Cotton water stress, arthropod dynamics, and management of Bemisia tabaci (Homoptera: Aleyrodidae)

The effects of plant water stress on beneficial and pest insects infesting Deltapine-50 short-staple cotton, Gossypium hirsutum L., and Pima S-7 long-staple cotton, Gossypium barbadense L., were studied in 1993 and 1994 in large replicated field plots in central Arizona. Seasonal densities of eggs, nymphs, or adults of the sweetpotato whitefly, Bemisia tabaci (Gennadius), were reduced 45-69% and 22-36% in plots irrigated weekly compared with those irrigated biweekly in 1993 and 1994, respectively. In 1993, DPL-50 had more whiteflies of all stages than Pima S-7, but crop termination dates had no effect on seasonal densities of whiteflies. In 1994, fenpropathrin and acephate insecticide applications provided greater control of whiteflies than buprofezin, an insect growth-regulating insecticide. Application thresholds of 1 adult whitefly per leaf resulted in lower whitefly densities than thresholds of 5 or 10 adults per leaf. In 1994, pink bollworm larvae, Pectinophora gossypiella (Saunders), were reduced in plots treated with fenpropathrin and acephate and in plots treated for B, tabaci at the threshold of 1 adult per leaf. More Lygus hesperus Knight were found in plots irrigated weekly than biweekly in both years. Leaf water potentials (-bars), measured at 3, 7, or 14 d after irrigation in 1993, indicated greater plant water stress in cotton irrigated biweekly at;and 14 d after irrigation than in that irrigated weekly at 7 d after irrigation seedcotton were greater at thresholds of 1 than at 5 or 10 adult whiteflies per leaf. Combining reduced plant water stress of weekly irrigation with fenpropathrin and acephate applied at a threshold of 1 adult whitefly per leaf provided the best control of B, tabaci.