Section F: Integrated and Areawide Pest Management Approaches, and Crop Management Systems - 1999
Authors: J. C. Palumbo, P. C. Ellsworth, T. J. Dennehy, and K. Umeda.
Affiliation & Location: University of Arizona, Yuma, Maricopa and Tucson, AZ.
A Grower Initiated Model for Sustaining Chemical Efficacy Across Commodities
During the past decade, the silverleaf whitefly in Arizona has been relegated to a managed pest. This was achieved primarily through the development of integrated pest management programs in cotton, melons and vegetables which promoted avoidance of whiteflies through cultural practices, use of selective insecticides, extensive sampling and monitoring protocols, and rational, prudent, and optimally-timed insecticide use. Growers in all commodities were quick to adopt and modify these management strategies as new insecticide compounds became available.
Emergency Exemptions (Section 18) for Admire® in melon and vegetables, and Danitol® in cotton, were first available to Arizona growers in 1993. However, due to excessive use, pyrethroid efficacy was significantly reduced in some growing areas by 1995. In response, the Arizona Cotton Growers Association (ACGA) requested limited use of and received an exemption for two insect growth regulators, Knack® and Applaud®. Availability of the IGRs made possible the UA Integrated Resistance Management program that promoted non-chemical management of whiteflies, in conjunction with a three-stage chemical use strategy designed to maximize the longevity of insecticide modes of action. Implementation of this program has since reduced insecticide use for whitefly management overall, and provided for recovery of pyrethroid efficacy.
Admire has provided consistent whitefly control on melons and leafy vegetables for the past six years. However, growers have recently become concerned about resistance risks associated with intensive Admire use on melons and the lack of registered insecticides with which to alternate. In 1998, the Western Growers Association (WGA) requested and received an exemption for the use of Applaud on melons in an attempt to diversify the chemistries available to control whitefly and sustain Admire efficacy. Because whitefly exposure to Applaud may soon overlap among melons, cotton and fall vegetable crops, cooperation will be needed among growers to harmonize insecticide use among commodities, to cover management needs of the respective groups, and to protect long-term Applaud efficacy.
Thus, in the spring of 1998, the leadership within the WGA and ACGA met to discuss the possibilities of developing a cross-commodity approach for managing whiteflies and sustaining long-term insecticide efficacy. A Cross-Commodity Growers Working Group was formed, and discussions focused on formulating practical pest management guidelines for cotton, melon and vegetable growers in Arizona. Participants also included representatives from the Arizona Vegetable Growers Association, Yuma Vegetable Shippers Association, Arizona Cotton Research and Protection Council, Cotton Incorporated, and Arizona Department of Agriculture. A technical working group was formed and comprised of University of Arizona research scientists and extension specialists, Arizona Department of Agriculture officials and pest control advisors from each commodity and regional growing area. This group was charged with developing insecticide use guidelines for the 1999 growing seasons, identifying potential vulnerabilities for the short-term (2-3 years), and developing long-term strategies for stabilization of chemical efficacy against whitefly and introduction of new pest management tactics.
The efforts of the technical working group have resulted in the development of a model approach to examining possible strategies for sustaining chemical efficacy in multiple cropping systems. The process involved compiling data for crop production, insecticide use patterns, and simulated whitefly population dynamics for key host crops within three distinct growing regions in Arizona, and constructing graphs that when overlaid identify important, multidimensional interactions within cropping systems. Based on the patterns resulting from our analysis, initial recommendations have been formulated to harmonize chemical use across commodities by restricting Applaud use to only once per crop season in specified use windows, with additional guidelines for reducing the possibility of exposing successive whitefly generations to the same mode of action. The diversification and limitation of alternative chemistries, such as Admire and Knack, and the refinement of cultural practices are to be considered as well. Should this model of cooperation be successful, valuable and scarce modes of action may also be shared in the future within diverse, integrated use systems.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 F: Integrated and Areawide Pest Management Approaches and Crop Management Systems.
