|CHU, CHANG CHI|
Submitted to: Sweetpotato Whitefly Progress Review Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 7/1/2000
Publication Date: N/A
Technical Abstract: In 1993 and 1994, we conducted studies to determine the effect of chemical control on silverleaf whitefly populations, upland cotton yield and honeydew contamination. Different population densities of silverleaf whiteflies were established with fenpropathrin-acephate insecticide mixture treatments during the growing season at the Irrigated Desert Research Station, Brawley, CA. Regression analyses showed that the highest cotton lint yields and lowest lint stickiness occurred when silverleaf whitefly densities were 0.3 and 1.3 nymphs/cm(2) of leaf disk, respectively or 4.1 and 7.5 adults per leaf-turn from 5th main stem node leaves from terminals, respectively. In 1995 and 1996, we verified the 4 adults per leaf-turn (the highest cotton lint yields) action threshold with 15 adults (the highest economic return) per leaf-turn and an untreated control. Results showed that initiating chemical control at 4 adults per leaf-turn produced higher lint yields and less lint stickiness compared to initiating chemica control at 15 adults per leaf-turn. Higher lint yields and lower lint stickiness occurred at both treatment levels compared to untreated cotton. Initiating treatments at 15 adults per leaf-turn required 2 to 3 applications and initiating control at 4 adults per leaf-turn required 5 to 6 applications during 1995 and 1996, respectively. Economic returns based on insecticide costs and lint yield were highest when cottons were treated at 4 adults per leaf-turn. Cotton lint stickiness was considered in the analyses and discounts for sticky cotton could significantly reduce net monetary returns.