Dermatitis from poison ivy is an important health problem, and considerable effort is devoted to the control of this virulent weed. Triclopyr, metsulfuron, and two fixed-ratio tank mixtures of triclopyr and metsulfuron were evaluated across a series of rates for poison ivy control. The objective was to test whether tank mixtures are more effective than triclopyr alone. Triclopyr, metsulfuron, and 9 : 1 and 8 : 2 (by weight) mixtures of these two herbicides, respectively, were applied at eight rates to 1-yr old, pot-grown poison ivy plants. Rates ranged in phytotoxicity from none to death. Percentage of control as determined from plant fresh weight reduction relative to a nontreated control was determined at 1 and 4 mo after treatment (MAT). Data were subjected to ANOVA followed by nonlinear regression. Rates required for 95% control at 1 MAT, control of regrowth at 4 MAT, and the costs of these treatments were determined for the herbicides applied alone and the mixtures. Triclopyr alone and metsulfuron alone were consistently the least and the most expensive treatments, respectively. The mixtures were intermediate to these extremes.

Dermatitis from poison ivy is a significant health problem. Considerable effort is devoted to the control of this invasive and virulent weed in urban areas. Glyphosate, triclopyr, 2,4-D, a 1 : 1 mixture of glyphosate and 2,4-D, and a 9 : 1 mixture of glyphosate and triclopyr were evaluated for poison ivy control. Each of these three herbicides and two mixtures were applied at nine or ten rates, which ranged in phytotoxicity from none to death. Poison ivy plants had been propagated and container-grown. Percent control, as determined from plant fresh weight reduction, was determined at 1 and 4 mo after treatment (MAT). Data were subjected to ANOVA followed by nonlinear regression. Rates required for 95% control at 1 and 4 MAT and the associated costs were determined for each of the three herbicides and two mixtures. Acceptable control (i.e., ≥ 95%) at 1 and 4 MAT could be obtained at a much lower cost with either triclopyr or 2,4-D than with either glyphosate alone or with the two glyphosate-containing mixtures. Nonlinear regression also was used to evaluate whether the two mixtures were interactive (i.e., synergistic or antagonistic) or not (i.e., additive). Glyphosate plus triclopyr was synergistic for control at both 1 and 4 MAT. Glyphosate plus 2,4-D was synergistic for control at 4 MAT only. However, for both mixtures, synergism was only evident at rates that controlled poison ivy ≤ 80%. Both mixtures were noninteractive at rates required for acceptable control.

Poison ivy is a virulent weed that is frequently treated with herbicides. Dicamba, 2,4-D, and two fixed-ratio tank mixtures of dicamba plus 2,4-D were evaluated across a series of rates for poison ivy control. Objective was to test whether tank mixtures were more effective than either herbicide applied alone. Dicamba alone, 2,4-D alone, a 1 : 3, and a 3 : 1 ratio (by weight) mixture of dicamba plus 2,4-D, respectively, were applied at eight rates to 2-yr-old, container-grown poison ivy plants. The eight rates ranged from 0.036 to 1.79 kg ae ha−1, which, in terms of phytotoxicity, generally ranged from none to death. Percentage of control was determined from plant fresh-weight reduction relative to a nontreated control and was determined at 1 and 4 mo after treatment (MAT). Rates required for 95% control at 1 MAT and for control of regrowth at 4 MAT and the cost of those treatments were determined for the dicamba and 2,4-D applied alone and in the two mixtures. At the 1-MAT evaluation, 2,4-D alone was more cost effective than either dicamba alone or the two mixtures. By the 4-MAT evaluation, however, which followed clipping at 3 MAT, dicamba alone was more cost effective than either mixture. The 2,4-D alone failed to provide 95% control at the 4 MAT evaluation, even at the highest rate evaluated (1.79 kg ha−1). Response curves for the two mixtures were equivalent to the response curves of the components applied alone at the 1 MAT evaluation and fell between the response curves of the components at the 4 MAT evaluation. Hence, 2,4-D plus dicamba mixtures were neither antagonistic nor synergistic. Results indicate that dicamba applied alone is far more effective than 2,4-D is for control of established and perennial poison ivy, assuming the intent is to obtain control with a single, one-time application.