworm whereas a low percentage of fruit with surface feeding damage characteristic of Spodoptera exigua (Hiibner) and Trichopfusia ni (Hiibner) were not considered in the analyses. The weight of undamaged (marketable) fruit produced in each plot was also determined.

Percentage damaged fruit values(p) were transformed to arcsine Vp/lOO before analysis. Fruit weights and transformed damaged fruit values were subjected to analysis of variance (SAS Institute, 1990), and treat- ment means were compared using the Ryan-Einot- Gabriel-Welsch multiple F test.

A fresh-market tomato production budget (Good- man, 1992) was used to estimate production costs and returns associated with use of the various fruitworm control programs. The budget was entered into a computer spreadsheet program to facilitate the calcula- tion of cost and return values.

Results

In 1992, the percentage of fruitworm-damaged tomato fruit was lower in the spring than in the summer trial (Table 2). In the spring, a seasonal average of only 8.0% damaged fruit was recorded in the untreated control with a range of 0.5-2.3% damage among the insecticide treatments. Fruitworm egg counts were correspondingly low, not exceeding 1 .O egg per treat- ment sample date from 17 July through the harvest period (Table 3). Because of low egg counts in the 1992 spring trial, only two to three sprays were applied in the scouting treatments (2, 3 and 6), whereas seven to 10 sprays were made in the scheduled treatments (1,4 and 5) (Table 4).

Fruit damage was more severe in the 1992 summer trial, with 74.1% peak fruit damage on 19 October (first harvest date) in the untreated control plots and average damage over the season above 50% (Table 2).

Table 1. Insecticide treatment programs for control of fruitworm damage in tomato, 1992 and 1993*

Treatment Rate (Al)/ha Spray application timing

I. 2. 3 4:

5. 6. 7.

Esfenvalerate

Esfenvalerate Esfenvalerate + 3.t k B.t k B.t k 13.t. k Untreated control

56.0 g 56.0 g

0.80 kg 1.12 kg

1.12 kg I .26 kg

Weekly beginning at flowering Only when fruitworm eggs detected

Every 4 days beginning when fruitworm eggs detected

Every 7 days beginning when fruitworm eggs detected Only when fruitworm eggs detected

iTreatment 3 not included in 1993 experiments Bacillus thunngiensis ssp. kursfaki rate values are amounts of formulated material (Javelin WGrM)

684 Crop Protection 1995 Volume 14 Number 8

Reduction of insecticide use in tomato: G.W. Zehnder et a/.

Table 2. Mean percentage (I SEM) of tomato fruit with fruitworm damage, 1992 and 1993*

Treatment 1902

Spring (4)* Summer (3). I YY3

Spring (5)

I. Esfen. weekly 0.1 f O.Ic 13.3 i- 7.6b 3.6 k 0.7b X.3 !I 2.Obc 2. Esfen. based on scouting 0.6 * 0.3bc 6.3 + 2.Sb I.0 + 0.6b 3.7 +- l.Sc 3. E&n. + M. t k hased on scouting I .O -c 0.4bc 2.7 k 1.2b NA NA 4. t?.t k cvcry 4 days 0.5 * 0.2bc 5.3 f 2.7b 2.0 t 0.7b 7.Y f 1.7bc 5. R.t k every 7 day\ 2.3 ? 0.7b 10.7 + -t.Yb 3.6 -c I.lb x.0 f 2.Yc 6. h.t k based on scouting 1.4 f 0.4bc 13.Y i 3.Yb 5.8 f I.4b 6.2 i 1.4, 7. Untreated control X.0 f l.Ja 52.7 -t 6.la 25.9 + 3.oa 26.1 i 3.4a

Summer (4)

Mean\ wnhln coium~~~ \hnring a letter iI1 common arc not signifxantly different (P > 0.05: Ryan-Einot-C;abrieI-Welsch multiple F test). NA, not applicable Data comhmcd for all harvest dates (number of harvests in parentheses). Sprmg. IYY2 harvest dates: IO. 17.24 and 31 August. Summer, lYY2 harvest dates: IS and 26

