ALACHLOR AND METOLACHLOR MOVEMENT DURING WINTER AND EARLY SPRING AT 3 MIDWESTERN SITES

This study was undertaken to empirically assess alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] movement in soils during winter and early spring. Alachlor and metolachlor were applied to frozen soils in late November or early December at Rosemount, MN and Aurora and Beresford, SD. Soils were sampled in February, March, and April or May and dissected incrementally. Herbicides moved from the surface into the soil at each site. Herbicide redistribution was greatest at the last sampling date when alachlor was measured to 105 cm. Metolachlor was less mobile than alachlor with most remaining at or above the 15-cm depth. These data indicate that most herbicide leaching occurred during the spring with water supplied by snowmelt, the melting frost lens, or spring rains.