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Vegetable IPM Updates Archive
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Whitefly Management on Fall Produce (September 2, 2015)
Now that the produce season has begun, one of the first pests you’re likely to encounter is adult whiteflies. However, thus far, adult numbers have been surprising light on fall melons compared to previous years. Whitefly populations sampled in our untreated experimental plots during the last week in August at the Yuma Ag Center, show that adult numbers are the lowest we’ve observed in August since 2008 (see graph below). However, several melon fields in the Wellton/Roll were found to have very high numbers this past weekend. In each case, the fields with high adult numbers were either adjacent to or within a ½ mile of cotton that had not defoliated yet. Once the cotton is defoliated, whitefly movement generally declines. Nonetheless, you can bet whiteflies will eventually show up in one of your fields. It is important that PCAs pay particular attention to early whitefly control on their newly planted produce crops. Prolonged feeding by heavy numbers of adults on seedling lettuce/cole crop plants can cause stunted plant growth. If you observe honeydew on leaves in the absence of nymphs then there are way too many adults on the seedling plants. There are likely too many eggs being laid as well. PCAs have a few options for effective residual control of adults, but good knockdown can be achieved on lettuce and cole crops with combinations of 1) pyrethroids tank-mixed with Orthene, 2) Venom, Assail, Scorpion (neonicotinoids), 3) Exirel (diamide), and 4) the newly registered Sivanto (buteolide). All of these products will provide 3-7 days or adult knockdown. To assess adult control under heavy migrations, try monitoring young leaves for the presence of light-colored eggs (newly laid) using a hand lens. Absence of newly laid eggs can be an indication that adults are not actively feeding on leaves or are dying before they can lay eggs. Furthermore, allowing adults to remain unchecked on small plants generally results in the development of large nymph populations that can cause significant growth/yield reductions in all produce crops. It is strongly recommended that growers apply a soil insecticide on lettuce and cole crops throughout September, and if the weather remains warm into mid-October. Soil applied imidacloprid (0.38 lbs. AI/ac) (e.g., Alias 2F-24 oz; Wrangler 4F-12 oz; Admire Pro- 10.5 oz) can provide control through thinning stage. Verimark applied at 13.5 oz/ac can provide excellent control of nymphs when applied at planting similar to the neonicotinoids to lettuce and cole crops. Once plants get larger, products like Movento, Exirel, Venom, Scorpion, Assail, Knack and Courier/Vetica can provide effective control of nymphs. For more information on whitefly biology, management and insecticide alternatives see these reports:Whitefly Management in Fall Produce-2015 and Insect Management on Desert Vegetables and Melons: Whitefly.

Adult Whitefly

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For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.

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