Octohcr and I November. Spring. IYYi harvat dates: 28 July. and 3. Y. 12 and 16 August. Summer, 1493 harvest data: 27 and 31 August and 7 and I3 September. ~l\lcnvaleratc H~c~i//,c\ rhrt,_r~r,qrrrrr/\ \pp. h~,v\r 0.05) different from other insecticide treatments, the least fruit damage occurred in the

Crop Protection 1995 Volume 14 Number 8 685

Reduction of insecticide use in tomato: G.W. Zehnder et al.

esfenvalerate + B. thuringiensis treatment that was based on scouting (treatment 3) (Table 2). This treatment received only four sprays, compared with eight to 13 sprays made in the treatments applied on schedule (Table 4). Campbell et al. (1991) also found the combination of esfenvalerate + B. thuringiensis to be superior to other registered tomato insecticides for protection against fruitworm damage.

The percentge of tomato fruit with fruitworm feeding damage averaged approximately 26% in each of the 1993 trials (Table 2), with peak damage (46.9 and 47.1% damaged fruit) occurring on the first harvest dates. Fruitworm egg counts were low in 1993 but eggs were detected throughout the spring and summer egg sampling periods until just before first harvest (Table 3). As in 1992, fruit damage was significantly (P < 0.05) reduced in all 1993 insecticide treatments (both trials) compared with the untreated control (Table 2). In both 1993 trials, fruit damage was generally lower in the esfenvalerate scouting treatment (treatment 2) than in the weekly esfenvalerate treatment (treatment l), yet the frequency of insecticide application was reduced by at least half in the esfenvalerate scouting treatment (Table 4). Average fruit damage in the B. thuringiensis treatments (3,4 and 5) ranged from 2.0 to 8.0% with no significant differences among fruit damage means (Table 2). The B. thuringiensis treatment based on scouting (treatment 6) required the fewest sprays (four

and five sprays in the spring and summer plantings, respectively) of all the B. thuringiensis treatments (Table 4).

There were no significant (P > 0.05) differences in average total marketable tomato fruit weight values among insecticide treatments in both years of the study, and fruit weights in the insecticide-treated plots were not significantly different from the untreated control (Table 5). Lack of significance is due, in part, to high variability in fruit weight values among plots, and also to the relatively low number of observations used to calculate the means (four replicates times the number of harvest dates). In addition, the low percentage of fruit damage in insecticide-treated plots contributed to similar yields among these treatments. However, marketable fruit weight in the best insecticide treat- ments ranged from 18.8 to 59.4% higher than in the untreated control over the four experiment trials (Table 5).

On average, the per-season insecticide cost savings associated with use of the scouting programs were $US109.23 and $US93.33 per ha for esfenvalerate and B. thuringiensis, respectively, compared with the weekly spray programs (Table 6). Average net returns, con- sidering machinery and labor (including scouting) costs, were $US146.45 and $US164.33 per ha higher for esfenvalerate and B. thuringiensis, respectively, when scouting was used. Returns were greater than average

Table 5. Mean weight per harvest of marketable tomato fruit (in thousands of kg/ha + SEM) in scouting and calendar-based tomato fruitworm control programs*

Treatment

1992 Summer trial (3)

Spring trial (5)

1993 Summer trial (4)

I. Esfen. j weekly 20.5 f 1.9 19.4 I 7.2 16.0 * 7.6 12.8 f 8.1 2. Esfen.> based on scouting 22.7 * 2.2 18.8 t 7.0 15.) + 4.5 14.8 * 4.3

