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Section C: Chemical Control, Biopesticides, Resistance Management, and Application Methods (Part One) - 1999
Authors: J. R. Brazzle1, N. Toscano2 and P. Goodell3 Affiliation & Location: 1 University of CA Cooperative Ext., Kern County, CA; 2 University of CA, Riverside, CA; 3 University of CA, IPM, Parlier, CA; Implementing a resistance management program for Bemisia argentifolii: Building the necessary bridges Summarized by T. J. Henneberry Dr. Brazzle suggested that successful management of silverleaf whitefly in the San Joaquin Valley is dependent upon IPM, resistance management and hard work. Chemical tools [particularly the use of the insect growth regulators (IGRs)] are an integral part of the whitefly management program. The efficacy of these products depends upon a good scouting program, use of the action thresholds and judicious application of each tool. A high quality program includes cultural management techniques tailored on a regional basis. In the SJV a high premium should be placed on host plant sanitation, cotton management and intensive scouting to assist in good decision making. Investigator's Name(s): D. H. Akey, T. J. Henneberry, & C. C. Chu.
Affiliation & Location: USDA, ARS, Western Cotton Research Laboratory, Phoenix, AZ 85040.
Research & Implementation Area: Section C: Chemical Control, Biopesticides, Resistance Management, and Application Methods.
Dates Covered by the Report: June 1993 - October 1998
Ground Application Techniques That Improved Under-Leaf and Inner Canopy Coverage Cotton: Development and Testing of Hydrostatic Sprayers-Transition from Experimental to Farm Equipment
We increased hydrostatic spray efficiency, by using a gasoline driven single cylinder piston pump that delivered spray pressures > 450 psi on a JD 600 Hi-Cycle. The pump vibrated but a replacement "5-frame" 3 cylinder pump (Cat Pump model 390) ran evenly. It had an output to 12 gpm, a 600-psi rating., but exceeded 700 psi. Studies were conducted at 100 and 400 psi and at 30 and 60 gal/ac. Upper and lower leaf surfaces were tested for coverage at nodes 5, 7, and 9 from top terminal. Coverage was determined by: sprayer application with dyes, a 1% solution of Leucophor EFR Liquid (Sandoz Chemical Corp., Charlotte, NC) and powered sodium fluorescein); ultraviolet color photography of leaf samples 10-12 hr after sampling; and digitalization by video to obtain % coverage, droplet pattern, and size. The piston pumps required priming and was damaged if it run dry. We used the JD 600 Hi-Cycle centrifugal pump to provide a 35 psi prime pressure to the piston pump. The system was shut down immediately if the spray tank emptied or flow ceased. Diaphragm pumps are not prime dependent for structural integrity. We tested a gasoline driven inline medium diaphragm pump (Udor, model Kappa 55) with a 15gal output and 560-psi rating. In 1995-96, a JD 6200 and 6400 tractor (4-WD, high clearance wheels, enclosed cabs and filtered air) were each fitted with: a PTO-driven Kappa 55 diaphragm pump, 47 ft boom (14 rows of 40-in cotton), 8 15-gal spray tanks, 65-gal rinse tank, and for the JD 6400, a 250-gal main tank. Until these units were ready, we used a JD 6000 sprayer with a 3-nozzles/row boom. We tested 40 and 70 psi. in 1995 but with only 15 gal/ac in a large area test. Plots were 5ac and set on a 2-fallow, 6-row plant scheme. The 70 psi applications covered better than 40 psi but were not significantly different in yield nor lint stickiness. High clearance needs were removed by driving through fallow rows. Irrigation water breaking through into one fallow row but not the other was a serious problem. The tractor sank on one side but not the other causing the boom to tilt. One end dipped in cotton, the other raised above it. In 1996, hydraulic rams were installed to tilt-level the booms keeping the left and right sections parallel. In 1997-98, we evaluated distributor-available spray components. We used in-cab control panels to activate application and rinse tanks, boom sections, and pressure. One tractor had radar, and accurate ground speed proved useful. Solenoid valves, rated at 300 psi at 90o F, were used at 250 psi to offset for higher summer temperatures. Brass or bronze spray parts and fittings were replaced with shelf-available plastic parts that worked at 250 psi but needed double-gaskets on drops and daily tightening of plastic swivel bodies. Ground is superior to aerial application for many biorational agents, e.g., the fungi, Beauveria. Aerial application is fine for agents with translaminar, vapor, or high toxicity activity. Disadvantages to ground application include: driving time, labor and fuel costs, and chances of weather disruption. Increased scheduling problems may occur with irrigation timing; necessary for dry fields for ground sprayers in solid-plant fields or in soils where water can permeate across beds and berms. Tractors can be used in place of high-clearance spray rigs. We had success with 4-WD tractors equipped with booms that can be leveled and have large vertical adjustment for crop height. Drops that placed small droplets in the canopy reduced drift problems. Drops allowed positioning nozzles between rows to angle spray into canopy under story permitting spraying in windy conditions that would curtail use of broadcast booms because of drift and inefficient spraying. Droplet sizes of 70-150m formed a mist in the canopy and remained trapped in it until impinging on foliage, in contrast to drifting across and down rows.
