COTTON WATER-STRESS, ARTHROPOD DYNAMICS, AND MANAGEMENT OF BEMISIA-TABACI (HOMOPTERA, ALEYRODIDAE)

The effects of plant water stress on beneficial and pest insects infes ting 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, Bem isia tabaci (Gennadius), were reduced 45-69% and 22-36% in plots irrig ated weekly compared with those irrigated biweekly in 1993 and 1994, r espectively. In 1993, DPL-50 had more whiteflies of all stages than Pi ma S-7, but crop termination dates had no effect on seasonal densities of whiteflies. In 1994, fenpropathrin and acephate insecticide applic ations provided greater control of whiteflies than buprofezin, an inse ct growth-regulating insecticide. Application thresholds of 1 adult wh itefly per leaf resulted in lower whitefly densities than thresholds o f 5 or 10 adults per leaf. In 1994, pink bollworm larvae, Pectinophora gossypiella (Saunders), were reduced in plots treated with fenpropath rin and acephate and in plots treated for B, tabaci at the threshold o f 1 adult per leaf. More Lygus hesperus Knight were found in plots irr igated weekly than biweekly in both years. Leaf water potentials (-bar s), measured at 3, 7, or 14 d after irrigation in 1993, indicated grea ter plant water stress in cotton irrigated biweekly at;and 14 d after irrigation than in that irrigated weekly at 7 d after irrigation seedc otton were greater at thresholds of 1 than at 5 or 10 adult whiteflies per leaf. Combining reduced plant water stress of weekly irrigation w ith fenpropathrin and acephate applied at a threshold of 1 adult white fly per leaf provided the best control of B, tabaci.