The same three herbicides, Kerb (Pronamide), Prefar (Bensulide) and Balan (Benefin) have been used for preemergence control of broadleaf and grass weeds in lettuce for 40 years. Poast (sethoxydim) and Select (clethodim) were registered for use on lettuce in the mid to late 1980s although these are effective only on grasses.

New herbicides have not been registered for use in lettuce and these older products have been used effectively for decades. They are all valuable and used in combination along with tillage and hand labor to achieve the high levels of weed control demanded by lettuce growers.

Kerb (Pronamide) is the most broad spectrum and widely used herbicide on lettuce. The results of an “Insect Losses Survey” conducted in Yuma Arizona in 2009 indicated that 69% of the lettuce acreage was treated with Kerb, 42% with Prefar and 33% with Balan. Rohm & Haas first registered Kerb in 1969, and the company was acquired by Dow AgroSciences in 2001. Kerb is currently labeled on head lettuce, endive, escarole and radicchio although the registration for leaf lettuce was removed in August 2009. In 2009 53% of the lettuce grown was head lettuce and 47% was leaf lettuce. This cancellation is expected to be temporary and is the result of regulatory action by the EPA and not because of any known problems with food safety or environmental contamination. Kerb is still registered on other leafy vegetables including head lettuce and has been used safely for decades on leaf lettuce. Early Kerb registrations did not differentiate between the types of lettuce and most of the early work done by Rohm and Haas was done with head lettuce. The EPA now regards leaf and head lettuce as being in different crop classifications requiring separate studies. Leaf lettuce is a major market for Kerb and Dow AgroSciences has already completed most of the required tests. Some additional tests that were not previously required are still being conducted. It takes several months from the submission of the required information until registration is approved. Full registration for leaf lettuce is expected to be reestablished some time in 2012.

If you need more information regarding this subject you may want to attend one of the upcoming meetings being conducted by Dow AgroSciences. The dates and locations can be obtained at this link.

To contact Barry Tickes go to: btickes@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.