Sensitivity of selected dry bean (Phaseolus vulgaris L.) cultivars to mesotrione in a simulated carry-over trial

Abstract

Mesotrione is used to control annual broadleaf weeds and grasses in maize, with waiting periods up to 24 months recommended prior to planting sensitive crops. The objectives of this study were to determine if selected dry bean cultivars exhibited differences in sensitivity to mesotrione, and the lowest concentration that would cause significant damage. A pot trial was carried out using two small white canning bean and six red speckled bean cultivars. Mesotrione was applied at 51.2, 1.6, 5 × 10⁻², 1.5 × 10⁻³, 4.9 × 10⁻⁴, 1.5 × 10⁻⁶, 4.8 × 10⁻⁸ and 0 µg kg⁻¹ soil. Numbers of days to emergence, number of emerged seedlings as well as phytotoxicity symptoms were monitored, with plant height and mass determined at harvest. Symptoms varied from bleaching and necrosis at the higher rates, through to malformed and crinkled leaves. Highly significant effects due to both cultivar and mesotrione rate were noted on plant height, as well as a highly significant interaction effect on dry mass. The 270-day waiting period prior to planting dry beans appears to be sufficient to avoid damage to the cultivars tested on the soil type used. Although cultivar differences in sensitivity were noted, no distinct groups could be identified.