SOIL PERSISTENCE OF THIAMETURON (DPX M6316) AND PHYTOTOXICITY OF THE MAJOR DEGRADATION PRODUCT

Abstract

The persistence of the herbicidal ester (14C)thiameturon was studied at different temperature and moisture conditions in three Saskatchewan soils. In all soils at 20 °C and 85% field capacity, the (14C)ester underwent rapid hydrolysis to (14C)thiameturon acid. The hydrolysis was over 85% complete in 1 week, and more than 95% complete after 2 wk. The soil degradation of (14C)thiameturon acid was considerably slower than that of the parent ester. Transformation of (14C)thiameturon to acid in all soils at 85% field capacity was temperature dependent, being slowest at 10 °C, and fastest at 30 °C. Conversion to the acid was also moisture dependent. There was no hydrolysis in air-dry soils after 10 wk. At 50% field capacity 22% of the ester remained after 1 wk, and at field capacity less than 2% of the applied ester was recoverable after 1 wk. Soils treated with thiameturon acid at rates up to 500 μg g−1 exhibited no phytotoxicity to canola, lentil, or sugarbeet seedlings. Key words: Herbicide, thiameturon, persistence, phytotoxicity