Effects of the Plant Growth Regulator Mepiquat Chloride on Silverleaf Whitefly (Homoptera: Aleyrodidae) Infestations on Cotton²

Cotton, Gossypium hirsutum L., plants were treated with the plant growth regulator mepiquat chloride (Pix^™) in greenhouse and field plot tests to determine its effect on infestations of the silverleaf whitefly, Bemisia argentifolii Bellows and Perring. In the greenhouse, Pix-treated plants were significantly shorter and had thicker leaves than untreated plants by the end of the second week following application. Most of the Pix treatments caused significant reductions in adults, eggs and nymphs on leaves by fourth and final week of the test. In a separate test, leaf water potentials were equal for Pix-treated and well-watered plants which were significantly lower than for water-stressed and control plants. Pix-treated plants in two field plot tests showed the same changes in plant morphology observed in Pix-treated plants in the greenhouse. However, leaf water potentials were the same as in untreated plants and no reductions in whitefly infestations were found during the 6 to 7 wk test periods. Pix-treated plants in a third field plot test showed no changes in plant morphology or in whitefly infestations. The reduced whitefly infestations of Pix-treated plants in the greenhouse, but not in field plots, may have been due to reduced leaf water potentials in Pix-treated greenhouse plants but not in field plants.