Dates Covered by the Report: June 1997 - October 1998
Progress in Development of IPM for Upland Cotton in Arizona Using Biorational and Biopesticide Agents for Control of Silverleaf Whitefly (SLWF) Bemisia argentifolii and Other Cotton Pests
An Integrated Pest Management (IPM) program that used biorational/biopesticide agents as components was tested. We need IPM cotton programs with low impacts on natural or exotic populations of beneficial arthropods in classic or augmented systems. Such IPM programs need to control all pests, with biorational agents replacing conventional chemistries and incorporate Insecticide Resistance Management (IRM) to reduce likely development of insecticide resistance. Biorational/ biopesticides "fit" IRM since usually, they require different detoxification modes as they have widely different action modes. Deltapine upland cotton was planted and furrow irrigated. In 1997, we used DP 5415. Plots were 192.5 ft. in length and 6 rows across (40-in. rows) and plots were separated by 2 fallow rows and 8 ft. alleys. In 1998, we used NuCOTN 33B in plots 109 ft. in length and 12 rows across (40-in. rows) and plots were separated by 4 fallow rows and 20 ft. alleys. Ground applications were made. In 1997, applications were with 3 nozzles/row; 1 overhead, and 2 with swivel nozzles angled upward on drops; and applied at 80 psi and 30 gal./ac. In 1998, 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; and applied at 250 psi and 30 gal./ac. Biorational entomopathogens against SLWF included: Beauveria bassiana as Naturalis®L (Troy Biosciences Inc.) 10 oz. Product/ac, 2.3x 107 conidiia/ml; Beauveria bassiana as Mycotrol® (Mycotech Corp.), 0.5 lbs./ac, 2 x 10 13 spores/lb.; Paecilomyces fumosoroseus as PFR- 97® (Thermo Trilogy Corp.), 0.025 lbs. / gal., 1x 10 9 CFU (spores)/ gm equivalent 20% product. Biorational insect growth regulators against SLWF, at full rates as single or multiple applications, included: azadirachtin as BollwhipTM (other action modes also, Thermo Trilogy Corp.), 4.5% formulation, at 3,6,and 9 oz product /ac in 1997and 1 rate of 6 oz/ac product in 1998; buprofezin as ApplaudTM 70WP, AgrEvo, 0.35 lb. AI/ac; and pyriproxyfen as KnackTM 0.86,Valent USA), 0.54 lb. AI/ac. Applications were made once SLWF populations reached the action threshold (Univ. AZ recommendations). Biorationals used against insects other than silverleaf whitefly included: Pink bollworm sex pheromone, alone and baited with 1/10 rate chlorpyrifos; BT gene [NuCOTN 33B]; diflubenzoran [Dimilin®]; BT sprays[e.g. DiPel®];and K salt of fatty acid [M-PedeTM]. These treatments were used against pink bollworm, beet armyworm, cabbage looper, and saltmarsh caterpillar (per label). Treatments were part of a random block design that included a "Best Agricultural Practice regime" BAP, and a 1-ac block control. There were 16 treatments in 1997 and 12 in 1998. Weekly sweeps were taken in all plots for predators, parasites, and Lygus. In 1997, P. fumosoroseus, efficacies were as follows: 82.5% for eggs; 78.1 and 74.6% for small and large nymphs, respectively. These efficacies were similar to the BAP. B. bassiana, both products, gave excellent control of SLWF(>P. fumosoroseus) . The 1998 cotton season was a poor production year. SLWF populations reached action thresholds between July 27- Aug.6, 1998. Two sprays were applied in an 8-day period. Then, SLWF populations dropped sharply and did not rebound. Efficacies were as follows: against eggs; Beauveria bassiana, 41 and 23 % as Naturalis L® and Mycotrol®, respectively; and PFR-97, 30%; against small nymphs; Beauveria bassiana, 6 and 19 % as Naturalis L®and Mycotrol®, respectively; and PFR-97®; 24%; against large nymphs, Beauveria bassiana, 28 and 8% as Naturalis L® and Mycotrol®, respectively; and PFR-97® ,4 %. Despite these low efficacy rates, the SLWF populations remained below action thresholds. Buprofezin (ApplaudTM), the first and only BAP applied had egg, small nymphs, and large nymph efficacies of 28, 37, 38% respectively. This attempt need to control all pests, with biorational agents replacing conventional chemistries failed because of strong Lygus pressure that required one application of oxamyl, Vydate® in 1997 and several in 1998 (only1 applied). Presently, we have no biorationals for use against Lygus.
