Whitefly management in fall vegetables

By John Palumbo, UA Research Scientist and Extension Specialist, Yuma

To date, whitefly numbers on fall melons in Yuma County have varied from very low (1-2 per leaf) in the Yuma Valley to extremely high (more than 100/leaf) in the Dome Valley-Wellton area.

The differences in whitefly abundance can be attributed largely to the crop landscape in these areas. Melon fields near or adjacent to cotton and alfalfa clearly are the most heavily infested. Last week I observed very high numbers of adults steadily moving out of a cotton field in Dome Valley that reminded me of the "whitefly clouds" of the early 1990s.

Does this mean fall crops in 2010 will experience heavy whitefly pressure? I do not know, but pest control advisors should start thinking about whiteflies and talking with growers concerning control strategies.

The key to effective whitefly management in fall crops is to prevent adult and immature populations from colonizing small plants. It is recommended that growers apply a soil neonicotinoid on early lettuce and cole crops planted near cotton, alfalfa, or in areas that historically have high whitefly numbers.

Local research suggests that imidacloprid (Alias, 16 oz/acre; or 0.25 lbs. active ingredient (AI)/acre) applied at planting provides less residual control of nymphs today than it did 10 years ago. This is not surprising considering the heavy neonicotinoid usage on fall and spring crops over the past 17 years.

The insecticide still provides short-term control (21-28 days), but will likely require additional foliar treatments to prevent damage, particularly on cole crops. Growers may consider using higher rates of imidacloprid (0.375 lb AI/ac), or switching to an alternative soil-applied product including Venom or Durivo.

Several foliar insecticides are available that can provide effective control of adult and immature whiteflies.

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