4: 3 Esfen(.l Bs k, \ + R.t 4 k, diys based on scouting every 21.5 22.7 + + 2.3 1.7 25.3 18.6 + t 9.) 6.8 15.3 NAII ? 10.0 14.4 NAII 2 4.1 5. B.t k* 7 days every 20.4 f 2.3 21.9 i 8.2 14.4 2 7.8 13.2 i 8.6 6. B.f ks based on scouting 21.9 f 1.6 17.8 + 6.7 14.1 + 4.1 13.7 rfr 3.9 7. Untreated control 18.5 * 1.7 12.7 + 4.6 6.5 * I.9 9.2 f 2.6

Means within columns are not significantly different (P > 0.05; Ryan-Einot-Gabriel-Welsch multiple F test)

Values extrapolated to amounts/ha based on weight of harvested fruit in each plot Numbcrs in parentheses are the number of harvest dates per season; means calculated based on four replicates per treatment times the number of harvest dates

Esfenvalerate

8.1 k is 8ocillrr.v /hrrringio~A spp. klrrsroki (Javelin WG) II Not applicable: treatment 3 not included in lYY3 experiments

Table 6. Comparison of insecticide costs and net production returns for scouting and calendar-based tomato fruitworm control programs

Treatment

Esfcn.$ weekly Esfen. based on scouting B.1 kll 4 days every R.t k) 7 days every R.f kll based on scouting

Spring, IYY2I Insecticide cost Net return

($/ha) ($/ha)

20h.Yh 3,001.44 45.99 3.177.30

321.10 2&X36 224.17 2.970.40 96.33 3.113.66

Average over four seasons Insecticide cost Net return

($/ha) ($/ha)l

183.Y7 3,008.56 74.74 3,154.91

361.24 2.784.41 224.17 2.021.37 128.44 3.085.70

Season with lowest fruitworm population density

Per season cost of insecticide used in the spray program treatment

,.Per season net return (profit) above all tomato production expenses, including machinery and labor costs. Calculated based on a budget developed for Alabama

fresh-market tomato productmn 33fealerate

IBacillu~ thuringicnsia \pp, ku~uukj (Javelin WC;)

666 Crop Protection 1995 Volume 14 Number 8

deduction of insecticide use in tomato: G.W. Zehnder et a/.

in the spring 1992 trial because the egg scouting program determined that fruitworm populations were low (based on finding few eggs) and, therefore, insecticide sprays were rarely recommended.

Discussion

The low number of esfenvalerate applications in the scouting treatment (Table 4) may have contributed to higher natural enemy populations than in the weekly esfenvalerate treatment, and this may be one explana- tion for the lower fruitworm damage values in the scouting treatment (Table 2). Although natural enemy populations were not quantified in this study, previous studies have demonstrated that reducing the frequency of insecticide applications enhances the survival of beneficial arthropods in tomato cropping systems. Pyrethroid insecticides, like esfenvalerate used in our study, have long residual activity on foliage (Walgen- bath, Leidy and Sheets, 1991) and have been shown to inhibit parasitization of fruitworm eggs by Tricho- grammu (Hymenoptera: Trichogrammatidae) species up to 21 days after application (Jacobs, Kouskolekas and Gross. 1984). A North Carolina study also demon- strated that the incidence of fruitworm egg parasitiza- tion by Trichogramma was lower in tomatoes treated with esfenvalerate than when other insecticides were applied (Campbell et al., 1991).

Our results demonstrate that implementation of a fruitworm scouting program can result in increased returns for tomato growers, compared with calendar- based spray programs. with no reduction in marketable yield. On average, 59 and 43% fewer insecticide applications (for esfenvalerate and B. thuringiensis, respectively) were required in the egg scouting program, compared with the weekly spray program (Table 4). The cost/return analysis (Table 6) also shows that the cost of scouting (approximately $US14.00 per ha) is more than returned by the savings in insecticide costs. In a calendar-based program where growers may have no knowledge of pest density, insecticide sprays are applied on schedule as a precaution to prevent insect damage. even if the actual pest population density is low or nonexistent. Scouting provides the farmer with knowledge of pest density that is essential for a transition from calendar-based spray programs to a more sustainable approach where insecticides are applied only when necessary.

