Role of temperature in the activity of acetanilide herbicides on threePhaseolustaxa

Alachlor [2-chloro-N-(2,6 diethylphenyl)-N-(methoxymethyl) acetamide], metolachlor [2-chloro-N-(2-ethyl-6- methylphenyl)-N-(2-methoxy-1 -methylethyl) acetamide] and acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6- methyl-phenyl) acetamide], members of the chloroacetanilide herbicides, are used pre-emergence to control grasses and some broadleaf weeds. Two concentrations, i.e. 0,5 and 2 mg ai kg−1 of the above herbicides did not inhibit germination of three Phaseolus bean taxa. Hypocotyl-epicotyl growth was reduced by increased herbicide concentrations between 0,5 and 2 mg ai kg−1 and increased temperatures (18 to 25°C). Significantly higher phytotoxicity was observed at 25°C than at 18°C. The order of phytotoxicity was acetochlor > alachlor > metolachlor. Acetochlor (1,5 mg ai kg−1) at 25°C reduced Phaseolus vulgaris L. cv. Kamberg hypocotyl—epicotyl growth by 42%, Phaseolus vulgaris L. cv. Bonus by 16% and Phaseolus coccineus var. albonanus (Large white kidney) by 17%. At 18°C, acetochlor (1,5 mg ai kg−1) reduced hypocotyl—epicotyl growth of Kamberg by 27%, Bonus by 24% and Kidney by 18%. Higher herbicide concentrations increased bean injury as assessed by dry mass production during hypocotyl-epicotyl growth.