Section C: Chemical Control, Biopesticides, Resistance Management, and Application Methods (Part Two) - 1999
Affiliation & Location: 1 UC Cooperative Extension, UC Desert Research and Extension Center, Holtville, CA, USDA-ARS, 2 Western Cotton Research Laboratory, Phoenix, AZ, and 3 USDA-ARS, Cotton Quality Research Laboratory, Clemson, SC.
Research & Implementation Area: Section C: Chemical Control, Biopesticides, Resistance Management, and Application Methods.
Dates Covered by the Report: March - December 1998
Silverleaf Whitefly Control In Cotton, 1997
A stand of cotton, var. DPL 5415, was established at UC Desert Research & Extension Center 25 March 1998. Fourteen insecticide treatments and an untreated control were replicated four times in a randomized complete design. Insecticide treatments were as follows: Applaud 70 WP at 0.35 lb ai/a applied 7 and 21 July followed by Danitol 2.4 EC at 0.2 lb al/a plus Orthene 90S at 0.5 lb ai/a applied 4 August, Applaud 70 WP at 0.35 lb ai/a plus Phaser 3EC at 0.75 lb ai/a applied 7 and 21 July followed by Danitol 2.4 EC at 0.2 lb al/a plus Orthene 90S at 0.5 lb ai/a applied 4 August, Applaud 70 WP at 0.35 lb ai/a plus Decis 02. EC at 0.02 lb ai/a applied 7 and 21 July followed by Danitol 2.4 EC at 0.2 lb al/a plus Orthene 90S at 0.5 lb ai/a applied 4 August, Ovasyn 1.5 EC at 0.25 lb ai/a plus Phaser 3 EC at 0.75 lb ai/a applied 7, 14, 21, 28 July and 4 August, Knack 0.86 EC at 0.05 lb ai/a applied 7 July followed by Ovasyn 1.5 EC at 0.25 lb ai/a plus Phaser 3 EC at 0.75 lb ai/a applied 21, 28 July and 4 August, Danitol 2.4 EC at 0.2 lb al/a plus Orthene 90S at 0.5 lb ai/a, EXP61486A 70 WP (acetamiprid) at 0.022 lb ai/a, EXP61486A 70 WP at 0.044 lb ai/a, EXP61486A 70 WP at 0.075 lb ai/a, EXP61486A 70 WP at 0.1 lb ai/a, TADS12222 1.67 EC (acetamiprid + fipronil) at 0.044 lb ai/a, TADS12222 1.67 EC (acetamiprid + fipronil) at 0.088 lb ai/a, and AVA CHEM. Sugar ester at 0.3% AI w/v in water. All insecticide treatments were applied 7, 21, 28 July and 4 August unless otherwise designated. Helena Buffer PS at 23.6 ml/5 gal. and Sylgard 309 at 5.9 ml/5 gal. were used with all insecticide spray treatments. Silverleaf whitefly adults were sampled from ten plants at random in each plot via the leaf turn method using the fifth main stem leaf from the terminal on 10, 22, 29 June, 6, 13, 20, 27 July, 3, 11 August 1998. Silverleaf whitefly eggs and nymphs were counted on 1.54 cm2 leaf disks from 5th position, main-stem terminal leaves extracted from ten randomly selected plants in each plot on the same dates adult whiteflies were sampled. Seed cotton was hand picked from 0.002 acre per plot and yield data were recorded on 28 August 1998. Seed cotton samples were ginned at the USDA-ARS Western Cotton Research Laboratory in Phoenix, AZ and lint samples were sent to the USDA/ARS Cotton Quality Research Station in Clemson, SC for stickiness and sugar analysis.
The nymphal means for the sugar ester treatment was not different than the untreated control on any of the sampling dates. The EXP61486A, TADS1222, and Danitol + Orthene treatments provided the highest levels of control for silverleaf whitefly adults and nymphs with means lower than the untreated control on all post-treatment sampling dates for both adults and nymphs, p # 0.05. There were no differences among treatments for seed cotton yields.
Affiliation & Location: UC Cooperative Extension, UC Desert Research and Extension Center, Holtville, CA.
Research & Implementation Area: Section C: Chemical Control, Biopesticides, Resistance Management, and Application Methods.
