Our annual Lettuce Crop Losses Workshop was recently held in April and the results of the surveys reveal some interesting trends in insecticide usage on desert head lettuce. In general, the most commonly used insecticides in fall and spring lettuce correspond directly to the key pests that typically occur during these growing periods. When compared by class of chemistry using the IRAC mode of action classification system, the pyrethroids, applied both as foliar sprays and chemigations, were by far the most commonly used insecticide class (Tables 1, 2 and 3). This makes sense because they are one of the few inexpensive, broad spectrum insecticides still available for effective control of beetles, crickets and plant bugs. Nonetheless, over the past few years pyrethroid usage has been steadily declining, as has usage of organophospahates, and carbamates where Lannate and Orthene continue to be the primary compounds used in desert lettuce. The spinosyns remain the second most commonly used class of insecticides, where greater than 90% of the lettuce acreage was treated with Radiant and Success in 2011-2012. Their activity against both lepidopterous larvae and thrips make them a good fit in desert lettuce. The third most commonly used class of chemistry in fall and spring lettuce are the neonicotinoids driven primarily by at-plant, soil uses for sucking insects. Estimates this season showed that PCAs used generic imidacloprid and Admire Pro on a larger percentage of acres this season compared to last year. Estimates of Diamide usage (Coragen, Voliam Xpress, Vetica) showed that PCAs applied more of this chemistry in 2011-2012 than the previous season, and estimates further suggest that growers are slowly beginning to incorporate at-planting, soil uses of Coragen into their programs. Ketoenol usage (Movento) on fall lettuce was down compared to 2010, but usage as an aphicide on spring lettuce remains about the same. From an IPM perspective, the industry has made great strides in minimizing environmental impacts in lettuce production by continuing to incorporate the newer insecticides into their insect management programs. And for the second season in a row, PCAs treated a greater percentage of their acreage with selective, reduced-risk products than with the broadly toxic, older chemistries (pyrethroids, organophosphates, carbamates). To view a summary of the estimated insecticide usage by chemical class, as well as the 15 most commonly used insecticides on head lettuce during the past two growing season, go to Insecticide Use in Arizona Head Lettuce.

Remember: When in Doubt-Scout.

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.