Differential Toxicity, Absorption, Translocation, and Metabolism of Metolachlor in Corn (<i>Zea mays</i>) and Yellow Nutsedge (<i>Cyperus esculentus</i>)

Abstract

Metolachlor [2-chloro- N -(2-ethyl-6-methylphenyl)- N -(2-methoxy-1-methylethyl)acetamide] toxicity, absorption, translocation, and metabolism were investigated in corn ( Zea mays L.) and yellow nutsedge ( Cyperus esculentus L.). Metolachlor did not inhibit seed germination in corn or tuber germination in yellow nutsedge. It did not kill yellow nutsedge tubers that were exposed to 4 ppmw for 9 weeks. Metolachlor (10 ppmw) applied in soil above the seed significantly reduced corn shoot growth, but the same concentration around or below the seed had no effect. A soil mixture with metolachlor (1 ppmw) placed above or around yellow nutsedge tubers significantly reduced shoot growth, but placement around the tuber was the most toxic; placement below the tuber had no effect on shoot growth. The concentration of metolachlor that resulted in 50% reduction of shoot growth of 4-day-old seedlings in solution culture was &gt; 10 −4 M for corn and &lt;10 −6 M for yellow nutsedge. Root-applied 14 C-metolachlor was acropetally translocated to shoots of both species following a 7- to 13-day absorption period, with yellow nutsedge translocating the highest portion of the absorbed material to shoots. In 2-day-old seedlings with roots exposed to 14 C-metolachlor for up to 48 h, both species absorbed and translocated the radioactivity to shoots, but corn absorbed much more than yellow nutsedge. When the 14 C-metolachlor was applied to shoots of both species, the radioactivity was translocated basipetally into roots. Yellow nutsedge exuded appreciable 14 C-metolachlor out of the roots and absorbed more 14 C-metolachlor through shoot tissues than corn. Both corn and yellow nutsedge seedlings readily converted the 14 C-metolachlor to metabolites, but corn was able to metabolize the 14 C-metolachlor at a faster rate than yellow nutsedge and also produced more metabolites.