Dates Covered by the Report: September 1997 - January 1998
Evaluation of Selected Insecticides for Silverleaf Whitefly Control in Iceberg Lettuce
Iceberg lettuce var. Desert Queen was sown at UC Desert Research & Extension Center 16 September 1997. Four insecticide treatments and an untreated control were replicated six times in a randomized complete design experiment. Insecticide treatments were as follows: Admire 2F at 0.25 lb ai/acre injected 3 inches below the seed-line pre-plant, Applaud 70 WP at 0.25 lb ai/acre, Applaud 70 WP at 0.38 lb ai/acre, Applaud 70 WP at 0.38 lb ai/acre plus Phaser 3 EC at 0.75 lb ai/acre. Foliar sprays were applied on 9, 15, 22 & 29 October, and 5 November, 1997. Silverleaf whitefly, Bemisia argentifolii, were sampled by counting adults via leaf turn on ten plants at random from each plot on, 1, 14, 20 & 28 October and 3 & 11 November, 1997. Silverleaf whitefly eggs and nymphs were counted on 2.54 cm2 of leaf surface from basal leaves of ten plants at random from each plot on 1, 14, 20, & 28 October, and 3 November, 1997. Mature marketable lettuce heads per 0.002 acres per plot were harvested and weighs were recorded in pounds.
The seasonal mean values of adult silverleaf whitefly for the untreated control were greater than all insecticide treatments except Applaud 70 WP at 0.25 lb ai/acre, p # 0.05. The seasonal mean of silverleaf whitefly nymphs for the untreated control was greater than all of the insecticide treatments on 28 October. There were no differences among treatments for seasonal means of silverleaf whitefly nymphs. There were no differences among the treatments for numbers of lettuce heads or weight of lettuce heads.
Affiliation & Location: 1Joint affiliation: Texas Agricultural Experiment Station and USDA-ARS, Beneficial Insects Research Unit, Weslaco, TX; 2formerly with Mycotech Corp., Butte, MT; 3USDA-ARS, Beneficial Insects Research Unit, Weslaco, TX; 4Texas Agricultural Experiment Station, Weslaco, TX, presently with Mycotech Corp.
Research & Implementation Area: Section C: Chemical Control, Biopesticides, Resistance Management, and Application Methods.
Dates Covered by the Report: September 1997 - February 1998
Field Evaluation of the Particle Films M-96-018 and M-97-009 for Whitefly Control on Bell Peppers and Collards
Trials were conducted in Weslaco, TX, to evaluate two particle films for control of Bemisia argentifolii on bell peppers, Capsicum annuum L. `Capistrano', and collards, Brassica oleracea acephala DC. Individual plots consisted of six rows of bell peppers or collards arranged in single-row (peppers) or double-row (collards) beds, at 40-inch spacing, 60-ft in length with a 10-ft buffer between plots. Three replicated plots for each of two treatments and two controls were included in a randomized complete block design. The treatments were M-96-018 Hydrophobic Particle Film and M-97-009 Hydrophilic Particle Film. M-96-018 (25 pounds/acre) was stirred in 98% methanol and M-97-009 (25 pounds/acre) in the spray adjuvants Pinene II (peppers trial) or M03 (collards trial), prior to mixing with water (4 gallons of methanol or 14 ounces of Pinene II or 1 pint of M03 per 100 gallons of water). An untreated control and an adjuvant control were included in each trial. Applications were made using a high pressure hydraulic sprayer with three (peppers) or four (collards) drop nozzles (Lilac Albuz) per bed, at 200 (peppers) or 400 (collards) psi pressure and 100 gpa application volume. Treatments in the peppers trial were applied on 10 and 17 September; and 1, 7, and 15 October. Treatments in the collards trial were applied on 9, 16, 23, and 30 December, and 6, 20, and 27 January. Weekly evaluations (1 day before spray applications and again one week after the last spray application) were made by counting live whitefly immatures (unhatched eggs + nymphs + pupal cases) in one circular area (2 cm2) of leaf surface on 10 plants/plot. Differences among treatments were separated using analysis of variance (ANOVA) on log (n + 1) transformation of the population data. Bell peppers were harvested on 3 and 10 December from one full, 13. 1-feet long section in the four middle beds of each plot. Collards were harvested on 10 February from one full, 10-feet long row section in the four middle beds of each plot. Weight (peppers) and bundles (collards; one bundle is made from one large up to three small plants per bundle, damaged and soiled leaves removed) values were transformed to corresponding log values before ANOVA. Back-transformed data are presented.
