Thiameturon Phytotoxicity to Kochia (Kochia scoparia)

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Abstract
The methyl ester of thiameturon {3-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] amino] sulfonyl]-2-thiophencarboxylic acid} toxicity to kochia [Kochia scoparia (L.) Schrad. # KCHSC] increased with surfactant concentration in the spray to 0.25% (v/v). High soil nitrogen fertility (165 ppm) enhanced kochia susceptibility to thiameturon compared to low nitrogen fertility (65 ppm). Nitrogen plus surfactant in the spray only partially overcame the effect of low soil nitrogen but did enhance thiameturon toxicity to kochia at all fertilities. Petroleum oil plus surfactant enhanced thiameturon so that kochia fresh weight reduction was similar regardless of soil fertility. Thiameturon toxicity to kochia generally increased with an increase in temperature regardless of relative humidity (RH) or adjuvants. An RH of 90 to 95% enhanced thiameturon toxicity to kochia regardless of temperature or adjuvants, except for petroleum oil plus surfactant with the low (10:8 C day:night) temperature regime. A simulated rain of 2 mm within 24 h after treatment reduced thiameturon toxicity to kochia. Drought stress (≤25% of field capacity) after thiameturon application reduced toxicity regardless of spray additives. The results of the various experiments indicated that thiameturon phytotoxicity would be greatest to kochia growing with high temperature and high RH, adequate soil moisture and nitrogen fertility, and when applied with petroleum oil plus surfactant.