UPTAKE, TRANSLOCATION, METABOLISM, AND THE EFFECTS OF METOLACHLOR ON YELLOW NUTSEDGE AND CORN

The purposes of this study were to evaluate the effects of alachlor {2-chloro-2',6'-diethyl-N-(methoxymethyl)acetanilide} and metolachlor {2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide} on yellow nutsedge tuber viability, determine the depth of placement in the soil where uptake of metolachlor produced the greatest phytotoxicity to corn and yellow nutsedge, assess the influence of temperature on metolachlor's activity, study absorption and translocation patterns of metolachlor in corn and yellow nutsedge, and also evaluate how these plants metabolize metolachlor.;When metolachlor was incorporated at 1 ppmw in the tuber zone or above the tuber in the soil placement study, the growth of nutsedge shoots was reduced 100% and 70%, respectively. Corn injury occurred only when metolachlor was incorporated above the seed. The 10 ppmw rate of metolachlor used with corn reduced its shoot growth about 65%. With both yellow nutsedge and corn, absorption of metolachlor by the emerging shoot produced the greatest phytotoxicity.;Temperature increased the activity of metolachlor. Reductions in nutsedge shoot height of 45%, 70%, and 80% occurred at 25 C, 30 C, and 35 C, respectively, with a 1 x 10('-12) M concentration of metolachlor. Metolachlor at a 1 x 10('-4) rate reduced corn shoot height 18% and 26% at 30 C and 35 C, respectively, but no reduction occurred at 25 C. Metolachlor was toxic to yellow nutsedge at a lower temperature than with corn. Nutsedge was found to be extremely sensitive to very low rates of metolachlor.;Differences in absorption and translocation of ('14)C-metolachlor occurred not only between corn and yellow nutsedge but also between the three sites of application of the herbicide. Metolachlor was mixed into the nutrient solution for root absorption, or spotted on either the base or tip of the shoot for shoot absorption. Throughout the study corn root absorption of ('14)C at the 12, 24, and 48 hour evaluation dates was twice that of nutsedge root absorption. Both plants apoplastically translocated to the shoot less than 1% of the ('14)C. Translocation with the two shoot applications in both plants followed typical apoplastic and symplastic patterns of translocation. Nutsedge by 48 hours absorbed 6 and 12 times more ('14)C with the base and tip of shoot applications, respectively, than did corn. Nutsedge translocated 8 and 3 times more label from the base and tip of shoot applications, respectively, after 48 hours than did corn.;In a greenhouse study, 1 and 4 ppmw rates of alachlor or metolachlor did not cause a 100% reduction in yellow nutsedge tuber viability when evaluated after 3, 6, and 9 weeks. Metolachlor was more active than alachlor at comparable rates in reducing nutsedge growth.;Metabolism of metolachlor also differed between corn and yellow nutsedge and between the three sites of application. Nutsedge metabolized only 15% of the metolachlor with either shoot application after 12 hours while corn metabolized over 90% of the parent compound with the two shoot applications after the same time period. Metolachlor applied to the tip of a nutsedge shoot was metabolized faster than with a basal application. Seven minor metabolites were common to both shoot sites of application with nutsedge. Only 3 metabolites were common to all three sites of application in corn, even though corn metabolized metolachlor to more metabolites than nutsedge. Metabolite 12 was the main corn metabolite for all three sites of application and it was non-polar in nature.