Pre-treatment populations of whitefly immatures on bell peppers were high (overall mean 137.3 immatures per 2 cm2 of leaf surface). There were no significant differences in numbers of whitefly immatures among treatments and controls in the pretreatment (P = 0.925) and subsequent counts (all P >0.05). Populations gradually at a similar rate in all treatments and controls to a low overall mean of <1 immature per 2 cm2 on 22 October. Although there were no significant differences in yields among the two treatments and two controls (P = 0.295), the plots treated with M-96-018 and M-97-009 yielded an average of 1,666 and 1, 125 more pounds of marketable bell peppers per acre than the untreated control plots (6,542 pounds per acre), respectively.
Whitefly pressure was low in the collards trial (overall mean 2.4 immatures per 2 cm2 of leaf surface in the pre-treatment counts). There were no significant differences in populations of whitefly immatures among treatments and controls in the pre-treatment (P = 0.324) and subsequent counts (all P >0.05). Whitefly populations remained low in all treatment and control plots during the entire season. No significant differences in yields were found among the two treatments and two controls. However, the plots treated with M-97-009 yielded 1,531 more bundles of marketable greens per acre than the untreated control plots (13,338 bundles per acre).
Affiliation & Location: Joint affiliation: Texas Agricultural Experiment Station and USDA-ARS, Beneficial Insects Research Unit, Weslaco, TX;2 USDA-ARS, Beneficial Insects Research Unit, Weslaco, TX, formerly with Mycotech Corp., Butte, MT; 3USDA-ARS, Beneficial Insects Research Unit, Weslaco, TX.
Dates Covered by the Report: Spring 1998
Field Evaluation of Mycotrol® (Conidia of Beauveria bassiana Strain GHA), Blastospores of Paecilomyces fumosoroseus Strain 612, the Particle Film M97-009, and One Sugar Ester for Control of Whiteflies on Melons
Individual plots, at Weslaco, TX, consisted of 4 beds of cantaloupe melon (Cucumis melo L.) `Perlita' planted on 5 March in 80-inch single-row beds, 45-ft in length with a 8-ft buffer between plots. Three replicated plots for each of 9 treatments and 1 untreated check were included in a completely randomized experimental design. The plots received one of the following treatments: Mycotrol 22WP @ 1x1013 conidia/acre + the adjuvant Silwet® L77 (0.04%); Mycotrol 22WP @ 1x1013 conidia/acre; M97-009 @ 25 lbs/acre + the adjuvant M03 (0.125%); Mycotrol ES9505 @ 1x1013 conidia/acre; air-dried blastospores of Paecilomyces fumosoroseaus formulated in diatomite @ 1x1013 blastospores/acre + the adjuvant Silwet L77 (0.04%) [the rate was 5x1012 blastospores/acre on 6 May]; tank mix of Mycotrol ES @ 1x1013 conidia/acre + M97-009 @ 25 lbs/acre + the adjuvant M03; one sugar ester (technical) @ aqueous 0.3% solution/acre; Mycotrol ES @ 1x1013 conidia/acre; Mycotrol ES @ 1x1013 conidia/acre + the adjuvant Silwet® 560 (5% v/v of Mycotrol ES); or untreated check. Applications of Mycotrol and Mycotrol\M97-009 were made using a high pressure hydraulic sprayer with 3 (first 2 sprays), 5 (next 3 sprays) or 7 (last spray) drop nozzles (Lilac Albuz) per bed, at 400 psi pressure and 14 (3 nozzles), 22.5 (5 nozzles) or 31.5 (7 nozzles) gpa application volume. These treatments were applied on 15, 22 and 29 April; and 6, 13 and 21 May. M97-009 was applied on the above dates, using the above sprayer, number of nozzles per bed and pressure, but at 100 gpa application volume. The sugar ester treatment was applied only on 15 (3 nozzles) and 29 (5 nozzles) April and 13 (5 nozzles) May using the above sprayer, pressure and application volumes. Blastospores were applied on the same dates as the Mycotrol treatments, but using a motorized knapsack mistblower (Solo Master 412) delivering 45 gpa; both sides of each bed were sprayed. Evaluations were made by counting living Bemisia argentifolii nymphs (all 4 instars plus pupae)/unit area (2 cm2 leaf area) on 10 plants in the center of each plot on 14 (precount), 21, and 28 April, and 5, 12, 19 May and 26 May. Differences among treatments were separated using one-way ANOVA on log (n + 1) transformation of the population data and the Tukey HSD test. Untransformed means are presented. Abbott's percent efficacy was calculated for each treatment.
