Whitefly Management on Fall Produce (September 3, 2014)

Now that produce planting/transplanting is well underway, one of the first pests you’re likely to encounter is adult whiteflies. Given the high numbers found on spring melons and cotton this summer, one would also expect whiteflies to be heavy on fall produce crops. Surprisingly though, adult numbers have been lighter than expected on fall melons. For instance here at the Yuma Ag Center, whitefly populations in our experimental plots based on vacuum samples taken this week are lower than what we’ve encountered the past few years (see graph below). However, this appears to be site-specific as I’ve observed melon fields in the Wellton/Roll area with very high numbers this past week. This makes sense; whitefly population abundance can be influenced to a large extent by the crop landscape throughout Yuma. Crops planted near or adjacent to cotton and alfalfa are clearly more heavily infested than fields isolated away from these crops. In addition, our monsoon conditions often play a role where humidity and rainfall can influence population abundance. Nonetheless, you can bet heavy whitefly numbers 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. With the loss of endosulfan, growers have few options for effective residual control of adults, but good knockdown can be achieved on lettuce and cole crops with combinations of pyrethroids tank-mixed with Orthene, Lannate, Lorsban, Venom, Scorpion, or Sequoia. In addition, Exirel (the foliar formulations of Cyazypyr) was recently labeled for use on produce crops and can provide excellent adult control. Sometimes it can be difficult to determine whether a product is working 3-4 days following application when adult whiteflies are continuously moving into you field from outside sources. 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 early October. Local research has shown that imidacloprid applied at 0.25 lbs AI/ac at planting provides less residual control of nymphs today than it did 10 years ago. However, given the current economics of imidacloprid, cost-effective whitefly control can still be achieved by using higher rates of imidacloprid (0.38 lbs. AI/ac) to extend residual control (e.g., Alias 2F-24 oz; Wrangler 4F-12 oz; Admire Pro- 10.5 oz). Verimark, the soil formulation of Cyazypyr, 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- 2014 and Insect Management on Desert Vegetables and Melons: Whitefly.

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To contact John Palumbo go to: jpalumbo@ag.arizona.edu