Affiliation & Location: USDA, ARS, Western Cotton Research Lab, Phoenix, AZ.
Research & Implementation Area: Section F: Integrated and Areawide Pest Management Approaches and Crop Management Systems.
Dates Covered by the Report: 1998 Cotton Field Season
Concentration and Management of Bemisia tabaci in Melons as a Trap Crop for Cotton
As a widely polyphagous herbivore, Bemisia tabaci utilizes an array of crop and non-crop hosts throughout its annual growth and decline cycle. Consistent differences in the relative abundances of B. tabaci on synchronously occurring hosts have strongly suggested behavioral and physiological differences in its acceptance of and performance on various hosts, respectively. Densities of B. tabaci recorded in both experimental and commercial field settings often have been highest in muskmelon (Cucumis melo) relative to cotton (Gossypium hirsutum) or other suitable host crops. Similar findings have been demonstrated under more controlled conditions in the laboratory or greenhouse. The potential application of such findings is that if the assortative host finding and acceptance behavior is strongly developed towards a particular host relative to others, then that host might be used to concentrate immigrating B. tabaci into strategically placed strips on the perimeter of and within the protected crop. Chemical control could then be concentrated just in the limited area of the trap crop while allowing natural enemies to operate unhindered by insecticides in the protected crop.
Besides possessing the necessary biological attributes for arrestment and retention of dispersing and foraging B. tabaci adults, a suitable trap crop must be agronomically and phenologically compatible with the principle crop. In the present study, melons were used as a trap crop with cotton as the principle crop. Both are heat tolerant, summertime crops that perform well under similar field preparation and irrigation regimes. A randomized complete block design was used at the University of Arizona Maricopa Agricultural Center to measure whitefly densities on cotton either protected by melons or unprotected without melons. Four replicate, sequential blocks were planted that consisted of 24 consecutive rows of protected cotton with 4 rows of melons planted on either side, a 12 row fallow area, and then another 24 rows of unprotected cotton with 4 rows on either side, but unplanted. A fallow area of 40 ft. separated each block. In the rows adjacent to the protected cotton, sequential plantings of melons were carried out so that robust melon plants would be present throughout the period of heaviest whitefly attack right up through the end of the cotton season. Melon plants in the 6-8 leaf stage were treated with a soil drench of imidacloprid followed by buprofezin+endosulfan and bifenthrin+endosulfan. No insecticides were applied to either the protected or unprotected cotton. The first planting of melons was disked in late July immediately following a knock-down application of endosulfan. A total of 48 leaf disks (2.5 cm2) were collected weekly from each replicate (192 per treatment ) over 12 consecutive weeks (6 July-23 September). Eggs, small and large nymphs, and pupal exuviae were counted on all disks and statistically analyzed on a week by week basis.
Egg and small nymph densities on melons were more than 10-fold greater than on cotton 9 of the 12 dates. A similar magnitude of difference between the two crops was observed for large nymphs and exuviae up to the time that buprofezin was applied to melons, after which the difference declined. Density differences between protected and unprotected cotton were less distinct due partly to strong block effects. For instance, block I had higher densities of whiteflies in both treatments than the other 3 blocks. As an end block adjacent to soybean and vegetable plots, whitefly immigration into block I appeared to occur at the ends of the treatment plots where no melons were planted. In contrast, the interior blocks II and III had higher densities in unprotected cotton relative to protected cotton over much of the season. Differences between treatments in end block IV were similarly less distinct as in block I.