Whitefly pressure was moderate in this trial. There were significant differences in living whitefly nymphs among treatments and control in the precounts taken on 14 April (P = 0.008). The Mycotrol ES/Silwet 560 treatment had significantly more nymphs than did all other treatments and untreated check; the Mycotrol 22WP treatment and the untreated check had significantly fewer nymphs than did all other treatments. Immature whitefly populations increased in all of the plots during the first week of the trial. There were significant differences among treatments on the last day of sampling, 26 May (P < 0.001). The seasonal treatment effects on immature whiteflies were examined through analysis of the integrated population curves for this life stage. The differences in the areas under the treatment curves (not shown) best represent whitefly pressure. Based on seasonal means, there were clear treatment differences in living immature whiteflies (P < 0.001). The seasonal densities of whitefly nymphs (Tukey test) [and respective seasonal Abbott's percent efficacies of treatments in reducing nymphal populations] were: Mycotrol 22WP/Silwet L77 - 37.0 (bc) [39.4%]; Mycotrol 22WP - 37.5 (ab) [38.4%]; M97-009/MO3 - 34.5 (ab) [43.5%]; Mycotrol ES9505 - 35.8 (b) [41.4%]; P. fumosoroseus blastospores/Silwet L77 - 19.7 [67.7%]; Mycotrol ES/M97-009/MO3 - 46 (ab) [23.7%]; sugar ester - 32.1 (b) [47.6]; Mycotrol ES - 27.9 (bc) [54.3%]; Mycotrol ES/Silwet 560 - 41.5 (ab) [32. 1%]; and untreated check - 61.1 (a). Of all the treatments applied to melons against immature whiteflies, P. fumosoroseus blastospores proved to be significantly more effective than parallel treatments and much more effective than no treatment.
Affiliation & Location: USDA-ARS, Beneficial Insects Research Unit, Weslaco, TX; Universidad Autonoma de Nuevo Léon, Facultad de Ciencias Biológicas, Monterrey, Mexico.
Dates Covered by the Report: Fall and Winter 1998
In Vitro and In Vivo Compatibility of Selected Fungicides with Fungal Pathogens of Bemisia Whiteflies
Formulated fungicides tested were chlorothalonil [Bravo 6.0 flowable (F)], propionazole [Tilt 4.17 F], azoxystrobin [Quadris 2.08 F], and sulfur-tribasic copper sulfate [Top Cop 6.25-1.0 F]. Rates [kg (AI)/ha] were: chlorothalonil 1.67, propionazole 0.14, azoxystrobin 0.09, and sulfur-tribasic copper sulfate 3.47.
In Vitro Bioassay. Fungicides were mixed in Sabouraud dextrose agar to equivalent field rates. One fungal plug (1 cm diam.) consisting of mycelia only was transferred to the center of a Petri dish (10 dishes per treatment and control). Dishes were incubated at 25ºC and 16:8 (L:D) h. The dishes of each treatment and control were incubated in isolation because volatile products or by-products could influence fungal growth on other treatment or control dishes. Radial growth was measured daily for 7 d. The 7-d cumulative growth data were analyzed by one-way ANOVA. After the 7-d incubation period, B. bassiana radial growth was 38.5 mm in the controls and 3.5, 4.4, and 11. 3 mm on the Bravo, Quadris, and Top Cop treated agar, respectively. No growth occurred on the Tilt-treated agar plates. Treatment effects were significantly different (P <0.001). P. fumosoroseus radial growth at day 7 was 37.4 mm on the control plates, 0 mm on the Tilt plates, and 7.7, 8.6, and 26.8 mm, on the Bravo, Quadris, and Top Cop plates, respectively (P <0.001). We transferred the mycelial plugs from the Tilt treatments to untreated agar plates and examined them for 7 d for any sign of regrowth. No regrowth occurred. We concluded that Tilt was fungitoxic and that the other fungicides were moderately to strongly fungistatic to both fungi.
