Protecting Lettuce from Insects

No one wants to find a worm in bagged lettuce.

This observation from John Palumbo, an entomologist with University of Arizona Extension, sums up the zero-tolerance nature of growing this high-value crop. In a market where quality is key, utilizing effective tools allows lettuce growers to produce crops that meet stringent standards, reducing market rejections and maximizing profits.

Pests Abound Year-round

Palumbo conducted a nine-year survey on lettuce insect losses and insecticide use in the Yuma, Arizona, and Imperial County, California, winter lettuce regions. He surveyed growers, pest control advisers, extension personnel and industry professionals who attended workshops in Yuma.

More than 95 percent of fall lettuce acreage required insecticide treatments every year. PCAs estimated that the lepidopteran larvae complex — beet armyworm, corn earworm and cabbage looper — was the most consistently present pest on fall lettuce and required the most insecticide treatment. Thrips, whiteflies and seedling pests were also prevalent.

In spring lettuce, PCAs said the lepidopteran larvae complex is still important, but not at the same intensity as in the fall.

Meeting the Zero Tolerance Standard

Tom Turini, a University of California Cooperative Extension farm advisor for vegetables in Fresno County, said there's a different pest philosophy when it comes to lettuce. In alfalfa, for example, there’s no intention of having an insect-free crop, but with lettuce, there’s no tolerance.

“It can require a fairly intensive program for insect management, especially for the fall crop,” Turini said.

Surveys showed that lettuce growers average 4.1 and 3.1 field visits per week, respectively, in the fall and spring. Average scouting costs were estimated at more than $20 per acre over the last nine years, Palumbo said.

Farm advisors stress the importance of scouting for pests, though costly, and monitoring insect levels and spraying as needed when populations reach certain levels. Spraying for lettuce pests may be necessary eight to 10 days after lettuce emerges from the ground, Palumbo said.

Lettuce can be treated with Movento^® insecticide, which provides protection through its unique, two-way systemic movement, allowing for movement upward and downward throughout the plant’s tissue system for allover protection.