Experimental evaluation of the potential benefits of trap crops in reducing densities of B. tabaci or other pests is problematical due to non-independent treatment effects. Greater isolation between trap-crop protected and non-protected principle crops is required to minimize the influence of one treatment upon another. A second field season will attempt to examine the same two treatments, but using non-contiguous blocks with greater distance between treatment plots. A full perimeter of melons will be grown around protected treatment plots rather than on two sides only as was done for the current report.
Affiliation & Location: 1USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ, 2University of California Imperial County Cooperative Research and Extension Center, Holtville, CA, and 3USDA-ARS Cotton Quality Research Station., Clemson, SC.
Research & Implementation Area: Section F: Integrated and Areawide Pest Management Approaches and Crop Management Systems.
Dates Covered by the Report: 1992 - 1997
Upland Cotton Susceptibility to Silverleaf Whitefly Infestations
Fifteen upland cotton, Gossypium hirsutum L., cultivars were evaluated in the field for susceptibility to silverleaf whitefly, Bemisia argentifolii Bellows and Perring, in Imperial Valley, CA from 1992 to 1996. The cultivars were Chembred 232, 333, 1135, 1233, Deltapine (DPL) 20, 50, 90, 5409, 5415, 5432, 5461, 5517, 5690, Louisiana (LA) 887, and Stoneville (ST) 474. All cultivars were susceptible to whitefly infestation. Sticky cotton occurred and lint yields were low in all cultivars. In 1995 and 1996, in each case, nine untreated and insecticide-treated cultivars were compared using 4.1 adults per leaf turn as an insecticide-treatment action threshold. Lint yields of the insecticide-treated plots were from 1.2 to 7.9 X in 1995 and from 0.35 to 4.0 X in 1996 when compared to lint yields of untreated plots. On the bases of the 4.1 adults per leaf cotton threshold, DPL 5409 and 5415 on average required 5.5 insecticide applications, DPL 50, 5461, and 5517 required six applications, and DPL 5432 and 5690 required 6.5 applications. LA 887 required seven applications and ST 474 required 7.5 applications. In a no-choice greenhouse trial in 1997, equal numbers of B. argentifolii eggs and nymphs were produced in small leaf cages for the nine cultivars and adult emergence was not significantly different between cultivars. Results suggest the potential to reduce insecticide applications by selecting appropriate cultivars currently available. Identification of resistance mechanisms and development of breeding programs to incorporate resistance into acceptable upland cultivars appears to be a promising approach for whitefly control.
Affiliation & Location: 1USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ, and 2University of California Imperial County Research and Extension Center, Holtville, CA.
Dates Covered by the Report: 1983 - 1995
Effects of Aldicarb on Cotton Insects and Plant Growth and Yield
Soil application of aldicarb reduced numbers of sweetpotato whitefly, Bemisia tabaci Gennadius, in studies conducted in 1983 and 1984, but not silverleaf whitefly, B. argentifolii Bellows and Perring, in studies conducted from 1988 and 1990, on upland cotton, Gossypium hirsutum L. Aldicarb-treated plants also had significantly fewer thrips, Frankliniella spp., leafhoppers, Empoasca spp., and damsel bugs, Nabis spp. early in the season, than untreated plants. Aldicarb-treated plants exhibited more vigorous plant growth than untreated plants. In mid- to late season from 21 June to 26 July in 1993 when the silverleaf whitefly population density was low (8.0 nymphs/cm2 leaf disk for untreated plants) fewer silverleaf whitefly occurred on aldicarb-treated plants (4.4 nymphs/cm2 leaf disk). Lint yield increase was 42% as compared to untreated plants. In 1994, when silverleaf whitefly population density was high (18.9 nymphs/cm2 leaf disk for untreated plants) during mid- to late season (from 15 June to 27 July), aldicarb was not effective.