Plastic parts reduce cost and are available from spray part distributors. However, the metal and 600 psi-hose component system remained the most reliable and dependable. Some metal components have been used for 8 years; for safety, we change hose components yearly. Our studies show that greater volumes (30 > 15 gal) are the most important parameter in increasing spray efficiencies, followed by pressure increases (250>100-70>40 psi).
Investigator's Name(s): D. H. Akey & T. J. Henneberry.
Affiliation & Location: USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ 85040.
Research & Implementation Area: Section C: Chemical Control, Biopesticides, Resistance Management, and Application Methods.
Dates Covered by the Report: June - October 1998
A Sugar Ester (AVA Chemical Ventures, L.L. C.) as a Biorational Agent Against the Silverleaf Whitefly, Bemisia argentifolii, in Field Trials in Upland Cotton in Arizona
Deltapine NuCOTN 33B was planted and furrow irrigated in plots 109 ft. in length and 12 rows across (40-in. rows). Plots were separated by 4 fallow rows and 20 ft alleys. A sugar ester (AVA Chemical Ventures, L. L. C.) was used at 0.2 and 0.3%wt/v gal/ac. Applications were made once the silverleaf whitefly reached the action threshold (Univ. AZ recommendations). This treatment was part of a 12-treatment random block design that included a "Best Agricultural Practice regime" (BAP), embedded controls, and a 1-ac block control.
Eggs, small nymphs, and large nymphs were sampled from leaves taken from 5 plants per plot, from the fifth main-stem leaf down from the first expanded terminal leaf. Each sample was counted from a 1-in. disk taken between the main leave stem and the next lateral vein. Adults were sampled from 30 leaves/plot, same location using a binomial decision of counting a leaf as positive if 3 or more adults were present. This indicated a presence of 5 adults on the 5th leaf per plant. Weekly sweeps were taken in all plots for predators, parasites, and Lygus. Applications were made by ground with 5 nozzles/row, 1 overhead, and 2 swivel nozzles angled upward on a drop on each side of the row. Sprays were applied at 250 psi and 30 gal./ac.
The 1998 cotton season was a poor production year. The SLWF population reached action threshold (Univ. AZ) between July 27- Aug.6, 1998. Two sprays were applied (8-day period, then the SLWF populations dropped precipitously and did not recover before the end of the cotton season. Sugar esters at 0.2 and 0.3 % wt/v gal/ac had efficacies against immatures as follows: eggs, 42, 43 %; small nymphs, 2, 32 %; and large nymphs, 10, 63 %, respectively. Despite these low efficacy rates for eggs and small nymphs, for the 0.3% rate for the sugar ester, the SLWF populations remained below action thresholds. Only egg efficacies were statistically significant by ANOVA and LSD (P < 0.05). Buprofezin (ApplaudTM 70 WP, AgrEvo, 0.35 lb. AI/ac) was the first BAP treatment was to be applied. Because of the unusual nature of the SLWF population decline, no other BAP treatments were made. Buprofezin was used as a standard and had egg, small nymph, and large nymph efficacies of 28, 37, 38 %, respectively. Comparatively, 0.3% sugar ester was as effective at controlling SLWF, especially against reducing numbers of large nymphs. The sugar ester at 0.3% was effective at controlling silverleaf whitefly immature life stages.
