Behavior and Fate of Metribuzin in Soybean and Hemp Sesbania

Abstract

The absorption, translocation, and metabolism of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H) one] by soybean (Glycine maxMerr. ‘Lee 68′) and hemp sesbania (Sesbania exaltataL.) grown in nutrient solution and in soil treated with¹⁴C-metribuzin were investigated. Absorption studies indicated there were no significant differences in the amount of¹⁴C-metribuzin absorbed from treated nutrient solution by soybean (tolerant) and hemp sesbania (susceptible). When these species were grown in¹⁴C-metribuzin treated soil, hemp sesbania absorbed appreciably more herbicide than did soybean.¹⁴C-metribuzin and (or) its¹⁴C-metabolites were translocated from the roots to the shoots of both species. Radioactivity was rapidly translocated and accumulated in all the leaves of hemp sesbania, but it tended to accumulate to the greatest extent in the roots and lower leaves of soybean. Translocation differences between the two species were apparent in plants grown either in soil or nutrient solution treated with¹⁴C-metribuzin. However, differences were greatest in plants grown in treated soil. Preliminary metabolic studies indicated that a higher rate of metribuzin degradation occurred in soybean than in hemp sesbania. The major¹⁴C-metabolite appeared to be the relatively nonphytotoxic deaminated diketo derivative [6-tert-butyl-1,2,4,-triazine-3-5(2H,4H)dione]. Thus, differences in the absorption, translocation, and metabolism of metribuzin all appeared to contribute to the differential susceptibility of soybean and hemp sesbania to metribuzin.