Cinmethylin controls multiple herbicide-resistant Lolium rigidum and its wheat selectivity is P450-based

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: (i) the responses of L. rigidum populations and wheat to the new Herbicide cinmethylin in comparison with Other pre-emergence herbicides, (ii) the effect of seed burial depths on cinmethylin efficacy and crop selectivity, and (iii) 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 organophosphate 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. © 2020 Society of Chemical Industry.

Lolium rigidum; cinmethylin; herbicide resistance; phorate; selectivity.