Action thresholds for the management of Bemisia tabaci (Homoptera : Aleyrodidae) in cotton

A 2-yr, multistate project was initiated in 1994 to determine action thresh olds for management of Bemisia tabaci (Gennadius) Biotype B (=B. argentifol ii Bellows & Perring) in cotton using chemical insecticides. Identical expe rimental designs and data collection protocols were used at sites in Brawle y, CA, Yuma and Maricopa, AZ, and Weslaco, TX. The prescriptive application of insecticides based on 4 candidate action threshold levels (2.5, 5, 10, or 20 adult B. tabaci per leaf) were compared with one another and an untre ated control. In general, there were few differences in whitefly population s among action thresholds of 2.5, 5, and 10 adults per leaf at sites in Ari zona and California. All insecticide treatments typically reduced populatio n densities below those in untreated control plots. Insecticide application s were generally ineffective in Weslaco, possibly due to reduced insecticid e susceptibility or the late onset of pest infestation, and there were few differences in population density among treatments. Yields were higher in s prayed treatments, but there was little difference among threshold levels. Yield differences were not detected among any treatments for Yuma and Wesla co in 1994 and for Maricopa in 1995. The levels of lint stickiness due to h oneydew deposition, as measured by thermodetector, were not consistent amon g sites and were not generally related to pest densities in the different t hreshold treatments. Levels of stickiness tended to be higher in 1994. Ther e were no treatment effects on other standard measures of lint quality. A s imple budgeting analysis assuming $43.24/ha per application for insecticide s and $1.59/kg for lint suggested that action thresholds of 5-10 adults per leaf provided the highest net return at most sites.