Effect of Repeated Application of Sulfonylurea Herbicides on Sulfosulfuron Dissipation Rate in Soil

Abstract

Accelerated microbial degradation following previous repeated applications of the same pesticide, or another pesticide of a similar chemical structure, is a known phenomenon. Currently there is limited information regarding accelerated degradation of sulfonylurea (SU) herbicides. This study is aimed to evaluate the effect of repeated SU applications on the degradation rate of the SU herbicide sulfosulfuron in soil. The effect of repeated applications of sulfosulfuron on its degradation was assessed in two soils, using a sorghum root elongation bioassay. The effect of consecutive applications of sulfonylurea herbicides over the course of three to four seasons was further examined in controlled environment and a field study. Degradation of sulfosulfuron was determined following its application to soil samples from the field or a controlled environment, by measuring sulfosulfuron residues using liquid chromatography-tandem mass spectrometry. Following the repeated application of sulfosulfuron in the bioassay, the time to reduce sorghum root growth by 50% was shortened by up to 31.6%. However, consecutive application of SUs in the controlled environment had no effect on sulfosulfuron degradation rate constant. Yet, sulfosulfuron degradation rate was enhanced by a factor of 1.35 following consecutive application of SUs in the field, compared to untreated control soil. The data confirm that sulfosulfuron degradation could be enhanced due to repeated sulfosulfuron applications, thus potentially reducing its herbicidal efficacy.