Trends in Insecticide Usage on Arizona Lettuce (May 28, 2014)

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 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. No surprise there. Over the past 10 years, pyrethroid usage has remained steady. This makes sense because they are one of the few inexpensive, broad spectrum insecticides still available for use in tank-mixtures for control of flea beetles, crickets, plant bugs and cabbage looper. The overall use of OPs and carbamates continues to decline, but Lannate and acephate are still relied upon for thrips management. Their usage is being replaced primarily by several reduced-risk chemistries, of which the spinosyns remain the second most commonly used class of insecticides. In 2013-2014, 95% of the lettuce acreage in our area was on average treated with 2 applications of Radiant or Success. Their use against both lepidopterous larvae and thrips has remained steady since they were first registered. Diamides applied as foliar sprays were the third most commonly chemistry used in lettuce this season, surpassing the neonicotinoids. The diamides were first registered in 2008, and since then PCAs have steadily incorporated this new chemical class into their management programs. Soil diamide (Coragen) usage peaked in fall 2012, but was down by about 50% in 2013. Ketoenol usage (Movento) on fall lettuce was down compared to 2010, but usage as an aphicide on spring lettuce remains around about the same. Another important chemistry used in fall and spring lettuce is the neonicotinoid class whose usage is driven primarily by imidacloprid when applied as an at-plant, soil insecticide for whitefly and aphid control. The usage of imidacloprid on both fall and spring lettuce has increased markedly since 2009 and is used on almost 90% of the acreage, albeit at higher rates. Two new products were registered this year, Closer and Torac. Closer was used on more than 10% of spring acres and Torac on less than 5%. To view a summary of the estimated insecticide usage by chemical class, as well as the 12 most commonly used insecticides on head lettuce this past growing season, go to rends in Insecticide Usage on Arizona Lettuce.