Herbicide Use in Leaf Lettuce (January 22, 2014)

Leonard Gianessi, consultant for The Crop Life Foundation, has compiled the following graph for herbicide use on leaf lettuce in California. It includes Pronamide (Kerb), Benefin (Balan), Bensulide (Prefar), Clethodim (Select), Sethoxydim (Poast) and Paraquat (GRamoxone). It is possible to get this kind of data in California, which is recognized as having the most comprehensive pesticide reporting requirements in the world. Arizona requires that all commercial applications be reported to the state but does not require that all applications, including private applications, be reported. It is not possible then, to compare this California data to Arizona at the current time. As expected the use of Kerb on leaf lettuce dropped rapidly four years ago when the registration was canceled. Prefar use has increased steadily over the last 15+ years but is far short of filling the gap left by the loss of Kerb. This demonstrates that Kerb, Prefar and Balan each have a unique role in controlling weeds in lettuce.

Benefin(Balan) is used before planting and must be mechanically incorporated. It is mainly use to control grasses and some small seeded broadleaf weeds. It is rarely used alone and is primarily used to supplement one of the other two pre-emergent lettuce herbicides. Bensulide (Prefar) is normally used after planting and before irrigation has started . It is used before irrigation because it works best with large amounts of water applied over the top to incorporate it into the soil. It is used to control several annual grasses, goosefoot, lambsquarters, and purslane. Pronamide(Kerb) is used after planting and after irrigation has started. Unlike Prefar, the least amount of water used with Kerb the better it will work. It needs about ½ inch of water to be adequately incorporated but more than that will leach it below many of the germinating weed seeds. Kerb controls the broadest spectrum of grass and broadleaf weeds of the 3 preemergent herbicides used in lettuce. The loss of any of these three herbicides, especially Pronamide(Kerb), leaves a gap in the chemical weed control programs used on lettuce that can only be filled with cultivation and hand weeding.

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To contact Barry Tickes go to: btickes@ag.arizona.edu.