Investigator's Name(s): D. H. Akey & T. J. Henneberry.
Affiliation & Location: USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ 85040.
Research & Implementation Area: Section C: Chemical Control, Biopesticides, Resistance Management, and Application Methods.
Dates Covered by the Report: June - October 1998
Azadirachtin (as Bollwhip®), a Biorational Agent Against the Silverleaf Whitefly, Bemisia argentifolii, in Field Trials in Upland Cotton in Arizona
Deltapine NuCOTN 33B was planted and furrow irrigated in plots 109 ft. in length and 12 rows across (40-in. rows). Plots were separated by 4 fallow rows and 20 ft alleys. BollwhipTM(Thermo Trilogy) was used in a 4.5% formulation at 6 oz product /ac. The treatment was part of a 12-treatment random block design that included a "Best Agricultural Practice regime" (BAP), embedded controls, and a 1-ac block control.
Eggs, small nymphs, and large nymphs were sampled from leaves taken from 5 plants per plot, from the fifth main-stem leaf down from the first expanded terminal leaf. Each sample was counted from a 1-in. disk taken between the main leave stem and the next lateral vein. Adults were sampled from 30 leaves/plot, same location using a binomial decision of counting a leaf as positive if 3 or more adults were present. This indicated a presence of 5 adults on the 5th leaf per plant. Weekly sweeps were taken in all plots for predators, parasites, and Lygus. Applications were made by ground with 5 nozzles/row, 1 overhead, and 2 swivel nozzles angled upward on a drop on each side of the row. Sprays were applied at 250 psi and 30 gal./ac.
The 1998 cotton season was a poor production year. The SLWF population reached action threshold (Univ. AZ recommendations) between July 27- Aug.6, 1998. Two sprays were applied (8-day period, then the SLWF populations dropped precipitously and did not recover before the end of the cotton season. Azadirachtin as Bollwhip®) had efficacies against immatures as follows: eggs, 32 %; small nymphs, 35 %; and large nymphs, 77%, respectively. Despite these low efficacy rates for eggs and small nymphs, the SLWF populations remained below action thresholds. Only egg efficacies were statistically significant by ANOVA and LSD (P < 0.05). Buprofezin (ApplaudTM70 WP, AgrEvo, 0.35 lb. AI/ac) was the first BAP treatment was to be applied. Because of the unusual nature of the SLWF population decline, no other BAP treatments were made. Buprofezin was used as a standard and had egg, small nymphs, and large nymph efficacies of 28, 37, 38 %, respectively. Comparatively, Bollwhip® was as effective at controlling SLWF, especially against reducing numbers of large nymphs.
Investigator's Name(s): D. H. Akey & C. C. Chu.
Affiliation & Location: USDA, ARS, Western Cotton Research Laboratory, Phoenix, AZ 85040.
Research & Implementation Area: Section C: Chemical Control, Biopesticides, Resistance Management, and Application Methods.
Dates Covered by the Report: June - October 1998
Acetamiprid as NI 25 Against the Silverleaf Whitefly, Bemisia argentifolii, in Field Trials in Upland Cotton in Arizona
Deltapine NuCOTN 33B was planted and furrow irrigated in plots 109 ft. in length and 12 rows across (40-in. rows). Plots were separated by 4 fallow rows and 20 ft. alleys. Acetamiprid (Rhone-Poulenc, NI-25) was applied at 3 rates of 24.3 g, 36.45 g, and 48.6 g AI/ac. Applications were made once the silverleaf whitefly reached the action threshold (Univ. AZ recommendations). This treatment was part of a 12-treatment random block design that included a "best agricultural practice regime," and a 1-ac block control.