Affiliation & Location: 1USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ, 2University of California Imperial County Research and Extension Center, Holtville, CA, and 3USEPA Ecology Effect Branch, Washington,
Dates Covered by the Report: 1991 - 1995
Effects of Pyrethroid Insecticides Alone and in Mixtures on Silverleaf Whitefly and Cotton, Cauliflower, and Broccoli Yields
Insecticide efficacy studies for silverleaf whitefly, Bemisia argentifolii Bellows and Perring, control were conducted in the Imperial Valley, California from 1991 to 1995. Three studies were conducted on cotton in 1992, 1994 and 1995, one on broccoli in 1991 and one on cauliflower in 1993. Results showed that silverleaf whitefly control on cotton, broccoli and cauliflower was more effective when a pyrethroid insecticide (e.g. fenpropathrin or bifenthrin) was mixed with an organophosphate (e.g. acephate) or a cyclodiene (e.g. tralomethrin) compound as compared to either material used alone. The effect appeared to be additive toxicity of pyrethroid and a second compound with a different mode of action. Cotton lint and cauliflower yields were increased and broccoli matured earlier in pyrethroid-phosphate or pyrethroid-cyclodiene mixture treated plots as compared to plots treated with the individual chemicals alone.
Affiliation & Location: The University of Arizona, Cooperative Extension, Maricopa & Tucson, AZ.
Dates Covered by the Report: 1998
Interdisciplinary Demonstration of Arizona Irrigated Cotton Production
A demonstration project was conducted on the Demonstration Farm at the Maricopa Agricultural Center. In this project all current guidelines and recommendations disseminated by The University of Arizona were integrated in a systems approach. The management decisions were made by the Extension Specialists in agronomy, entomology, irrigation management, weed sciences, and plant pathology following the University recommendations. On a 50.5 acre field 80% Bt and 20% non-Bt cotton was planted dry and watered up. Dueto the cold spring and sand-blasting, only a stand of 30,900 plants/A could be established with 84% terminal damage. A total of 72 acre-inches of water were used with 41.3 acre-inches in post plant irrigations. Weed control was achieved with one preplant application and three cultivations. Whitefly management was fully integrated with management of other insect pests. Sampling and threshold guidelines were followed for each pest. Three sprays against Lygus and one spray against whiteflies were necessary after the thresholds were exceeded. Knack¨ (pyriproxyfen) was selected for control of whiteflies based on published guidelines. No further applications were necessary for whiteflies. Our demonstration, which was located in the center of over 200,000 A of cotton in central Arizona, produced sticky-free cotton with higher than average yields and with pest management under budget. In 1998, the average number of sprays made statewide for all insects was 4.7; our demonstration required only 4. The average number of sprays required for whitefly control statewide was 1.05; our demonstration required just 1 spray. Lygus were the most chronic and yield-limiting insect in this study. Nevertheless, yields were higher than the statewide average of 1100 lbs/A, higher than the historical farm-wide average (ca. 1340 lbs/A), and higher than the farm-wide average for 1998. A total of 4120 lb seed cotton per acre was harvested, with 32.7% lint turnout (2.81 bales/A)and 45.9% seed turnout (1891 lb/A). After harvesting a field budget was established. The variable costs per acre were $915, the total cost $1266/acre. In spite of the lack of replications this project validates the usefulness and compatibility of University recommendations and the potential for integration of all disciplinary guidelines in one system.
Affiliation & Location: The University of Arizona, Department of Entomology & Maricopa Agricultural Center, Maricopa, AZ.
