Responses of winter wheat (Triticum aestivum L.) to autumn applied post-emergence herbicides

The adoption of new production practices such as no-till and the use of non-residual herbicides such as glyphosate in the preceding crop has resulted in an increase of winter annual, biennial, and perennial weeds in winter wheat in Ontario. Few post-emergence (POST) autumn applied herbicide options are available to control these weeds. Five field trials were conducted in Ontario to evaluate the POST application of dicamba at 140 and 280 g ai/ha, 2,4-D amine, MCPA amine, dichlorprop plus 2,4-D ester, bromoxynil plus MCPA ester, and thifensulfuron-methyl plus tribenuron-methyl. The autumn POST application of dicamba, MCPA amine, bromoxynil plus MCPA ester, and thifensulfuron-methyl plus tribenuron-methyl did not cause any visual injury and there was no decrease in winter wheat height or yield. The POST application of 2,4-D amine and dichlorprop plus 2,4-D ester caused minor visual injury at 24–31 weeks after treatment (WAT). Winter wheat height was reduced as much as 8% with the POST application of dichlorprop plus 2,4-D ester. Yield was reduced up to 9% and 14% with the POST application of 2,4-D amine and dichlorprop plus 2,4-D ester, respectively. Based on these results, the POST application of 2,4-D amine and dichlorprop plus 2,4-D ester premix in the autumn results in unacceptable injury in winter wheat. However, dicamba, MCPA amine, bromoxynil, MCPA ester, and thifensulfuron-methyl plus tribenuron-methyl have an adequate margin of crop safety for use in weed management in winter wheat in Ontario.