Eggs, small nymphs, and large nymphs were sampled from leaves taken from five plants per plot, from the fifth main-stem leaf down from the first expanded terminal leaf. Each sample was counted from a 1-in. disk taken between the main leave stem and the next lateral vein. Adults were sampled from 30 leaves/plot, same location using a binomial decision of counting a leaf as positive if three or more adults were present. Weekly sweeps were taken in all plots for predators, parasites, and Lygus. Applications were made by ground with 0.5 nozzles/row; 1 overhead, and 2 swivel nozzles angled upward on a drop on each side of the row. Sprays were applied at 250 psi and 30 gal./ac. The 1998 cotton season was a poor production year. The SLWF population reached action thresholds between July 27- August 6, 1998.
Only one spray was applied of each rate, then the SLWF populations dropped precipitously and did not recover before the end of the cotton season. However, acetamiprid was effective at controlling silverleaf whitefly.
Investigator's Name(s): Frank J. Byrne & Nick C. Toscano.
Affiliation & Location: Department of Entomology, University of California, Riverside, CA92521.
Research & Implementation Area: Section C: Chemical Control, Biopesticides, Resistance Management and Application Methods.
Dates Covered by the Report: 1998
In vitro Acetylcholinesterase Inhibition in Bemisia tabaci and its Relevance to Organophosphorus Resistance Expressed in Bioassays
The target site for organophosphorus (OP) insecticides is the nerve enzyme, acetylcholinesterase (AChE). The efficacy of OPs at this target site is primarily governed by their affinity for the active site on the enzyme. In Bemisia tabaci, as in many pest species, modifications to the AChE can confer considerable levels of resistance.
All OP resistant B. tabaci populations express AChE insensitivity as the predominant resistance mechanism. In populations expressing the same insensitive variant, differences in OP resistance levels are likely to be caused by additional mechanisms. However, there is no evidence that these can confer any significant resistance in the absence of target-site insensitivity. Thus, the insensitive AChE will confer a baseline level of resistance. In B. tabaci, a clear correlation exists between the levels of insensitivity measured using in vitro biochemical assays and levels of resistance expressed in toxicological bioassays. However, insensitivity factors can be at least an order of magnitude greater than the resistance factors determined from bioassays. A detailed kinetic analysis of the AChEs in resistant B. tabaci shows that, in addition to the importance of intrinsic insensitivity, differences in affinity for the substrate (acetylcholine, ACh) and the turnover of ACh are extremely important
Despite the knowledge we have on resistance to OPs in B. tabaci, these chemicals are still widely used in management programs designed to control this pest. Furthermore, OPs (and carbamates, which also target AChE) are used in the management of other insects in the pest complex and these treatments could have inadvertent effects on the resistance status of whiteflies through the selection of mechanisms additional to AChE insensitivity, particularly if they confer cross resistance to other insecticide classes.
In California, one form of insensitive AChE has been identified in field populations of B. tabaci. The purpose of this study was to determine the relative potencies of OPs against this enzyme, concentrating on those chemicals which B. tabaci is likely to come into contact with in California agriculture systems. By determining the in vitro effects of OPs at the level of the target-site, it will be possible to identify the most effective compounds for use in field treatments, as well as those which represent a high resistance risk.
Investigator's Name(s): Luko Hilje, Douglas Cubillo, & Guido Sanabria.
Affiliation & Location: Plant Protection Unit, CATIE. Turrialba, Costa Rica.
Research & Implementation Area: Section C: Chemical Control, Biopesticides, Resistance Management, and Application Methods.
