Phytotoxicity of several pre-emergence and post-emergence herbicides to green beans (Phaseolus vulgaris)

Abstract

The phytotoxicity to green beans (Phaseolus vulgaris) of the herbicides metolachlor, pendimethalin, cyanazine, acifluorfen, diflufenican, bentazone, metribuzin, prometryn, terbutryn, methabenzthiazuron, and oxyfluorfen was investigated in 4 experiments on a black earth soil (clay content 40-60%) at Gatton Research Station in southern Queensland during 1990-91. Metolachlor was applied post-sowing and pre-emergence; up to 4 kg a.i./ha did not significantly (P>0.05) affect growth or yields, indicating a considerable safety margin for this herbicide when used at commercial rates. Pendimethalin did not cause significant crop damage when applied in the same manner at rates up to 2.7 kg a.i./ha. Acifluorfen and diflufenican were each applied at 3 or 4 weeks after sowing in 3 experiments. Sensitivity of the bean crop to acifluorfen varied: 0.5 kg a.i./ha did not significantly reduce bean growth or yield in 2 experiments, but 0.11 kg a.i./ha reduced yields by 20% in a third experiment. Application of 0.1-0.12 kg a.i./ha of diflufenican had no adverse effect on beans in 2 experiments, although significant damage was observed in an initial screening experiment. Bentazone applied 3 weeks after sowing had no significant effect on bean yield or growth in 1 experiment; in another, the maximum label rate of 0.96 kg a.i./ha significantly reduced bean growth and yield. Post-emergence application of cyanazine, metribuzin, prometryn, terbutryn, methabenzthiazuron, or oxyfluorfen at rates required for acceptable weed control either killed the bean plants within a few days or resulted in complete yield loss. Levels of damage from these herbicides preclude their use in green beans. Although green beans showed some tolerance to postsowing, pre-emergence application of cyanazine, low rates of 0.75-1 kg a.i./ha reduced yields by 35%. Both metolachlor and pendimethalin appear suitable for pre-emergence use in green beans. Further work on factors affecting phytotoxicity of acifluorfen, diflufenican, and bentazone to green beans is required.