Efficacy of 2,4-D Choline/Glyphosate Dimethylamine on Glyphosate Resistant Canada Fleabane (<i>Conyza canadensis</i>) at Different Sizes

Abstract

Glyphosate resistant (GR) Canada fleabane has spread quickly across southwestern Ontario and new strategies for the control of this competitive weed must be developed especially in no-tillage crops. A premix of 2,4-D choline and glyphosate dimethylamine (DMA) has been developed for application on tolerant corn, soybean and cotton crops that provides an option for the control of this problematic GR weed. The objective of this research was to determine the required dose needed to effectively control GR Canada fleabane at different size categories in field and greenhouse experiments. In the field experiments, nine rates of 2,4-D choline/glyphosate DMA (53.8 to 13,760 g · ae · ha - 1 ) were applied to GR Canada fleabane that were 10 cm in diameter/tall, 20 cm tall or 30 cm tall. Similarly, in the greenhouse, seven rates of 2,4-D choline/glyphosate DMA (0 to 3440 g · ae · ha -1 ) were applied to 10, 20 and 30 cm tall GR Canada fleabane plants. The three different size classes of GR Canada fleabane responded similarly to 2,4-D choline/glyphosate DMA in the field experiment. In the greenhouse there were some differences in control for the three size classes of GR Canada fleabane with 2,4-D choline/glyphosate DMA; the 20 and 30 cm tall plants required similar rates to provide equivalent control, but the 10 cm plants required a lower rate. In all situations, greater than 1720 g · ae · ha - 1 of 2,4-D choline/glyphosate DMA was required to provide 95% control of 10, 20 and 30 cm tall Canada fleabane in greenhouse (35 DAA) and field experiments (8 WAA), respectively.