Tolerance of Winter Wheat (Triticum aestivum L.) and Under Seeded Red Clover (Trifolium pretense L.) to Fall Applied Post-Emergent Broadleaf Herbicides

The fall application of post-emergent (POST) herbicides on winter wheat provided effective control of emerged winter annual, biennial, and perennial broadleaf weeds. In recent years, wheat producers have seen a shift to these weeds, due in part, to the adoption of reduced-and no-tillage practices and the use of non-residual herbicides such as glyphosate in the preceding soybean and corn crops. The tolerance of winter wheat to ten herbicides, applied POST in the fall, was evaluated between 2008 and 2011 at Exeter and Ridgetown, Ontario. Winter wheat yield was not reduced by applications of MCPA ester, dicamba/ MCPA/ mecoprop, clopyralid, bromoxynil/ MCPA, thifensulfuron /tribenuron +MCPA ester, fluroxypyr +MCPA ester, and pyrasulfotole/ bromoxynil. In contrast, 2,4-D ester and dichlorprop/2,4-D, caused visible injury in June and July of the following year and consistently decreased winter wheat yield by at least 10%. Applications of 100 g a.i. ha-1 saflufenacil also decreased winter wheat yield in two of the four harvest years examined. None of the herbicide options examined were safe on red clover when it was under seeded the spring following winter wheat planting. All herbicides significantly decreased red clover dry biomass one month after wheat harvest.