The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz., released Sept. 7, 2011.

Whitefly management on fall vegetables and melons

By John Palumbo, UA Research Scientist and Extension Specialist

Whitefly numbers on fall melons have been very high in the Yuma Valley, and extremely high (>100/leaf) in some areas of the Dome Valley, Wellton, and further east. This high whitefly abundance is attributed largely to the crop landscape where melon fields are near or adjacent to cotton and alfalfa.

During the week of Aug. 29, high numbers (clouds) of whitefly adults were seen in Dome Valley reminiscent to the early 1990s.

Since whiteflies were quite damaging last fall in produce and melon crops, pest control advisers would be wise to pay particular attention to early whitefly control and discuss control strategies with growers.

Remember, the key to effective whitefly management in fall crops is to prevent adult and immature populations from colonizing small plants.

Prolonged feeding by adults on melons can rapidly spread virus throughout the field. On seedling lettuce plants, prolonged adult feeding can result in stunted growth.

Allowing adults to remain on plants unchecked generally results in the development of large nymph populations which can cause significant growth/yield reductions in all produce and melon crops.

With the high numbers this year, it is strongly recommended that growers apply a soil neonicotinoid on lettuce and cole crops in September and early October.

Local research has shown that imidacloprid (e.g., Alias-16 oz, or Admire Pro- 7 oz ; [0.25 lbs AI/ac]) applied at planting provides less residual control of nymphs today than it did 10 years ago. Although the insecticide still provides short-term control (21-28 days), growers should consider using higher rates of imidacloprid (e.g., Alias-24 oz, or Admire Pro- 10.4 oz [0.375 lb AI/ac]) to extend residual control.

Once plants get larger, products including Movento, Venom, Scorpion, Assail, Knack, and Courier can provide effective control of nymphs.

For adult control, combinations of bifenthrin (e.g. Brigade, Sniper, Discipline, etc.) or Danitol tank-mixed with Thionex will provide the best residual control.

Other options that can be tank-mixed with pyrethroids for knockdown control include Vydate, Orthene, Lannate, Lorsban, Dibrom, Venom, Scorpion, and Assail.

For more information on whitefly biology, management, and insecticide alternatives, review these links: Insect Management on Desert Vegetables and Melons: Whiteflies and the Whitefly Control Chart.

Contact Palumbo: (928) 782-3836 or jpalumbo@ag.arizona.edu.