A range of action thresholds for the control of silverleaf whitefly, Bemisia argentifolii Bellows & Perring [previously b-strain sweetpotato whitefly, Bemisia tabaci (Gennadius)] was evaluated in 2 field experiments, one at Weslaco, TX, with a low population density of B. argentifolii and one at Yuma, AZ, with a high population density. In Texas, action thresholds for whiteflies of 0.5, 1, and 2 large nymphs per 7.6 cm2of leaf area and of 1, 3, and 6 adults per leaf were tested. In Arizona, action thresholds of 3 and 10 adults per leaf were tested. All thresholds were compared with weekly insecticide treatments and an untreated control. The threshold treatment in Texas that resulted in the highest net return (70% increase over the untreated control) was 0.5 large nymphs per 7.6 cm2 of leaf area. The threshold treatment in Arizona that resulted in the highest net return (170% increase over the untreated control) was 3 adults per leaf. Both of these thresholds resulted in 6 applications of insecticide or ≈½ of that used in the calendar treatments.
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Riley et al. (1995) studied this question.