Herbicide activity of monosulfuron and its mode of action

Monosulfuron was developed for weed control in the field of wheat(Triticum, aestivum L.) and millet(Panicum miliaceum L.) with the application rate ranging from 15 to 60 g ai/hm2. Herbicidal activity of monosulfuron was evaluated systematically by bioassay using maize(Zea mays L.) taproot as indicator and weed fresh weight of Acalypha australis L. and Echinochloa phyllopogon. Maize CAU 3138 was the most tolerant cultivars to monosulfuron with IC_ 50(concentration of 50% inhibition) of 85 μg/kg, Yedan 13 was one of the most sensitive cultivars to monosulfuron with IC_ 50 of 6.4 μg/kg. Monosulfuron inhibited the growth of Acalypha australis L. strongly comparing with that of Echinochloa phyllopogon. Monosulfuron was a good acetolactate synthase(ALS) inhibitor in vitro, the I_ 50(50% of inhibition) of monosulfuron, chlorsulfuron, tribenuron-methyl and nicosulfuron for CAU 3138 were 32, 2, 19 and 26 nmol/L respectively, for Yedan 13 the I_ 50 were 15, 3, 17 and 65 nmol/L respectively. In vivo ALS inhibition occurred only in higher concentration of 4 sulfonylurea herbicide tested. Comparison study of this test indicated that the mode of action of monosulfuron was the same as that of other sulfonylurea herbicides such as chlorsulfuron, tribenuron-methyl and nicosulfuron, they were all inhibitors targeted at the ALS.

Residue analysis and dissipation of monosulfuron in soil and wheat

HPLC-UV residue analytical method for monosulfuron [N-[( 4' -methyl) pyrimidin- 2' -yl]-2-nitrophenylsulfonyl urea] in soil and wheat was developed. Monosulfuron residues were recovered by solvent extraction, followed by liquid-liquid partition, and C 18 cartrige clean-up. Excellent method recoveries ranging from 95%—104% for both fortified soil and wheat grain were obtained with coefficients of variation 1.5%—11.8%. The minimum detectable quantities in soil and wheat were both 4 ng, the limit of detection was 0.02 mg/kg. When monosulfuron was applied according to double dosage of maximum recommended use direction(120 g ai/hm 2 of 10% monosulfuron wettable powder sprayed for once during development of wheat) in field studies conducted in Shandong Province and near Beijing, monosulfuron residues was not detected in soil and wheat samples collected 75 d after application. Laboratory soil degradation studies showed that monosulfuron degraded faster in acidic soil and strong alkaline soil than in neutral or weak alkaline soil. Half lives in Jiangxi soil, Shijiazhuang soil, Jiangsu soil and Heilongjiang soil were 41, 48, 87 and 84 d respectively. Monosulfuron residues dissipated rapidly in Shandong and Beijing field test sites with half-lives of less than 14 d.