A novel bioassay for herbicides used in wild oat control and for the assessment of their interactions with other xenobiotics

A bioassay is described which uses young oat seedlings to determine the activity of wild oat herbicides alone and in mixtures with other xenobiotics. Test solution (10 μl) was pipetted into the first leaf sheath of the oat seedlings, and 24 to 48 h later, basal shoot sections were removed and cultured for 24 h on agar. The inhibition of leaf growth from these sections, compared with control sections, was an assessment of herbicidal activity. Marked inhibition occurred when as little as 0–5 to 1 -0 μg of either diclofop-methyl or diclofop had been applied to each plant. Wheat and barley seedlings were unaffected by 12 μg of these herbicides, reflecting their known selectivity in cereal crops. The assay was used to evaluate the antagonisms of diclofop-methyl and diclofop activity by 2,4-D, MCPA, 2,3,6-TBA and also related ‘non-auxins’ (3,5-dichloro-phenoxyacetic acid and 2,3,5-TIBA). Diclofop-methyl was compatible with the 1-methylheptyl ester of (4-amino-3,5-dichloro-6-fluoro-2-pyridyl)oxyacetic acid (Dowco 433). The test allows the simultaneous examination of herbicidal responses and related metabolic changes in the oat tissue. As the procedure uses small amounts of chemical, it is suitable for ¹⁴C tracer studies and other investigations for v/hich research chemicals are not freely available. The use of the test with other species and other herbicides is discussed, and possible applications for screening for crop safeners and investigations on crop tolerance are suggested.