Dates Covered by the Report: August 1996 - December 1998
Bitterwood (Quassia amara) Extracts Kill Bemisia tabaci Adults
Bemisia tabaci (Gennadius) is an important pest of several food crops in Mesoamerica and the Caribbean, especially as a geminivirus vector in beans, tomato, and bell pepper. Grower response to its damage has been the overuse of insecticides, sometimes with daily applications, which has increased the risk of insecticide residues on vegetables, water and soil contamination, toxicity to field workers, and substantial reductions in grower's income; in addition, this overuse has fostered the appearance of B. tabaci insecticide-resistant strains, as well as the decline of natural enemy populations of B. tabaci and other crop pests. The importance of these problems justifies the development of insecticides with new modes of action, among which some active principles present in plants offer a good potential, as it currently happens with neem (Azadirachta indica, Meliaceae), seed extracts.
There is a sound possibility with bitterwood, Quassia amara L. ex Blom (Simaroubaceae), which early in the century was one of the classical botanical insecticides, as its wood contains several quassinoids, such as quassin and neoquassin, which are toxic to several homopteran, lepidopteran and coleopteran species. Currently, there is a growing interest in promoting the utilization of this wild shrub as an economic resource for Indian communities in Mesoamerica, so that several of its ecological, silvicultural, and marketing aspects have been investigated in recent years.
In order to test the insecticidal properties of bitterwood against B. tabaci, a greenhouse experiment was set up at CATIE, in Turrialba, Costa Rica. Two bitterwood extracts (aqueous and metanolic) were tested, each one in the following six doses: 5, 10, 15, 20, 25 and 50 ml/l of water (Q05, Q10, Q15, Q20, Q25 y Q50). They were compared to a relative (endosulfan, Thiodan 35% CE, at 0.875 g a.i./ l water) and an absolute control (distilled water). The source solution of bitterwood was prepared from 1.3 kg of wood, as to obtain a final volume of 250 ml. A completely randomized block design was used. The substances were sprayed over bean plants (cv. Negro huasteco), which were placed inside sleeve cages, to which 100 whitefly adults per replicate were released. The number of landed (2, 4 y 24 h later) and living adults (48 h later), as well as deposited eggs were counted.
All the doses of both bitterwood extracts were able to kill whitefly adults. However, the metanolic extracts in general were superior, especially at higher doses (Q20, Q25 and Q50). The highest dose (Q50) did not differ from endosulfan (p£ 0.05), which was the best treatment in terms of reducing landing adult numbers, living adults after 48, and oviposition, excepting that endosulfan killing effect was attained fastest.
Bitterwood extracts seem not to pose risks to people, as they are commonly used as a natural medicine for digestive problems. Nevertheless, their persistence could become a limiting factor for using them on vegetables, because of their very bitter taste to people.
Investigator's Name(s): Rosalind R. James & Gary Elzen.
Affiliation & Location: USDA, ARS, Kika de la Garza Subtropical Agricultural Research Center.
Research & Implementation Area: Section C: Chemical Control, Biopesticides, Resistance Management, and Application Methods.
Dates Covered by the Report: June - December 1999
Integrating the Biocontrol Agent Beauveria bassiana with Imidacloprid
Imidacloprid is a chloronicotinyl analogue of nitromethylene insecticidal compounds, and has been used effectively to control whiteflies in melons and cucumbers. It is applied either as a soil drench (often at the time of planting) or as a foliar spray. Beauveria bassiana is an entomopathogenic fungus, also effective in curcurbits. This biopesticide is applied as a foliar spray using high pressure (400 psi) with drop nozzles directed at the undersides of leaves. B. bassiana usually infects only nymphs.
Combining B. bassiana with imidacloprid has several potential benefits. When imidacloprid is applied as a soil drench at the time of planting, its effectiveness declines during the season, and spray applications of B. bassiana could be used to control Bemisia populations that develop later in the season. Alternatively, B. bassiana and imidacloprid could be applied foliarly together as a tank mix to control nymphs. Applying insecticide after planting allows the grower to wait and see if whitefly populations are going to reach significant levels before money has been spent on treatments. Strategies for combining the biological and chemical pesticides could also be used to manage against the development of whitefly populations that are resistant to imidacloprid. Combining the two pesticides would be most effective if they were synergistic, each enhancing the activity of the other.
