Persistence of imidazolinone herbicides and effects on corn and sorghum succeeding crops

Abstract

During the 1994/95 and 95/96 farming seasons, two field assays were conducted in Coimbra, Minas Gerais, to evaluate the residual effect in soil of the herbicides imazamox (50 and 100 g/ha), imazaquin (140 and 280 g/ha) and imazethapyr (100 and 200 g/ha), used in soybean, on corn and sorghum crops succeeding soybean. Bioassays using sorghum as test-plant were conducted under greenhouse conditions by using soil samples collected from plots sprayed with the herbicides in field experiments. Soil samples were collected at 90, 105, 120 and 135 days after application (DAA) for imazamox and imazethapyr and at 95, 110, 125 and 140 DAA for imazaquin. Corn and sorghum sowing was carried out in the plots previously used for soybean crop. The results obtained allowed to conclude that imazamox had the lowest residual effect in soil among herbicides evaluated, having no influence on the development of the test-plant at 120 DAA, even when the recommended dosage was doubled. However, imazethapyr applied at 200 g/ha (double recommended dosage) inhibited significantly the development of sorghum plants sowed 120 and 135 DAA. However, in field conditions, no negative effect was observed either on corn or sorghum crops sowed 150 DAA of herbicides.