• 1998 Demonstration Project of Arizona Irrigated Cotton Production

      Dittmar, Stefan H.; Ellsworth, Peter C.; Hartman, Philip MacD; Martin, Edward C.; McCloskey, William B.; Olsen, Mary W.; Roth, Robert L.; Silvertooth, Jeffrey C.; Tronstad, Russell E.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1999)
      The 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. Due to the cold spring and sand-blasting, only a stand of 30,900 plants/A could be established with 84% terminal damage. 72 acreinches of water were used with 41.3 acre-inches in postplant irrigations. Weed control could be achieved with one preplant application and three cultivations. Three sprays against Lygus and one spray against whiteflies were necessary after the thresholds were exceeded. A total of 4120 lb seedcotton per acre were 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.
    • The 1999 Arizona Cotton Advisory Program

      Brown, P.; Russell, B.; Silvertooth, Jeffrey C.; Ellsworth, Peter C.; Olsen, Mary W.; Husman, Stephen H.; Walser, R.; Clark, L.; Dunn, D.; Schneider, M.; et al. (College of Agriculture, University of Arizona (Tucson, AZ), 1999)
      Arizona Cooperative Extension generates and distributes weather-based Planting Date and Cotton Development Advisories for 19 cotton production areas (Aguila, Buckeye, Cochise Co., Coolidge, Eloy, , Laveen, Litchfield Pk., Marana, Maricopa, Mohave Valley, Paloma, Parker, Pinal Co., Queen Creek, Roll, Safford and Yuma Valley). Planting Date Advisories are distributed from legal first planting date until the end of April and provide updates on heat-unit-based planting windows, recent and forecasted weather conditions, heat unit accumulations, variety selection, soil temperatures, recommended plant population, and early insect management and control. Cotton Development Advisories are distributed from early May through early September and provide updates on crop development, insects, weather and agronomy. The Cotton Advisory Program will continue in 1999, and growers may obtain advisories by mail/fax from local extension offices or by computer from the AZMET Internet Web Page (http://ag.arizona.edu/azmet). Major program changes planned for 1999 include 1) use of historical AZMET weather data for local normals and 2) elimination of the computer bulletin board as a computer-based means of retrieving the advisories.
    • EUP Evaluation of a Novel Insecticide for Lygus Control

      Ellsworth, Peter C.; Deeter, Brian; Whitlow, Mike; Silvertooth, Jeff; The University of Arizona, Department of Entomology & Maricopa Agricultural Center; Rhône-Poulenc Company, Fresno, CA; Arizona Cotton Research & Protection Council (College of Agriculture, University of Arizona (Tucson, AZ), 1999)
      Lygus became the number one pest of cotton in 1998 with statewide losses of over $16 million in spite of individual costs to the grower of over $55/A for control. Selective technologies for whitefly and pink bollworm control reduce the number of broad spectrum sprays that incidentally control Lygus. Control of Lygus depends mainly on just two related chemical classes of insecticides, organophosphates and carbamates. Over reliance on such a limited diversity of chemical controls increases the risk of resistance. Further, FQPA threatens the future availability of many of our main stay chemical controls. The study reported here sought to investigate the commercial suitability of a new compound, Regent®, for the control of Lygus. This novel mode of action represents one of the few potential new tools under development for Lygus management. Under a federal Emergency Use Permit (EUP), Regent was tested against two standards of Lygus control (Orthene® and Vydate®) and an untreated check. In a test of unusually high Lygus densities, Regent provided excellent control of small (instars 1–3) and large (instars 4–5) Lygus nymphs and may provide marginally better control of adults than current standards. None of the tested agents provided quick control or knockdown of adults. Rather, adult levels were reduced over time, most likely as a result of prevention of the development of new adults via nymphal control. All three materials protected cotton producing yields significantly higher than the check. The Orthene treatment had the highest yield, though not significantly higher than the Regent treatment which was effectively sprayed one less time than the other compounds.
    • Evaluation of Chemical Controls of Lygus hesperus in Arizona