We tested for synergy in the laboratory using 21-d old, potted, melon plants. We tested two methods of application. In the first, the two pesticides were sprayed onto plants infested with 3rd instar B. tabaci (B- biotype). Application rates included 1x and 0.5x the field rates, and the pesticides were applied both alone and in tank mixes. In the second experiment, potted plants were soil-drenched with imidacloprid four days prior to being infested with whiteflies. B. bassiana was applied as a foliar spray when the nymphs in the controls reached the 3rd instar. Again, we used full and half field rates, and the treatments were applied alone and in combination in a 2-way analysis of variance design.
Imidacloprid showed no effect on the germination rate or colony formation of B. bassiana on nutrient agar. However, when imidacloprid and B. bassiana were combined for whitefly control, an inhibitory effect was seen. That is, imidacloprid was more effective alone than in combination with B. bassiana. This interactive effect was highly significant (P < 0.0003 for foliar applications of both pesticides; P < 0.0001 for the experiment using the soil drench of imidacloprid).
For example, both pesticides caused a significant decline in the number of insects per leaf. A single application of B. bassiana at field rate caused an 81% decline in whitefly densities, and the imidacloprid drench at field rate caused a 100% decline. When full field rates of each were combined, the population declined 97%. Using the same rate of imidacloprid, but reducing B. bassiana to half rate resulted in greater control, with a 99.3% decline in whitefly densities. Although combining B. bassiana and imidacloprid may give sufficient control, imidacloprid works more effectively alone. Combining these two pest control methods will probably not benefit producers. A reasonable explanation for how B. bassiana can inhibit imidacloprid is being sought.
Investigator's Name(s): Tong-Xian Liu.
Affiliation & Location: Texas Agricultural Experiment Station, Texas A&M University System, 2415 E. Highway 83, Weslaco, TX 78596-8399.
Research & Implementation Area: Section C: Chemical Control, Biopesticides, Resistance Management, and Application Methods.
Dates Covered by the Report: 1998
Management of Bemisia argentifolii with Application of Biorational Insecticides and Imidacloprid on Cantaloupe in Spring in South Texas
The silverleaf whitefly, Bemisia argentifolii, is still the one of most important pests on melons in south Texas. The objective of this study was to develop a season-long whitefly management program for spring cantaloupe with application of insect pathogens and insect growth regulators (IGRs) in the early spring season, and application of imidacloprid (Admire) in the early mid-season to control the whitefly for the remaining season. The materials used included Mycotrol WS (B. bassiana, Mycotech) at 1 lb/ac, Naturalis-L (B. bassiana, Troy Biosciences) at 1 lb/ac; Knack (pyriproxyfen) at 1 lb/ac; Applaud (buprofezin) at 0.35 lb/ac; untreated plots as control. Admire 2F (Imidacloprid, Bayer) was side-injected 56 g [AI]/ac). Cantaloupe seedlings were transplanted in the field on January 22. The plots were arranged in a randomized complete block design with 4 replications. Mycotrol and Naturalis-L were sprayed weekly starting from March 4 to May 11 for 11 weekly applications, and Knack and Applaud, biweekly for 5 applications. Admire was either dripped through the irrigation system at transplanting or side-injected 15 cm deep in the soil on April 14 in the mid-season.
