As anticipated, whitefly numbers on fall melons have been very high in the Yuma Valley, and extremely high (> 100 / leaf) in some areas of Dome Valley, Wellton and further east. This high whitefly abundance can be attributed largely to the crop landscape in these areas where melon fields near or adjacent to cotton and alfalfa clearly are the most heavily infested. Last week, high numbers (clouds) of adults were seen in Dome Valley that were reminiscent of the early 1990's. Given that whiteflies were quite damaging last fall in produce and melon crops, PCAs would be wise to pay particular attention to early whitefly control and discuss control strategies with their 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, and on seedling lettuce plants, prolonged adult feeding can result in stunted growth. Furthermore, 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 melons crops. Because of these high numbers this year it is strongly recommended that growers apply a soil neonicotinoid on lettuce and cole crops throughout 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 like Movento, Venom, Scorpion, Assail, Knack and Courier can provide effective control of nymphs. For control of adults, 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 please read Insect Management on Desert Vegetables and Melons: Whiteflies and the Whitefly Control Chart for this fall.

Adult SPWF Bemisia tabaci

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

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.