Spray Chamber In Vivo Bioassay. A laboratory spray chamber, calibrated to deliver 282 liters/ha using 3 TXVS-6 nozzles (2 on drops) at 2.2 kg/cm2, and 4.8 km/h, was used to apply fungicides to whitefly-infested melon leaves (30 early 3rd instar nymphs per leaf; 4 replicated leaves per treatment), either 2 days before [2DB], on the same day (3 h before the fungi) [SD], or 2 days after [2DA] spray application of spore (aerial conidia) suspensions of B. bassiana and P. fumosoroseus. On SD, each leaf was sprayed with one 2-ml aliquot of spore suspension using a Potter spray tower. Each spore suspension was sprayed at a pressure of 0.7 kg/cm2 using the fine spray nozzle (0.25 mm orifice diameter) provided with the tower. Dosages, estimated from spore counts taken from cover slips placed alongside the leaves in the spray arena of the Potter tower, were 808 ± 86 and 752 ± 188 spores/mm2 for B. bassiana and P. fumosoroseus, respectively. Treated and control (0.01 % aqueous Tween 80) leaves were then isolated individually in vented plastic Petri dishes, and incubated for 24 h at 25ºC and 100% RH under a photophase of 16:8 (L:D) h. Thereafter, leaves were maintained under similar temperature and light regimes, but at 50-55% RH. The dishes of each treatment and control were incubated in isolation for the reason given above. Whiteflies were scored for mycosis 7 days after spore application. The angular values of proportion mycosis were analyzed by one-way ANOVA. Means were separated using the Tukey HSD test. Untransformed means are presented. In the P. fumosoroseus series, control mycosis (95.4%) was higher but not significantly different from mycosis in the 2DB, SD and 2DA Top Cop (P = 0.598), the 3 Quadris (P = 0.077), and the 3 Tilt (P = 0.057) treatments. Mycosis rate was 71.7, 49.1, and 65.8% in the 2DB, SD, and 2DA Bravo treatments, respectively [P = 0.007; Tukey test: control (a), 2DB (ab), SD (b), 2DA (b)]. In the B. bassiana series, control mycosis (81.2%) was significantly higher than mycosis in any of the 3 Bravo [P <0.001; Tukey test: control (a), 2DB (26.7%b), SD (18.3%b), 2DA (45.0%b)] and any of the 3 Tilt [P <0.001; Tukey test: control (a), 2DB (57.5%b), SD (41.7%b), 2DA (40.8%b)] treatments. Significant differences also were found in the Quadris treatments [P = 0.001; Tukey test: control (a), 2DB (65.8%ab), SD (63.3%bc), 2DA (45.8%c)] and in the Top Cop treatments [P = 0.005; Tukey test: control (a), 2DB (38.3%b), SD (48.3%b), 2DA (60.8%ab)]. At all 3 times of application, the fungicides were generally more compatible in vivo with P. fumosoroseus than with B. bassiana.
Affiliation & Location: USDA-ARS, Beneficial Insects Research Unit, Weslaco, TX.
Dates Covered by the Report: Fall 1998
Effects of Beauveria bassiana and Paecilomyces fumosoroseus on Two Lines of Bemisia whiteflies Both Reared on Two Different Host Plants
Two lines (one from Arizona [AZ] and one from Texas [TX]) of Bemisia whiteflies were each reared in greenhouses for 6 generations on cotton `Sure Gro 125' and cantaloupe melon `Explorer'. Beauveria bassiana (strain GHA) and Paecilomyces fumosoroseus (strain 613) were applied to host plants infested with early 2nd-instars from the four cultures [AZ melon, AZ cotton, TX melon, and TX cotton] as 1-mi aliquots of conidial suspensions by using a Potter spray tower. Each test measured the effects of 3 dosages (rates) of conidia of each fungal strain using 3 replicated leaves per dosage (3550 2nd-instars per leaf). Three replicated carrier (0.01% aqueous Tween 80) controls were included with each treatment. Following spray applications, the leaves were incubated at 25ºC, 50% RH and a 16 h photoperiod and were monitored daily for 10 d for whitefly mortality. The Abbott correction for control mortality was not used because only mycosis, not total mortality, in the 2nd instars was considered. Proportions of mycosis in the eight funguswhitefly culturehost plant combinations were arcsin square root transformed prior to ANOVA. When dosage effects in any of the 8 combinations were significant, means were separated using Tukey HSD test. Untransformed means are presented. Probit analysis was used to estimate the eight 10-d LD50 values (conidia/mm2), and other regression parameters.