Adult population was high during the entire season. Numbers of adults among the treatments were significantly different during the 12 sampling dates except for the first week that there was no significant difference among the treatments. The treatments with Admire at transplanting had the lowest whitefly population before the mid-season. The treatment of Admire applied twice had the lowest adult population. In the treatments of Admire applied in the mid-season, number of adults was high in the early season. After the mid-season, adult population was still above the economic threshold even the overall population was significantly lower than other treatments. Mycotrol, Naturalis-L, Knack and Applaud, when used alone, did reduce the adult population in the early season, but did not provide satisfactory control, and also there were no significant differences among them. After the mid-season, when Admire was applied, numbers of adults on the treated plants significantly reduced even the population was still greater than the economic threshold, indicating that the application of Admire might be too late. The number of nymphs and pupae was significantly different among the treatments over all sampling dates. Ten weekly applications of Mycotrol and Naturalis-L alone did reduced the whitefly population but did not reduce the whitefly immature population below the economic threshold. Although the whitefly population on the plants treated with Knack and Applaud alone was significantly lower than on untreated plants after 5 biweekly applications, they did not provide effective control of the nymphs either. Multiple applications of the 4 biorational insecticides, Mycotrol, Naturalis-L, Knack and Applaud in the early season followed by a mid-season application of imidacloprid, did significantly reduced the population of live whitefly nymphs and pupae on the plants, even in some treatments the number of nymphs and pupae was still above the economic threshold. All biorational insecticides tested in this experiment did not provide good control, especially in the late season that most plants treated with biorational insecticides were collapsed and died prematurely except for the plants treated with imidacloprid because whitefly population in the experimental field was much greater than other fields on the same farm during the entire season. However, Admire still was the most effective insecticide tested in this study, even its effectiveness lasts a maximum of 11 wk. Admire applied once at transplanting was effective against the whitefly before the mid-season, but did not give adequate whitefly control after the mid-season. Admire applied twice, at transplanting and in the mid-season, provided the best control of both whitefly adults and immatures even in some treatments whiteflies were slightly greater than the economic threshold. This could be explained that the healthy green plants attracted more adults from the nearby died or dying plants, or adults on these died and dying plants were forced to relocate their feeding sites to the greener and healthier plants.
Investigator's Name(s): Eric T. Natwick & Keith S. Mayberry.
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 Cabbage
Cabbage var. Primero was sown at UC Desert Research & Extension Center 16 September 1997. Six insecticide treatments and an untreated control were replicated four times in a randomized complete design experiment. Insecticide treatments were as follows: Admire 2F at 0.5 lb ai/acre injected 3 inches below the seed-line pre-plant, Capture 2 EC at 0.08 lb ai/acre plus Thiodan 3 EC 0.75 lb ai/acre, CGA215944 50 WP at 0.062 lb ai/acre, CGA215944 50 WP at 0.094 lb ai/acre, CGA215944 50 WP at 0.062 lb ai/acre plus Sylgard 309 at 4 fl oz/100 gal, and CGA215944 50 WP at 0.094 lb ai/acre plus Sylgard 309 at 4 fl oz/100 gal,. Foliar sprays were applied on 9, 15, 22 & 29 October, and 5 & 12 November, 1997. Silverleaf whitefly, Bemisia argentifolii, were sampled by counting adults via leaf turn and eggs and nymphs were counted on 2.54 cm2 of leaf surface from basal leaves on ten plants at random from each plot on, 1, 13, 21 & 27 October and 4, 11, 17 & 24 November, and 2 & 8 December, 1997. Mature marketable lettuce heads per 0.002 acres per plot were harvested and weighs were recorded in pounds.
The of adult silverleaf whitefly means for the untreated control were greater than insecticide treatments on sampling dates after October 13 and for the seasonal mean values, p # 0.05. The nymphal means for the Capture + Thiodan treatment were lower than the untreated control on all post-treatment sampling dates and for the seasonal mean. The nymphal means for the Admire treatment were lower than the untreated control on all post-treatment sampling dates, except 13 October, and for the seasonal mean. The nymphal means for the CGA215944 treatments were rarely different than the untreated control throughout the study. There were no differences among the treatments for numbers of cabbage heads or weight of cabbage heads.
Investigator's Name(s): Eric T. Natwick & Keith S. Mayberry.
Affiliation & Location: University of California Cooperative Extension, University of California Desert Research and Extension Center, 1050 E. Holton Road, Holtville, CA 92250.
Research & Implementation Area: Section C: Chemical Control, Biopesticides, Resistance Management, and Application Methods.
