LAUSR

BACKGROUND Multiple-herbicide resistance in Lolium rigidum and other weed species is increasingly exerting pressure on herbicide discovery research for solutions against resistance-prone weeds. In this study we investigate: 1) the responses of L. rigidum populations and wheat to the new herbicide cinmethylin in comparison with other pre-emergence herbicides, 2) the effect of seed burial depths on cinmethylin efficacy and crop selectivity, and 3) the basis of cinmethylin selectivity in wheat. RESULTS Cinmethylin at 400 g ha-1 controls herbicide-susceptible and multiple-resistant L. rigidum, with a reduction of >85% in plant emergence and 90% in aboveground biomass. Cinmethylin provides effective control of a large number of field populations of L. rigidum with evident resistance to trifluralin. When the wheat seed is buried ≥1 cm below the cinmethylin-treated soil surface, the emergence of crop seedlings is not different from the untreated control. The organo-phosphate insecticide phorate synergizes cinmethylin toxicity in wheat, with an LD50 of 682 g ha-1 in the absence of phorate versus 109 g ha-1 in the presence of phorate (84% reduction). The synergistic effect of phorate with cinmethylin on herbicide-susceptible L. rigidum appears smaller (a 44% reduction in the LD50 of cinmethylin). CONCLUSIONS Cinmethylin is effective in controlling multiple-resistant L. rigidum and appears safe for wheat when the seed is separated at depth from the herbicide applied to the soil surface. The basis of this metabolism-based selectivity is likely regulated by cytochrome P450 monooxygenases. This article is protected by copyright. All rights reserved.