B. bassiana. There was no dosage effect on mycosis rates in the nymphs from the AZ cotton culture (P = 0. 145; 49.2% mycosis at high dosage [940 conidia/mm2]), nor in nymphs from the TX cotton culture (P = 0.735; 47.6% mycosis at high dosage). Mycosis rates were 31.2 (Tukey test: b), 55.0 (b) and 83.9 (a)% in nymphs from the AZ melon culture at the low, medium and high dosage, respectively (P = 0.004). No dosage effect was found in the mycosed nymphs from the TX melon culture (P = 0.093; 72.5% mycosis at high dosage). The 10-d LD50 values were I fold lower (=67 conidia/mm2) in both melon series than in both cotton series (»934 conidia/mm2). Judged by the overlap between the confidence limits of the LD50 values in both melon and both cotton cultures, the two lines of Bemisia nymphs were equally susceptible to B. bassiana when reared on either host plant. The lack of overlap among the melon and cotton LD50 values indicated that both the AZ and TX lines of Bemisia were less susceptible to B. bassiana infection when reared on cotton than when reared on melon.
P. fumosoroseus. Only 28.5 (AZ cotton) and 12.1% (TX cotton) of nymphs died from mycosis after exposure to the high dosage (893 conidia/mm2) of the fungus. No dosage effect was found in either series (AZ cotton: P = 0.413; TX cotton: P = 0.076). Mycosis rates in the AZ melon culture were 37.7 (Tukey test b), 71.1 (ab) and 82.8 (a)% at the low, medium and high dosage, respectively (dosage effect: P = 0.04). In the TX melon culture, the rates were 31.0 (b), 67.3 (a) and 88.3 (a)% at the low, medium and high dosage, respectively (dosage effect: P = 0.006). The 10-d LD50 values for AZ melon and TX melon were 74 and 91 conida/mm2, respectively and were not significant different (overlap of confidence limists). The two lines of Bemisia nymphs were therefore equally susceptible to P. fumosoroseus infection. The LD50 values for AZ cotton and TX cotton could not be calculated, but were estimated to be >4,000 and >39.000 conidia/mm2, respectively, which indicated that Bemisia reared on cotton was not susceptible to P. fumosoroseus.
We concluded that there was no line effect, but a strong host plant effect on B. bassiana and P. fumosoroseus pathogenicity to Bemisia nymphs. We hypothesize that gossypol or other allelochemical(s) might have been involved in antimicrobiosis on cotton leaves. The hypothesis is being tested.
Affiliation & Location: 1Department of Entomology, University of California, Riverside, 2USDA, ARS, Western Cotton Research Lab, Phoenix, AZ.
Dates Covered by the Report: January - September, 1998
Effect of Neem, Urea and Amitraz on Oviposition and Immature Development of Bemisia argentifolii (Homoptera: Aleyrodidae)
The effect of two formulations of neem seed extract, a crude extract from India and Azatin, a neem-based insecticide, urea and a mixture of neem seed extract + urea, were investigated as oviposition suppressants and larvicides against Bemisia argentifolii Bellows & Perring. Both seed and soil applications to cotton were tested. Pre-treatment of cotton seeds by neem seed extract did not significantly suppress oviposition but it was suppressed when it was applied as a soil treatment. However, both seed and soil applications of neem seed extract produced significant mortality of immatures leading to reduced emergence of adults. Azatin was effective in suppression of oviposition as well as in inducing larval mortality by both methods of application. Treatment of cotton seeds by urea was effective in reducing oviposition but was ineffective in a soil application. Although treatment of seeds or soil by urea was not toxic to immatures by itself, a mixture of neem seed extract + urea was more effective in the suppression of oviposition and immature mortality, thus reducing the numbers of adult whiteflies that emerged.
Foliar applications of neem seed extract and Amitraz, a non-chlorinated formamadine, were investigated in another series of tests of their effects on oviposition and development of whitefly immatures. Both compounds effectively suppressed oviposition and induced mortality of immatures. Ovicidal activity of Amitraz appeared to occur late in embryonic development, or even post-embryonically during eclosion. These results suggest that neem or Amitraz may serve as alternative chemicals to conventional insecticides in a resistance management program for whiteflies.
Affiliation & Location: University of Florida, Southwest Florida Research and Education Center, Immokalee FL 32142.
