Control of grassy weeds in annual canarygrass

There are currently no herbicides registered in Argentina for the selective control of grassy weeds in annual canarygrass (Phalaris canariensis L.). The principal grassy weeds are darnel ryegrass (Lolium temulentum L.) and wild oats (Avena fatua L.), which cause grain yield and quality losses. The potential of diclofop-methyl and clordinafop-propargyl for their control was assessed through greenhouse and field trials, in which crop phytotoxicity and weed control efficacy were evaluated. It was found that (i) field application of clordinafop-propargyl resulted in severe crop damage, except for low doses that did not affect the species to be controlled; (ii) although field application of diclofop-methyl resulted in a certain degree of phytotoxicity on wild oats, these effects were insufficient for efficacious control; and (iii) field and greenhouse application of diclofop-methyl between 200 and 500 g a.i. ha−1 revealed differences between crop sensitivity and that of darnel ryegrass. In this range, crop phytotoxicity in the greenhouse was less than 20% compared to more than 60% in the weed, and in the field only slight crop phytotoxicity symptoms were observed. As in the greenhouse, field application resulted in significant phytotoxic effects upon darnel ryegrass, high efficacy levels, a low survival rate amongst treated plants and a notable reduction in seed production by surviving plants. Only the highest dose (500 g a.i. ha−1) in one of the field trials resulted in a significant reduction in crop grain yield. Hence diclofop-methyl application appears to offer a promising means for controlling darnel ryegrass.

Research highlights
► Control of darnel ryegrass and wild oats in the crop annual canarygrass was studied.
► Clordinafop-propargyl gave severe crop damage and so was not further studied.
► Diclofop-methyl gave insufficient phytotoxicity on wild oats for efficacious control.
► This herbicide gave useful phytotoxic differences between darnel ryegrass and the crop.
► It also improved crop seed quality by reducing contamination with darnel ryegrass seeds.