Absorption and Metabolism of Metribuzin in Barnyard Grass and American Nightshade

The absorption and metabolism of C14-metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5 (4H) one] was studied in barnyard grass (Echinochloa crusgalli (L.) Beauv.) grown in soil or aqueous solution and in American nightshade (Solanum americanum L.) grown in aqueous solution containing radioactive metribuzin. Barnyard grass (BG) plants did not lose any radioactive CO2 in respiration and the total dry weight per plant was not affected by metribuzin. A major portion of the radioactivity recovered from BG plants was found in a compound which had approximately the same chromatographic properties as standard metribuzin. A negative correlation was obtained between the total radioactivity of metribuzin per gram of dry matter and age of both BG and American nightshade (AN) plants, but the degradation of metribuzin was significantly higher in AN than BG. Both plant species gained tolerance to metribuzin with age.