Acknowledgements

This project was supported by the Alabama Co- operative Extension Service. This paper is Alabama

Agricultural Experiment Station Journal Series #17- 944916.

References

Bolkan, H. A. and Reinert, W. A. (1994) Developing and implemcnt- ing IPM strategies to assist farmers: an industry approach. P/ant LG. 78, s45-5.50

Campbell, C. D., Walgenbach, J. F. and Kennedy, G. G. ( IYY 1) Effect of parasitoids on lepidopterous pests in insecticide-treated and

untrcatcd tomatoes in western North Carolina. 1. Ewn. Entomol. 84, 1662-I667

Goodell, P. B. and Zalom, F. G. (1993) The potential for integrated pest management in California vegetable production. In: S~rccessfitl

Impkmentation of Integrated Pest Manugement for Agriculturul Crops (Ed. by A. R. Leslie and G. W. Cuperus) pp. 75-04. CRC Press. Boca Raton. Florida

Goodman, W. R. (IYYZ) Entcrprisc budgets for vcgetablc crop production. Alabama Cooperative Extension Service. AECBlJD l-4.

January. I092

Graham, H. M. (lY70) Parasitism of eggs of bollworms, tobacco budworms and loopers by Trichogramma .sem@matum (Hymcn- optera: Chalcididae) in the lower Rio Grande Valley, Texas. J. Econ. Entomol. 63, 6X6-688

Hoffman, M. P., Wilson, L. T., Zalom, F. G. and Hildon, R. J. ( 1900) Parasitism of He/&this zea (Lcpidoptcra: Noctuidac) eggs: effect on pest managcmcnt decision rules for processing tomatoes in the Sacramento Valley of California. 62~. Entomol. 19, 753-763

Jacobs, R. J., Kouskolekas, C. A. and Gross, H. R. (lY84) Response of Tric~hogrammu pretiosum (Hymenoptera: Trichogrammatidae) to rcsiducs of pcrmethrin and cndosulfan. Env. Entomol. 18. 355-358

Kovach, S., Dangler, J., Sikora, E. J., Zehnder, G. W., Patterson, M. and Williams, J. 1,. (lYY2) Commrrcial Tomato Production. Alabama Cooperative Extension Service

Pohronezny, K., Waddill, V. H., Schuster, D. J. and Sonoda, R. M. (lY86) Integrated pest management for Florida tomatoes. fkmt Dir. 70, Yf%lO2

SAS Institute ( IYYO) SASISTAT Uxrs Guide. Vcxsion h, Fourth edition. SAS Institute, Gary. North Carolina

Spittler, T. D., Argauer, R. J., Lisk, D. J., Mumma, R. O., Winnett, G. and Ferro, D. N. (1984) Gas chromatographic determination of

fcnvalcratc insecticide rcsiducs in processed tomato products and by-

products. J. Aswc. Ojf. Anal. Chum. 67. 824-826

University of California (IYYO) Insects and related pests. In: fntqyzted Pest Manugement for Tomatocj. third edition (Ed. by M. L. Flint) pp. 33-59. University of California Division of Agriculture and

Natural Resources, Publication 3274

Walgenbach, J. F., Leidy, R. B. and Sheets, T. J. (IYY I) Pcrsistcncc of insecticides on tomato foliage and implications for control of tomato

fruitworm (Lcpidoptcra: Noctuidac). J. Econ Entomol. 84. Y78-986

Zalom, F. G., Wilson, L. T. and Smith, R. (lY83) Oviposition patterns h) several lepidopterous pests on processing tomatoes in California. EWt,. Entomoi. 12. I 133-I I.37

Received 2Y September lYY4 Revised 4 January 1905

Accepted 6 January 1905

Crop Protection 1995 Volume 14 Number 8 687