Impact of Ethoxysulfuron on Lemna gibba L. and Recovery from Damage after Prolonged Exposure under Rice Cropping Conditions

--------------------------------------------------------------ABSTRACT------------------------------------------------------The aim of the study was to determine the impact of the herbicide, ethoxysulfuron on the growth of Lemna gibba under rice field cropping conditions. During the course of the study, Lemna frond number was decreased from day 0 (1820 μg/L ethoxysulfuron) to day 30 (10 μg/L) resulting in 100% inhibition of growth. The decline in growth continued till day 50, at below the detectable level of residues, symptoms (chlorosis) of ethoxysulfuron toxicity were confirmed by pigment content analysis and toxicity index values. A significant decrease in the pigment content was observed between day 0 and day 50. From day 70, there was a consequent growth recovery and complete recovery on day 180. Our findings indicated that ethoxysulfuron and its metabolites retaining the sulfonylurea group was highly toxic to L. gibba, however, the effects are reversible after prolonged exposure due to the degradation of the metabolites.