      Ellsworth, Peter C.; Silvertooth, Jeff; The University of Arizona, Department of Entomology & Maricopa Agricultural Center (College of Agriculture, University of Arizona (Tucson, AZ), 1999)
      When other means fail to avoid damaging levels of an insect pest population, chemical control becomes necessary. Chemical control is a variable farm input which should be optimized to reduce economic damage by the pest while maximizing profit and minimizing exposure to secondary pest outbreaks, pest resurgence, and risks of insecticide resistance. To best balance these needs, a grower or PCA needs the best information possible for selecting and timing chemical controls. This study examines the array of Lygus chemical control options currently available as well as experimental compounds that may or may not be available in the future. While identifying the best chemical controls is the major objective of this study, insights into proper timing and duration of control are also discussed. In short, there are few, yet effective, Lygus insecticides available to growers currently. However, with proper rates and timing, significant yield protection can be achieved with Orthene® or Vydate®. To a lesser extent, Thiodan® (endosulfan) was also effective against Lygus, though higher rates than used in this study may be necessary to achieve acceptable control. The use of mixtures did not enhance control of Lygus over our two standards (Orthene or Vydate). Newer compounds were also studied; however, Mirids (plant bugs) are not worldwide targets for development by the agrochemical industry. Thus, most new compounds are effective on some other primary pest (e.g., whiteflies, boll weevil, thrips, aphids), and control of Lygus is merely a potential collateral benefit. Of these, the chloronicotinyls (e.g., Provado®, Actara®) were not practically effective against Lygus hesperus, in spite of their existing or pending labelling. Their labels are based on demonstrated efficacy against a related species present in cotton outside of the West (Lygus lineolaris). One compound shows excellent promise as a Lygus control agent, Regent® (fipronil). Under development by Rhône- Poulenc, this insecticide provides as good or better protection against Lygus than our best materials. In a system demanding multiple applications to control chronic Lygus populations, Regent could be key to the development of a sustainable use strategy that does not over rely on any single chemical class. None of the insecticides tested significantly controlled adult Lygus, except after repeated use and time. Even then, this effect was likely the result of generational control of the nymphal stage which thus produced fewer adults over time. Nymphal control was excellent for Orthene, Vydate, and Regent. Yields were up to five times higher in the best treatments relative to the untreated control. Other effects were also documented for the best treatments which have additional positive impact on grower profitability: shorter plants (better defoliation), higher lint turnouts, less gin trash, and a lower seed index.
    • Monitoring Bemisia Susceptibility to Applaud (buprofezin) during the 1998 Cotton Season

      Ellsworth, Peter C.; Sieglaff, D. H.; Yazui, M.; Lublinkhof, J.; Silvertooth, Jeff; The University of Arizona, Department of Entomology & Maricopa Agricultural Center; Nihon Nohyaku, Ltd., Osaka, Japan; AgrEvo USA Co., Wilmington, DE (College of Agriculture, University of Arizona (Tucson, AZ), 1999)
      Starting in 1993, we developed a field-based protocol for bioassaying sweetpotato whiteflies (SWF) for susceptibility to buprofezin (Applaud®). Since then, we have monitored Arizona SWF populations (up to 5 regions) for susceptibility to Applaud in four out of the last six seasons. We observed no appreciable decrease in susceptibility. Instead, we have observed an increase in susceptibility of present day whiteflies when compared to populations bioassayed in 1993 and 1996, before any Applaud use in the U.S.. This result, however, is likely related to various procedural changes in the bioassay methodology. Nevertheless, our current estimates of whitefly susceptibility are similar to those obtained from various unexposed populations from around the world and to populations we bioassayed in 1997. Differences between our LC50 estimates and those of some other researchers can probably be explained by various procedural differences: 1) method of Applaud application, 2) whitefly stage collected and sources of leaf foliage, and 3) bioassay environmental conditions. Our results also showed each year that Applaud susceptibility does not decline after Applaud application(s) based on commercial paired field comparisons and replicated small and large plot evaluations. In fact, susceptibilities actually marginally increased after an Applaud application. This fact does not alter the recommendation for Arizona to limit Applaud use to one time per crop season, but does provide hope for the development of a sustainable use pattern even if usage continues on non-cotton hosts (i.e., on melons and vegetables under Section 18). Given the tremendous value of this mode of action, however, commodity groups should work together wherever possible to coordinate the usage of this and other valuable compounds so that whitefly generations are not successively exposed to this product.
    • Mortality Factors Affecting Whitefly Populations in Arizona Cotton Management Systems: Life Table Analysis

      Naranjo, Steven E.; Ellsworth, Peter C.; Silvertooth, Jeff; USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ and 2University of Arizona, Maricopa, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 1999)
      Direct-observation studies were conducted in replicated experimental plots to identify causes and estimate rates of mortality of whiteflies in cotton over the course of six generations from late June through late October. In plots receiving no whitefly or Lygus insecticides, predation and dislodgment were major sources of egg and nymphal mortality, and overall survival from egg to adult ranged from 0-18.2%. Similar patterns were observed in plots treated with the insect growth regulator (IGR) Knack. Applications of the IGR Applaud or a mixture of endosulfan and Ovasyn caused high levels of small nymph mortality and reduced rates of predation on nymphs during the generation immediately following single applications of these materials in early August. Whitefly populations declined to very low levels by mid-August in all plots, and few differences were observed in patterns of whitefly mortality among treated and control plots 4-6 weeks after application. The population crash was associated with an unknown nymphal mortality factor which reduced immature survivorship during this first posttreatment generation to zero. The application of insecticides for control of Lygus in subplots modified patterns of mortality in all whitefly treatments by generally reducing mortality from predation during generations observed from mid-July through August. Parasitism was a very minor source of mortality throughout and was unaffected by whitefly or Lygus insecticides.
    • Preliminary Evaluation of the "Next Generation" of Bt Cotton