Dates Covered by the Report: March - June 1998
Silverleaf Whitefly Control In Spring Planted Cantaloupe Melons, 1998
A stand of Cantaloupe melons, var. Topmark, was established at UC Desert Research & Extension Center 19 March 1998. Seven insecticide treatments and an untreated control were replicated four times in a randomized complete design experiment. Insecticide treatments were as follows: CGA-293343 2 SC as a soil injection at 0.036 lb ai/acre followed by CGA-215944 50 WG as a foliar spray at 0.089 lb ai/acre, CGA-293343 2 SC as a soil injection at 0.043 lb ai/acre followed by CGA-293343 25 WG as a foliar spray at 0.089 lb ai/acre, Admire 2F as a soil injection at 0.25 lb ai/acre followed by Applaud 70 WP as a foliar spray at 0.25 lb ai/acre, Admire 2F as a soil injection at 0.25 lb ai/acre followed by Applaud 70 WP as a foliar spray at 0.037 lb ai/acre, Admire 2F as a soil injection at 0.25 lb ai/acre followed by Applaud 70 WP at 0.25 lb ai/acre plus Phaser 3 EC at 0.75 lb ai/acre as a foliar spray, Admire 2F as a soil injection at 0.25 lb ai/acre followed by Capture 2 EC at 0.08 lb ai/acre plus Thiodan 3 EC at 0.75 lb ai/acre as a foliar spray, and Admire 2F as a soil injection at 0.25 lb ai/acre. Foliar insecticide treatments were applied four times at one week intervals from 18 & 26 May, 2 & 16 June, 1998 with the exceptions of CGA-293343 25 WG as a foliar spray at 0.089 lb ai/acre and CGA-293343 25 WG as a foliar spray at 0.089 lb ai/acre which were only applied on 16 June. Silverleaf whitefly adults were counted on the fifth leaf from the terminal of the main stem cane from ten plants at random in each plot via the leaf turn method on 1, 3, 11, 15, 25 May, 1, 8, 24 and 30 June 1998. Silverleaf whitefly eggs and nymphs were counted on 2.54 cm leaf disks from ten crown leaves extracted from randomly selected melon plants in each plot on 4, 11, 18, 25 May, 1, 8, 24, and 30 June 1998.
There were no differences among treatments for adult counts on sampling dates from 1 May through 1 June. The non-treated control and the CGA-215944 treatments had more adults than Admire 2F followed by Applaud 70 WP + Phaser 3 EC and Admire 2F followed by Capture 2 EC + Thiodan 3 EC on 8 June (p# 0.05). The Admire 2F followed by Applaud 70 WP treatments had fewer whitefly adults than the control and CGA-293343 2SC followed by CGA-293343 25 WG. On 16 June, Admire 2F followed by Capture 2 EC + Thiodan 3 EC had fewer whitefly adults than all other treatments except Admire 2F as a soil injection at 0.025 lb ai/acre followed by Applaud 70 WP as a foliar spray at 0.037 lb ai/acre which had fewer adults than the control, the CGA-215944 treatments and Admire used alone. On 24 June, the control had more adults than all other treatments and Admire 2F followed by Capture 2 EC + Thiodan 3 EC had fewer whitefly adults than all other treatments except CGA-293343 2 SC as a soil injection at 0.043 lb ai/acre followed by CGA-293343 25 WG as a foliar spray at 0.089 lb ai/acre and Admire 2F as a soil injection at 0.25 lb ai/acre followed by Applaud 70 WP as a foliar spray at 0.25 lb ai/acre. On June 30, CGA-293343 2 SC as a soil injection at 0.036 lb ai/acre followed by CGA-215944 50 WG as a foliar spray at 0.089 lb ai/acre had fewer whitefly adults than all other treatments except the control, Admire alone and CGA-293343 2 SC as a soil injection at 0.043 lb ai/acre followed by CGA-293343 25 WG as a foliar spray at 0.089 lb ai/acre.
The control had more whitefly nymphs that the Admire treatments on 11 May through 25 May. The nymphal means for the CGA-215944 2 SC treatments were not different from the control until after the addition of foliar sprays on 16 June. Admire followed by Applaud at 0.37 lb ai/acre, Applaud plus Phaser or Capture Plus Thiodan provided the best control of whitefly nymphs through the season.
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