Dates Covered by the Report: 1995 - 1998
Whitefly Management in Cotton - A Historical Perspective
It has been less than 6 years since the devastation of the whitefly in Arizona and southern California. Numbers were so dense that windshields were clouded with the bodies of the adults, unprotected cotton fields were "biologically" defoliated, and fields stood in "permanent" wilt due to the excessive stress imposed by the immatures. Today our program has evolved from an effective, yet 2-dimensional system of chemical management to a multi-faceted, 3-dimensional and integrated management strategy. Early on the three "keys" to whitefly management were identified by us and others as 1) Sampling and detection, 2) Effective chemical use, and 3) Avoidance of the problem. Now, this matrix of factors can be represented in the form of a pyramid, an inherently stable structure. "Avoidance" is the foundation block upon which "Effective Chemical Use" and "Sampling" rest. Confronted with a pest crisis, short term survival depends on the upper two levels of the pyramid. However, sustainable, long-term strategies ultimately must depend on the development of a solid foundation, "avoidance." At the same time, a pyramid-strategy developed for one pest must be compatible with like strategies in place for all pests of a system.
The building blocks of a successful pest management program can be further subdivided into component parts. Sampling in cotton involves multi-stage and binomial methods of classifying whitefly populations. These tools have been adapted for new chemistry as it was developed. Effective chemical use consists principally of the use of action thresholds, availability and understanding of selective and effective chemistry, and a proactive resistance management plan. Action thresholds have been developed that are effective at preventing yield and quality losses. These, too, are insect stage-specific and have been optimized for proper deployment of insect growth regulators (IGRs). The IGRs, Knack¨ and Applaud¨ ,became available for the first time in this country in 1996 and have had a sensational impact on the selective management of this pest. [However, one cannot understate the importance of concomitant use of Admire¨ (imidacloprid) in melons and vegetables to the overall, area-wide lowering of pest dynamics.]All chemistry has been organized into a 3-stage program of deployment for resistance management. The proactive nature of this program has led to the restriction of use of the new IGRs such that their modes of action may be preserved for as long as possible while providing relief for resistance risk to all products.
Adoption of IGRs and their proper use has been exceptional with over half to two thirds of all cotton acres being treated annually since 1996. The challenge remains, however, to further delve into the foundation block of our management program, avoidance. This level of management may be subdivided into three interrelated tiers of development, Cross-Commodity Cooperation, Exploitation of Pest Biology, and Crop Management. Key elements within these tiers are either in partial operation or development at this time. Dramatic successes so far 6.6 sprays against whiteflies in 1995 down to just over 1 spray in 1998 overshadow efforts to continue development of tactics of avoidance. Complacency in growers and the scientific community is a very real challenge to us now. Work should continue in all areas of avoidance; however, an opportunity has become available to make significant progress in cross-commodity cooperation with specific impacts on crop placement, alternate host management (source reduction),and inter-crop movement. As we build and strengthen our pyramid of whitefly management in cotton, we need to build similar structures of whitefly management for the other major crop hosts in Arizona(e.g., melons and vegetables). Only then can we fully realize an integrated, systemic, and sustainable solution to this highly mobile pest. Palumbo et al. (this volume) reported on just such an effort to rationalize chemical use and whitefly management among the major crop host commodities in Arizona. Their initial efforts will be to interlock resistance management programs among four host crops, spring melons, cotton, fall melons, and vegetables. The challenge remains to preserve our successes while redoubling efforts to develop and integrate more tactics of avoidance.
Affiliation & Location: 1 Plant Protection Unit, CATIE. Turrialba, Costa Rica, and 2Southwest Florida Research & Education Center (SWFREC), University of Florida, Immokalee, Florida.
