Soil solution pH can affect the response of the common bean (Phaseolus vulgaris L.) to mesotrione residues

Soil pH can affect the adsorption of mesotrione and exacerbate crop injury under non-acidic conditions. Soil samples collected from the same location were irrigated with water solutions of pH 7.5, 6.5, 5.5, and 4.5 and treated with 72, 36, 24, 18, 9, 4.5, 2.3, and 1.1 g a.i. (active ingredient) of mesotrione/ha. Bean growth was monitored over 28 days. Soil pH solution did not influence the effect of mesotrione on plant fresh weight, while herbicide-induced visual injury and reduction in carotenoid content were significantly mitigated under acidic conditions. The lowest rate (1.1 g a.i./ha) applied in slightly acidic soil (pH 6.5) caused visual injury of 45% 28 days after treatment, while visual injuries on plants grown in soils with pH 4.5 were only 20%. Further, bean plants grown at pH 4.5 showed only 3.3% lower carotenoid content compared to control plants since for those grown in a slightly alkaline environment (pH 7.5) reduction of this pigment was 35.5%. The mean effective dose (ED50 ± standard error) of mesotrione for inhibition of carotenoids were 5.25 ± 0.61 g a.i./ha at pH 7.5, 9.57 ± 0.74 g a.i./ha at pH 6.5, 13.07 ± 0.91 g a.i./ha at pH 5.5, and 14.98 ± 0.94 g a.i./ha at pH 4.5. Results indicate that the common bean is highly susceptible to the presence of mesotrione residue and that this sensitivity strongly depends on soil pH solution.