Crop sensitivity to mesotrione residues in two soils: Field and laboratory bioassays

Abstract

Herbicide residues can potentially injure sensitive crops grown in rotation. Thus, the objective of this study was to evaluate the sensitivity of six replacement crops to mesotrione residues 1 yr after herbicide application. In field bioassay, mesotrione was applied at recommended (144 g ai ha-1), twofold (288 g ai ha-1), and fourfold (576 g ai ha-1) rates at two soil types (Gleysol and Fluvisol). In field and laboratory bioassays, mesotrione residual activity was followed for a 21-d period using various measurements of phytotoxicity. No visible injuries to mesotrione residues were observed on oat (Avena sativa L.), rapeseed (Brassica napus L.), soybean (Glycine max [L.] Merr.) and sunflower (Helianthus annuus L.) in the field bioassay. Although mesotrione residues were not detected by HPLC-UV/DAD analysis, field bioassays indicated their presence due to visible injuries on field pea (Pisum sativum L.) grown in Gleysol soil with twofold and fourfold herbicide treatments. In contrast to other test crop responses, sugar beet exhibited visible injuries in both soils, and consequently, was subjected to laboratory bioassay. With increasing mesotrione rates, the reductions in sugar beet (Beta vulgaris L. var. saccharifera Alef.) fresh weight and total carotenoids content ranged from 6.2% to 18.7% and from 4.1% to 19.4% in Gleysol, and from 1.1% to 7.7% and from 0% to 11.9% in Fluvisol, respectively. Since herbicide residues could not often be detected by instrumental analysis, the bioassays seem to be a reliable tool for crop safety assessment.