Alachlor, metolachlor and acetochlor belong to the chloroacetanilide class of herbicides. Their main use in Wisconsin is for pre-emergence control of annual grasses in corn. Alachlor and metolachlor are also used for weed control in soybeans and certain other crops. Products containing metolachlor (Dual) and alachlor (Lasso) have been used in Wisconsin for over 25 years. Acetochlor products (Harness, Surpass) have only been in use since 1994.

In 1996, alachlor, metolachlor and acetochlor were used on 692,100; 972,500; and 351,000 acres of cropland in Wisconsin, respectively (WASS, 1997). The total amount of active ingredient applied of these three compounds was 1.15, 1.67, and 0.647 million pounds, respectively. In 1996, metolachlor was second only to atrazine in the amount of active ingredient applied to corn in Wisconsin.

Recent trends in the use of these three herbicides show that acetochlor use is increasing, alachlor use is decreasing, and metolachlor use is remaining fairly constant. These trends are expected to continue as new acetochlor products replace older alachlor products.