Effects of Glyphosate Combinations by 2,4-D or Dicamba on Field Bindweed (Convolvulus arvensis)

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Abstract
Applications of isopropylamine glyphosate at 0.28, 0.56, 0.84, and 1.12 kg ae/ha in combination with the dimethylamine salts of 2,4-D or dicamba at 0.14, 0.28, 0.42, and 0.56 kg ae/ha produced additive or synergistic field bindweed control compared to the herbicides applied alone. Leaf and root growth was inhibited more from herbicide combinations than would be predicted from the effects of the chemicals applied alone at the same rate. The uptake of14C from glyphosate into the treated leaf and its accumulation in roots increased when 2,4-D or dicamba was combined with the 0.28 kg/ha rate of14C-glyphosate. The combination of 2,4-D or dicamba with a higher (0.84 kg/ha)14C-glyphosate rate did not change total absorption of14C from glyphosate. However, compared to 0.84 kg/ha of14C-glyphosate applied alone, less14C accumulated above the treated leaf and more accumulated in the roots when 2,4-D was added to the glyphosate. The combination of glyphosate with 2,4-D or dicamba generally resulted in both increased uptake of14C from 2,4-D or dicamba and greater accumulation in the roots. The additive or synergistic field bindweed control observed from mixtures of glyphosate with 2,4-D or dicamba appeared to be due to greater accumulation of the herbicides in the roots.