Community-wide Implementation of Samplin and Action Thresholds for Whiteflies in Cotton

Sampling and decision -making plans for managing sweetpotato whiteflies were implemented within 8,000 acres of cotton within the LaveenTolleson area of central Arizona. On the average, thresholds utilized for the first whitefly treatment were lower than those recommended, but subsequent treatments were made at about recommended thresholds. Introduction Successful management of the sweetpotato whitefly (Bemisia tabaci Genn. strain B = Bemisia argentifolii Bellows & Perring) is partially dependent on careful monitoring of whitefly populations and timely application of effective insecticides. Recommendations for sampling whiteflies and making control decisions are presented in the University of Arizona Cooperative Extension publication "Sampling Sweetpotato Whiteflies in Cotton" (Ellsworth et al. 1994). To demonstrate the use of these plans, we collaborated with 5 pest control advisers (PCAs) in implementing these plans on the cotton acreage of 14 cotton growers within the Laveen -Tolleson community. Methods University trained and supervised scouts sampled adult whitefly numbers in each of 190 fields (8,000 acres) weekly. Each field was sampled until one week after the first whitefly treatment was applied. In 30 fields, weekly sampling continued until August 18. From May 23 to August 18, a total of 1220 samples were taken. Sampling methods outlined in Ellsworth et al. (1994) were used with the exception that the total number of whiteflies on a leaf were counted rather than using the binomial method. About half of the samples were counts of whiteflies on 100 leaves (25 leaves in each of 4 quadrants) to determine the adequacy of the sampling models developed in describing the spatial distribution of adult whitefly populations while the other half were counts of whiteflies on 30 leaves per field (15 leaves in each of 2 quadrants) to establish the practicality of the sampling method (Diehl et al. 1995). PCAs were provided with reports on whitefly numbers in fields they were responsible for, usually on the same day as the samples were taken. It was recommended that fields be treated when they reached a mean density of 5 to 10 adult whiteflies per leaf. This program was voluntary, however, and the ultimate control decision belonged to the individual PCA and grower. At the end of the cotton season, the PCAs involved in this program provided us with summaries of each insecticide application made in each field. This information was coupled with sampling information to estimate the actual thresholds used.