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Entomologist’s surveys reveal trends in pesticide use

University of Arizona's John Palumbo has 19 years of research.

Todd Fitchette, Associate Editor

May 31, 2024

3 Min Read
John Palumbo
University of Arizona Entomologist John Palumbo has 19 years of surveys to show pest infestations in lettuce crops and the insecticides used by farmers in the Yuma region.Todd Fitchette

Arizona pest control advisers are using more reduced-risk insecticides than in years past, based on nearly 20 years of surveys by an Extension entomologist.

John Palumbo, an entomologist with the University of Arizona, has 19 years of data showing trends in pesticide use and problematic pests in winter vegetables grown in the Yuma area. His annual surveys of PCAs are used to demonstrate the value of new pest control technologies and to provide an historic record of insect losses in those winter crops in the desert.

“A reliable estimate of insecticide use patterns is one of our most objective tools for assessing changes in management practices,” Palumbo wrote in a 2023 report on insecticide use in conventional and organic lettuce.

Growers each year battle a host of insects that can rob yields, cause processors and food buyers to reject products destined for the marketplace, or both. Over half the fall lettuce crop grown from September through November each year is treated against the beet armyworm, cabbage looper, western flower thrip, seedling and soil pests, and the corn earworm.

Winter lettuce, which is grown from December through April, tends to see over half of those acres treated to combat four pests: the western flower thrip, green peach aphid, cabbage looper, and beet armyworm, according to Palumbo’s surveys.

All of the fall lettuce crop can be treated each year against the beet armyworm, with PCAs averaging three insecticide treatments a season for the pest.

Their efforts tend to pay off as yield losses each of the past 19 seasons ranged from over 2% in the fall crop in 2005, to under 1% in most seasons since then.

Palumbo credits PCAs with properly timed insecticide applications that prevent larvae from feeding on the plants. Beet armyworm feeds on small lettuce plants during stand establishment and can severely damage those plants.

“If not controlled they can cause stand reduction and abnormal plant growth resulting in delayed harvest,” Palumbo said.

He also credits the choice of good insecticides to properly control a host of insects that could significantly damage or destroy these desert lettuce crops. The choice of effective pesticides has not always been available.

“That wasn’t the case 25-30 years ago,” he said.

Palumbo’s surveys can also show years where particular pets were problematic. For instance:

  • 2013 losses in spring lettuce from the corn earworm spiked to 2.5%

  • Losses from seedling and soil pest for fall and spring lettuce in 2005 and 2006 ranged from 1.8% to 2.7%

  • Flea beetle damage in 2022’s fall lettuce crop caused yield losses of 1.6%

In those cases, the losses, while statistically low, were significantly higher than the 19-year average. This points to the general success of industry PCAs to control insects.

These surveys continue to validate the necessity of the PCA to the vegetable industry, according to Palumbo. It also shows the active attention these produce fields gain from PCAs, who tend to scout vegetable fields multiple times a week for pests.

Pesticide choices

The reduced-risk and selective chemistries continue to gain popularity by PCAs seeking to employ integrated pest management practices that allow beneficial insects to assist in pest control. In some cases, beneficial insects can make significant strides in further reducing dangerous pest numbers below established thresholds.

Several chemistries remain quite popular in controlling insects. Foliar pyrethroids were used to treat nearly all fall lettuce, and about 88% of spring lettuce in 2023, according to Palumbo’s survey. Popular products in the battle against insects include Radiant and Sequoia, from Corteva, and Bayer Crop Science’s Movento and Sivanto insecticides.

In organic lettuce, Corteva’s Entrust insecticide is used across all acres of fall and spring lettuce. Entrust is OMRI (Organic Materials Review Institute) approved for quick knockdown and residual control of armyworms, thrips, leafminer, codling moth, cherry fruit fly, and spotted wing drosophila. It is registered in all 50 states.

About the Author(s)

Todd Fitchette

Associate Editor, Western Farm Press

Todd Fitchette, associate editor with Western Farm Press, spent much of his journalism career covering agriculture in California and the western United States. Aside from reporting about issues related to farm production, environmental regulations and legislative matters, he has extensive experience covering the dairy industry, western water issues and politics. His journalistic experience includes local daily and weekly newspapers, where he was recognized early in his career as an award-winning news photographer.

Fitchette is US Army veteran and a graduate of California State University, Chico. 

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