Dates Covered by the Report: August 1997 - December 1998
Effectiveness of Living Ground Covers for Managing Spread of Geminiviruses in Tomato by Bemisia tabaci in Costa Rica
Staked tomatoes in Costa Rica are grown mainly on small plots (<0.5 ha) and often severely affected by the Tomato Yellow Mottle Virus (ToYMoV), vectored by Bemisia tabaci biotype C. The impact of the disease on crop yield depends on plant age at time of infection, and is greatest during the first eight weeks after germination. Therefore, management should focus on minimizing contact between the vector and the tomato plant during this period. Consequently, a two-phase preventative management scheme has been proposed: (1) protection of seedbeds with fine netting (Tildenet IN50, Tildenet Ltd., Arkansas) to produce high-quality, virus-free seedlings, and (2) masking the crop after transplanting from immigrating viruliferous whiteflies with living ground covers. This second phase is presently under investigation. Living ground covers are locally available, economical to establish and could provide resource-poor tomato growers with extra income through sale of seed, forage, or other products, organic matter to enrich the soil, and refugia for beneficial insects.
Three field experiments were recently conducted, one in Turrialba (Caribbean watershed) and two in Grecia (Pacific watershed), Costa Rica. Each experiment was actually a replicate of a single experiment to be replicated four times. A total of about 2400 m2 in each location was divided into six, 400 m2 plots randomly assigned to six ground cover treatments: Arachis pintoi (perennial peanuts) (Leguminosae), "cinquillo" (Drymaria cordata, Caryophyllaceae), coriander (Coriandrum sativum, Umbelliferae), silver plastic, bare ground treated with imidacloprid (commercial standard), and bare ground untreated (absolute control). Living covers were established well before tomatoes were transplanted. Silver plastic (silver/black, coextruded, 56" x 1.25 Mls; Olefinas S.A., Guatemala) was put in place over the 30 cm-wide bed two weeks before transplanting. Imidacloprid (Confidor 70 WG; Bayer) was applied to the foliage at the recommended rate (9 g/ 40 m2 of seedbed surface) a week before transplanting, and two drench applications (250 g/ha) two and four weeks later. No other insecticides were used in any plot during the rest of the season.
So far, silver plastic has been the best treatment in terms of reduction of incoming whitefly adults, delay of ToYMoV dissemination, reduction of disease severity, and highest tomato yields. It was followed by living covers, but their degree of effectiveness varied with each experiment. For Guayabo, area under the disease progress curve (AUDPC) was calculated for disease incidence at 2594 (silver plastic), 2027-2864 (living covers), imidacloprid (3290), and 4149 (bare soil), and for disease severity at 951, 791-1087, 1611, and 2402, respectively. Yields were 46, 25-40, 25 and 5 t/ha, respectively. For Grecia (I), corresponding AUDPC values were 511, 553-2845, 2002, and 5197 for disease incidence, and 260, 294-1624, 1170 and 3378 for disease severity. Yields were 28, 12-16, 11 and 10 t/ha, respectively. Vector pressure was highest during the second experiment at Grecia where the experimental plot was very close to a 2.5-ha commercial field heavily infected by the ToYMoV. There values for both disease incidence and severity were large for all treatments (1323-3899 and 512-2651, respectively) and yields were poor (1-13 t/ha).
Thus, both living and inert covers provided effective control of whitefly colonization and ToYMoV spread under moderate whitefly pressure, but control broke down under extremely high pressure. This result underlies the need to supplement both preventative and curative management tactics applied by the individual grower with area-wide preventative approaches, such as planting dates and crop-free periods, in order to successfully manage whitefly-vectored geminiviruses in Costa Rica.
Affiliation & Location: University of Arizona, Cooperative Extension, Maricopa County, Phoenix, Arizona.
Dates Covered by the Report: June 1995 - October 1998
Summary of Standardized Survey of Whitefly in the Gila Basin Near Gila Bend, AZ
A standard survey for whitefly adults was initiated in June 1995 as part of a grower initiated Integrated Pest Management Project. Field survey protocol used was the method developed by the University of Arizona. In 1995, data collected included adult whitefly density, planting date, variety and applications of insecticides. In 1996, whitefly nymphs were included in the survey. In 1997, the area surveyed included all of the fields in the Gila Basin. In 1998, forty fields of uniform age were select representing all areas of the basin. Each field was sampled once per week for 18 weeks.
