Pre-emergence herbicides for weed control in lettuce

California lettuce growers spend $11,620,000 per year for weed control. Although mechanical cultivation will control weeds in the furrow and between rows, weeds in the seed row are still controlled by hand chopping at approximately $20 to $60 per acre. With increased costs and difficulties of obtaining qualified field labor, more and more emphasis has been put on mechanical thinning and chemical weed control. Inasmuch as the more successful mechanical lettuce thinners do not distinguish between plants in general, weeds cannot be tolerated in the seed row and therefore can be eliminated most economically by selective chemical weed control. Some satisfactory weed control over the years has been obtained with the use of Vegadex and IPC with certain weed species. Several new herbicides have promised a wider spectrum of weed control, and are being used to a limited extent for weed control in lettuce. Balan and Dacthal were used last year commercially and Prefar was used in experimental plantings. Balan was recommended this year by University of California for weed control in lettuce.