A whitefly resistance crisis in Arizona in 1995 prompted the development of a resistance management strategy in 1996 that recommended maximal once per season use of two insect growth regulators, pyriproxyfen (Knack®) and buprofezin (Applaud®), and limited and delayed use of synergized pyrethroid insecticides in cotton. Statewide monitoring of whitefly resistance has shown that implementation of this strategy has substantially reduced whitefly resistance to the synergized pyrethroids and has also resulted in increased susceptibility to key non pyrethroid insecticides. Having benefited from two years of success with this strategy, the Arizona cotton industry now faces the question of whether it can be sustained as pyriproxyfen and buprofezin gain additional registrations for use against whiteflies in vegetables, melons and glasshouse crops.

A resistance management program was initiated in Arizona in 1995, the initial goal of which was to sustain the efficacy of imidacloprid (Admire®) against Bemisia in vegetable crops. Due to the anticipated registration of additional chloronicotinyl (and related neonicotinyl) insecticides in Arizona, project objectives were subsequently broadened to address management of this entire class of insecticides in Arizona field crops. Results from three years of statewide monitoring of whiteflies from cotton indicated that whitefly populations in Arizona have become significantly less susceptible to imidacloprid in each of the past two years and significant geographical differences were described. However, no evidence was found of reduced field performance of imidacloprid in vegetables. Additionally, laboratory studies subjecting Arizona whiteflies to selection with imidacloprid did not increase levels of resistance beyond those occurring in the field. A study exploring the influence of cropping system differences on imidacloprid use (Admire® and Provado®) revealed no major differences in susceptibility to this insecticide between populations of whiteflies in central and southwestern Arizona. However, distinct seasonal shifts to lower susceptibility from 1996 to 1997 were observed in the Dome Valley of southwestern Arizona. Susceptibility of Arizona whitefly populations to imidacloprid was highly correlated with susceptibility to acetamiprid but was unrelated to susceptibility to CGA-293343. There is an urgent need to harmonize chemical use and resistance management efforts in Arizona cotton, vegetables and melons to avoid conflicts resulting from movement of pests between crops.

Integrated Lygus management depends on the same fundamentals of management for any pest. There needs to be a system of monitoring (sampling), understanding of the density-yield relationship (thresholds) and other insecticide optimization practices (e.g., resistance management), and a plan for reducing the chance of infestation and need for remedial measures (avoidance). While all these guidelines are under current study, current recommendations represent a fundamental base on which to build an integrated Lygus management program that will also manage for susceptibility to our current insecticides. Key to this sustainable susceptibility system is limiting insecticide use to the lowest practical levels. This is best accomplished by careful sampling, careful assessment of thresholds and selection of the right compound for the job, but, most of all, avoidance of the problem from the start. Current recommendations are detailed below in light of the most recent research findings.

Green bolls (100/field) were sampled from the uppermost internodes within adjacent fields of Bt (Deltapine 33B) and non-Bt (Hyperformer HS 44) cotton experiencing severe pink bollworm pressure late in the growing season. Average top crop lint yield reductions ranging from 30 to 70% were observed in the uppermost bolls of the non-Bt cotton variety. Average top crop lint yield reductions ranging from 0 to 40% were observed in the uppermost bolls of the transgenic Bt cotton variety.

Growers, Pest Control Advisors (PCA), and University of Arizona Cooperative Extension personnel formulated and coordinated area-wide pest management strategies in the production area near Gila Bend, Az. from 1995-97. The primary pest target was whitefly with secondary control strategy implementation for pink bollworm in 1995. In 1995-1996, the coordinated effort encompassed approximately 10,000 and 6000 acres which included 10 and 8 cotton producers respectively and 6 pest control advisors. Due to producer interest and initiative in an adjoining production area, project acreage increased to over 18,000 acres and included 14 producers and 9 pest control advisors in 1997. The project cost of $3.00/acre was supported by participating producers with the monies used to hire University of Arizona trained students for field scouting of whiteflies. An economic development grant from the Electrical District #8 supported the project coordinator's salary who is a University of Arizona employee. Each field was sampled weekly for whitefly populations using recommended University of Arizona sampling procedure. The population data was then faxed to the responsible producer and pest control advisor on the date of sample. Treatment thresholds and chemistry class suggestions were made by Cooperative Extension with final control decisions and material choice at the producer and pest control advisor discretion. Weekly community wide meetings were conducted and used to discuss general area-wide and field specific population dynamics, treatment suggestions, crop condition, and agronomic and entomological area -wide production strategy recommendations.

Neither Tracer nor Proclaim appeared to be effective pink bollworm materials whether applied at day or night. However against cotton leafperforator, both Tracer and Proclaim provided sufficient control. Although all three formulations of Karate equally provided statistically significant pink bollworm control, it was not commercially acceptable. Shortening the spray interval from 7 to 4 days may have helped alleviate this problem. None of the Karate formulations evaluated appeared to offer outstanding cotton leafperforator control.

Cotton pesticide application histories in the Gila Basin were followed from 27 April through 20 September. The main interest was the effect of early season applications to control pink bollworm, Pectinophora gossypiella, and other pests on subsequent whitefly applications. Categories explored include, transgenic and non transgenic cotton, planting dates, and location within the valley. Regression analysis shows a significant effect due to the early season control for either P. gossypiella, or other pests (P > 0.009) but lower for them together (P > 0.026). Early applications for either PBW or other pest resulted in increased application for whitefly.

Steinernema riobravis Cabanillas, Poinar & Raulston infected pink bollworm Pectinophora gossypiella (Saunders), larvae over a temperature range of 15.6 - 38.0° C. Temperatures of 32.2° C and higher and exposure for 48 h or more often resulted in decreased numbers of nematode killed larvae with living nematodes and increased numbers of dead larvae with dead or no nematodes.

All of nine cotton cultivars tested were susceptible to silverleaf whitey, Bemisia argentifolii Bellows and Perring in Imperial valley, CA in 1995 and 1996. Using 4.1 adults per leaf turn as an insecticide- treatment action threshold, Deltapine (DPL) 5409 and 5415 required 5.5 applications of insecticide, DPL 50, 5461, and 5517 required 6 applications, DPL 5432 and 5690 required 65 applications, Louisiana (LA) 887 required 7 application, and Stoneville (ST) 474 required 7.5 applications. Results indicate the potential to reduce insecticide application by selecting appropriate cultivars that are commercially available.

Experimental insecticides were evaluated for control of sweet potato whiteflies relative to a commercial standard in cotton. Ni-25 provided excellent whitefly control and was equivalent to the commercial standard (Knack followed by Danitol + Orthene). Fenoxycarb + pymetrozine provided goodwhitefly control but seemed to require 2 sequential applications before control was equivalent to Ni-25. Diofenolan + pymetrozine appeared to be a slightly weaker treatment, but still provided acceptable whitefly control.