The three main lettuce herbicides, Balan, Prefar and Kerb all have the same mode of action but should be used differently to achieve the maximum weed control and crop safety. All three kill weeds by stopping cell division in seedling weeds but they differ in how they move in soil and plants.

Balan (Benefin) adheres very strongly to many soils and cannot be moved with water alone. Most weeds that emerge with the lettuce are located within the top half inch of soil. It is difficult to move Balan even a quarter inch into the soil with sprinkler irrigation and impossible with furrow irrigation. Balan must be mechanically incorporated. It is normally applied and mechanically incorporated prior to listing the beds. Mechanically incorporating Balan after listing will concentrate this herbicide into the bed top and increase weed control but will also increase the possibility of crop injury. Balan is the most active of the dinitoaniline herbicides which include Treflan, Prowl and Balan and care should be used when concentrating it near the crop seed.

Prefar (Bensulide) also adheres strongly to many soils and is difficult to move down to the germinating weed seeds. Mechanical incorporation often dilutes this herbicide and reduces weed control. It is most effective when a concentrated layer is moved into the soil with overhead sprinklers. Tests have demonstrated that increasing amounts of sprinkler irrigation water improves weed control. Furrow irrigation does not incorporate this herbicide and results in poor weed control. Prefar can be effectively incorporated when chemigated through sprinklers.

Kerb (Pronamide) differs from Balan and Prefar because it does not adhere strongly to most soils. It is common to leach Kerb below germinating weed seeds in the low deserts where relatively large amounts of water are used to germinate the crop. It has become a common practice to delay application of this herbicide until just before or after weed seeds germinate. Kerb also differs from Balan and Prefar because it moves or translocates in plants. It can move from the roots upward to the stems and leaves and downward from the leaves to the roots. It can kill sensitive weeds postemergence when they are very small. Prefar and Balan do not move in plants and work only on the root tips that contact them in the soil. They stop root growth at the point of contact but do not translocate to other parts of the plant. More information on this subject can be found 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.