Dates Covered by the Report: March - June 1998
Control of Silverleaf Whitefly and Turnip Aphid on Collards with Foliar and Soil-Applied Systemic Insecticides
The grower may have the option to apply systemic insecticides to the foliage or the soil. The objective of this study was to compare the efficacy of these two application methods against the silverleaf whitefly (SLF). Two sets of 3 of fertilized beds 32 inch wide, 240 ft long were fumigated with 67/33% methyl bromide/chloropicrin, covered with black polyethylene film and drip irrigated. The 2 sets of 3 rows were separated by a 15 ft drive middle and the middle row of each set was planted with collard seedlings on 12 January as a source of pest inoculum. Greenhouse raised collard seedlings were planted in the remaining 4 beds at 18-inch spacing on 13 February. Each bed was divided into 7 plots 34 ft long to which 6 treatments and untreated check were assigned in a RCB design with 4 replications. Soil treatments were applied in 10 ml water to each plant hole on 06 Mar. Foliar treatments were initiated 28 April with a high clearance sprayer utilizing a hydraulic pump operating at 200 psi and delivering the spray at a rate of 33 GPA through one drop boom on each side of the row and one overhead, each equipped with 1 yellow hollow cone Albuz7 nozzle. These applications included 2 of CGA-215 and CGA293 on 28 Apr and 15 May and 6 each week of acetamiprid and Provado beginning 28 Apr.. Silwet at 0.25% V/V was added to the tank with all sprays. Aphids and adult whiteflies were sampled in soil-treated and check plots on 2 whole leaves (one upper 18 x 25 cm and one lower 29 x 34 cm, April 7 and 20 respectively) on each plant, 10 plants/plot. Most aphids were found on the upper leaf and whiteflies on the lower leaf. Sampling for adult whiteflies in all plots began 01 May using a 9 X 13 inch metal cake pan (Abeat pan@) painted black and covered with a 10% detergent/vegetable oil mixture. Total number of adults captured from three beats on one side of 3 separate plants was counted as a sub-sample with 4 sub-samples collected/plot. Immature whiteflies were counted under a stereoscopic microscope in the laboratory on 4 leaves (1,000cm2)/plot collected from the field on 05 May and 14 May. Also on 14 May spider mite infestation was evaluated on 4 leaves/plot by rating on a scale of 0 to 3 where 0 indicated no mites, 1 indicated 1-15, 2 indicated 16-45, and 3 indicated 45> were counted/leaf.
Turnip aphids were present on 7 April but disappeared later following the appearance of numerous coccinellids.
Both aphid and whitefly numbers were significantly lower in soil-treated plots on 7 April compared to the check with
no significant difference between treatments. The same pattern was seen with whiteflies on 20 April. On all
subsequent dates, fewer whitefly adults were observed on treated plants in all plots compared to the check except on 04 June
for plants treated with CGA-215. There were never any significant differences between soil treatments in number of
adults although the overall mean was slightly lower with Admire. Neither were there any significant differences between
foliar CGA-293 and acetamiprid although the overall mean for the latter was numerically lower. CGA-215 provided the
least protection against adults, significantly less than acetamiprid on 5 sample dates and overall dates. Acetamiprid
provided significantly better control of adults than Provado on 2 sample dates, and fewer adults were seen on plants sprayed
with Provado compared to CGA-215 on one sample date. Fewer adults were seen plants treated by soil application
compared to foliar application through14 May (68 DAT) and there were still significantly fewer adults soil-treated plants
through 17 June (103 DAT) than the control. On 5 May, fewest eggs or small nymphs were seen on plants treated with
CGA-293 and Admire, though not significantly less than all other treatments except Provado and the check (eggs) or the
same two and acetamiprid (small nymphs). On that date fewest large nymphs and pupae were seen on plants treated
with Admire, though not significantly less than other treatments except the check and Provado (pupae) or Provado
and acetamiprid (large nymphs). No eggs or small nymphs were found on Provado or CGA-293 soil-treated plants on
14 May and all treatments had fewer eggs than the check except for CGA-215. Fewer large nymphs as well were seen
on all treated plants compared to the check except for CGA-215, and there were no pupae on Admire-treated
plants although differences were not significant except for the untreated check. The proportion of large nymphs and pupae
that were parasitized was not diminished by any treatment, and might have been enhanced although differences were
not significant. Spider mites were not significantly affected by any treatment. In summary, imidacloprid provided
excellent control of both adult and immature whiteflies when soil-applied but did not function well when applied to the plant.
CGA-293 functioned well in both modes, comparable to Admire when soil-applied and to acetamiprid when applied as
a foliar. These results were largely consistent with those obtained last year on tomato.