Action Thresholds for Whiteflies in Arizona

Peter C. Ellsworth, Donna L. Meade


Three field tests were set-up for evaluation of action threshold levels for sweetpotato whitefly control with two different chemical combinations. The thresholds used to initiate treatments were ca. 1, 10, and 25 adult whiteflies per leaf. The insecticides used included a pyrethroid combination (Danitol®+Orthene®) and a non-pyrethroid combination (endosulfan+Ovasyn®). Populations were monitored as whitefly adults (leaf turns & net sweeps) and nymphs and eggs (leaf counts). Once applications were triggered, they continued ca. weekly. The early threshold required seven applications and produced yields which were 2 or 3 times larger than the untreated check. Lint or leaf stickiness was not apparent; however, 2 or 3 sprays were required before any significant differences in whitefly populations could be found. Whitefly numbers were lowered significantly in both insecticide regimens, with somewhat lower numbers present in the pyrethroid treated plots. The late threshold was sprayed only twice and yielded no more cotton than the untreated check. Lint and leaf surfaces were covered in stickiness and sooty mold. Whitefly populations were excessive and led to premature cut-out and poor fruit retention. The moderate threshold (10 adults per leaf) received five applications and produced high yielding and high quality cotton. Some stickiness and sooty mold growth was observable only on the lowest leaves. This was a result of limited honeydew production prior to the threshold and well before any boll opening. Lygus populations were extremely high and caused large differences in yields according to the two insecticide regimes. Given commercial farm control realities, the ideal threshold for initiation of treatments is likely between 1 and 10 adults per leaf. Further work is planned to refine these action threshold levels with sampling feedback in Az cotton.

Reprinted from Proceedings of the 1994 Beltwide Cotton Conferences pp. 878 - 881
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998