PHYTOTOXICITY AND PERSISTENCE OF CHLORSULFURON, METSULFURONMETHYL, TRIASULFURON AND TRIBENURON-METHYL IN 3 SOILS

Bioassay procedures, based on the root growth of maize (Zea mays L.), sunflower (Helianthus annuus L.), lentil (Lens esculenta M.) and sugar -beet (Beta vulgaris L.) were used to study the phytotoxicity and pers istence of the herbicides chlorsulfuron, tribenuron-methyl, triasulfur on, and metsulfuron-methyl as affected by concentration and soil type. All bioassays indicated that phytotoxicity of all herbicides was not affected by soil texture but was increased with increasing herbicide c oncentration and soil pH. Chlorsulfuron and metsulfuron-methyl showed the highest phytotoxicity, and tribenuron-methyl the lowest; triasulfu ron indicated intermediate phytoxicity. Sugar-beet was found to be the most sensitive crop to all four herbicides, while maize and sunflower were the least; lentil showed intermediate sensitivity. The relations hip between phytotoxicity and herbicide concentration was best describ ed by a quadratic equation. Concerning field persistence, the results indicated that persistence and leaching of all herbicides in all soils increased with increasing rate of application, except for tribenuron- methyl in the sandy clay loam soil where they were very low. Sunflower , lentil and sugar-beet sown 8 months after herbicide application in t he sandy loam soil were not affected by tribenuron-methyl, but were in jured by all the other herbicide treatments. These three crops and sun flower sown at the same time in the sandy clay loam and silty clay loa m soils, respectively, were not affected by any treatment while lentil and sugar-beet were injured by chlorsulfuron in the silty clay loam s oil only.