      Sieglaff, D. H.; Ellsworth, Peter C.; Silvertooth, Jeffrey C.; Hamilton, E.; Silvertooth, Jeff; The University of Arizona, Department of Entomology & Maricopa Agricultural Center; Department of Plant Sciences; Monsanto Company, Chesterfield, MO (College of Agriculture, University of Arizona (Tucson, AZ), 1999)
      The next generation of Bollgard® cotton was evaluated for agronomic and insecticidal efficacy under central Arizona growing conditions. Two novel lines were compared with their recurrent parents, DP50 and DP50B. There were no seasonlong differences observed among the varieties in most plant development and insect parameters. However, DP50 had significantly lower emergence than the other lines tested (possibly related to seed quality). The lower plant population may have been responsible for greater whitefly abundance observed on two dates mid-season. During early-season ratings of secondary “pests” (15 DAP) (scaled on damage and/or presence), the two test lines received lower ratings for thrips and flea beetle when compared with DP50, DP50B and DP50Bu (untreated for Lepidoptera). However, these difference are likely as a result of the difference in seed treatments that the two test lines received (Gaucho®) and the others did not. This seed treatment does have known activity against thrips and beetle pests. In mid-season, the two test lines received lower ratings for beet armyworm when compared to DP50, DP50B and DP50Bu (although, not significantly different from DP50B or DP50Bu). Efficacy against pink bollworm (PBW) was assessed one time at the end of the season (we were limited to this time, so as to not affect yield), and DP50 was the only variety in which PBW exit holes were observed and PBW larvae collected. However, the low Lepidoptera pressure experienced during the season limited assessments of the two novel lines’ efficacy toward PBW. There was no significant difference in yield (bale/A) among the varieties. Although, one of the test lines had a lower lint turnout than each other variety. The two novel Bollgard lines performed well under our growing conditions, but continued evaluations will be necessary under more conditions and more insect pressures before “varietal” performance and gene efficacy can be assessed adequately.
    • Whitefly Management with Insect Growth Regulators and the influence of Lygus Controls

      Ellsworth, Peter C.; Naranjo, Steve E.; Silvertooth, Jeff; The University of Arizona, Department of Entomology & Maricopa Agricultural Center; USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 1999)
      The three keys to whitefly management are sampling, effective chemical use, and avoidance. This study examines factors relevant to the latter two keys in the context of Arizona’s cotton pest spectrum. Insect growth regulators (IGRs) are central to Arizona’s success in whitefly management. The basic usage guidelines developed for the IGRs—initial treatment timing, prescribed intervals between successive uses, and one use each seasonal limits—are all valuable in the development of a sustainable use pattern. Re-treatment timing guidelines for the second IGR has been the subject of investigation for the past two years. However, whitefly pressure in 1998 was strikingly different and lower than in any other post-introduction year. Re-treatment was unnecessary and thus could not be evaluated this year. Lygus, on the other hand, were at damaging levels early in plant development and for a protracted period. Future successes in whitefly management should consider the whole pest spectrum and depend on integrating chemical controls for all sprayed pests. While our primary focus is to optimize management of whiteflies in the context of other pests, this study examined the impact of Lygus controls on whitefly population dynamics and cotton production. Three sprays were required to control Lygus populations in this study. These sprays were atypically non-disruptive to whitefly population dynamics, and instead, helped to suppress low-level populations of whiteflies even further. This lack of disruption may have been due in part to the reduced abundance and role of natural enemies in this study. Lygus sprays did protect yields with a 3-fold advantage over untreated plots. Furthermore, there were a series of negative consequences of poor Lygus control. Plants tended to be more vegetative and more difficult to defoliate. Lower lint turnouts were documented for the Lygus-untreated areas. Sources of this additional loss were identified and included increased gin trash and larger seed size in Lygus-untreated areas. The lint also had significantly more sticking points as measured by manual thermodetector. While all cotton was determined to be non-sticky, this increased contamination may have been also related to the higher trash levels. Because of the differences in outcome in 1997 and 1998 in terms of Lygus spray effects on whiteflies, it is even more imperative that we further test whitefly management systems under near commercial conditions. A better understanding of the relationship between the control programs for these two major pests will help guide decisions on remedial inputs. This study also serves as an annual, replicated, and systematic accounting of whitefly population dynamics and control requirements useful for making historical comparisons across years. Inferences may be drawn about what are and are not the underlying causes of the unusual population dynamics observed in 1998.