Whitefly adults during 1995 were treated beginning in early July and continued for the remainder of the cotton-growing season. Fields averaged 5.2 treatments with combinations of up to five insecticides with little or no whitefly control achieved. On the average field were infested (>40% based on binomial leaf turn method) for an average of 5.1 weeks. In 1996 insect growth regulators, pyriproxyfen and buprofezin and genetically engineered cotton, with the `Bt' gene, was introduced into the basin. Field applications of insecticide for whitefly dropped dramatically to 1.9 treatments and averaged only 1.3 weeks above the 40% threshold for adults only. When both adults and nymphs were used as recommended the period above the threshold was only 1.0 weeks. In 1997, the average number of treatments per field held constant at 1.9 per field. The number of weeks adults were above the 40% threshold was 1.4 weeks but the nymphs were above the threshold for 3.7 weeks. In 1998 the fields averaged 1.8 treatments for whitefly per field. The number of weeks that the fields were above threshold increased to 2.4 for adults and 4.4 for nymphs. In general, the introduction of the insect growth regulators and the genetically altered cotton has resulted in lower whitefly populations.
Seasonal variation in weather conditions may also play a role in the timing and occurrence of whitefly population outbreaks.
Affiliation & Location: ARS, Central Arid Zone Research Institute, Jodhpur-342003, INDIA.
Dates Covered by the Report: June 1984 - October 1997
Integrated Management of Bemisia tabaci Genn (Aleyrodidae) and Yellow Moaisic Virus in Mothbean (Vigna aconitifoia ) Crop
The whitefly, Bemisia tabaci Gen. is a serious pest on leguminous crops in tropical and subtropical countries. Losses due to whitefly and YMV in pulse crops are estimated from 25 to 73% in different cultivars of Vigna spp. During favourable high temperatures of arid zone in India, the rate of whitefly reproduction is also high and the position of adults and immature stages on the underside of leaves has made this pest difficult to control. Increasing use of synthetic pesticides leads to serious problems like environmental pollution and insect resistance to insecticides. Therefore methods involving various agronomical practices, screening for pest resistance and use of plant products like neem extract, neem oil and neem seed powder were studied and an integrated approach for management of whitefly and YMV is suggested so that the use of pesticides is minimized.
The whitefly usually started attacking the crop from 3 rd week of August and the incidence of peak period of activity was 6.3-8.3/plant/catch. This insect becomes more serious pest as it also acts vector of yellow mosaic virus. Since the chlorophyll pigments of the leaves are destroyed, the photosynthesis is severely hampered and thus results in low productivity of crop. This results a loss of 15 to 50% loss in yield under different climatic conditions. In general, the loss in grain yield was minimum for the crop sown in first or second week of July.
Field screening of promising fifty-one cultivars of mothbean was carried out against Bemisia tabaci and YMV. Twenty-two cultivars so selected were subjected to series of stress trials. Seven cultivars viz. IPCMO-943, IPCMO-1035, T-16, T-2, Jadia, PLMO-240 and PLMO-216 were isolated to be the least susceptible to the pest and YMV.
Field trials conducted with neem products in providing pest protection umbrella to pulse crops highlights the need
for better understanding for the use of these ecofriendly products which are efficient antifeedant and repellent to pest attack.
The results on whitefly population varied significantly in different treatments. Use of monocrotophos was superior to
all treatments followed by neem oil, neem seed extract (5%), neem seed kernel extract (2%) and neem seed extract (2%).
The use of neem oil performed better than the aqueous extracts in reducing the population of whitefly.
Subsequently, there was significant reduction in YMV infection in mothbean crop. Increase of 20-55% grain yield was recorded
under arid zone cultivation of mothbean. The study thus revealed that these plant products may be suitably incorporated in
the IPM programme of mothbean. These extracts are cost effective as all the raw material is locally available which
can easily be exploited by the farmers for its use against whitefly and YMV.