Evaluations of Selected Herbicides and Rates for Long-Term Mugwort (Artemisia vulgaris) Control1

Abstract

Two field trials were established in Virginia during 1998, 1999, and 2000 to evaluate long-term mugwort control with varying rates of dicamba, triclopyr, clopyralid, picloram, metsulfuron, glufosinate, glyphosate, and the dimethylamine salt and the isooctyl ester of 2,4-D. A logarithmic sprayer was utilized in the first field trial to evaluate mugwort control with each of these herbicides, and, except for metsulfuron, rates ranged from 0.28 to 8.9 kg ai/ha. Mugwort control with metsulfuron was evaluated at a lower rate range. In addition, mugwort control was evaluated with a logarithmic range of pelargonic acid rates in combination with constant rates of glyphosate, glufosinate, and the dimethylamine salt of 2,4-D. Complete control of mugwort plants and rhizomes was achieved at 1 yr after treatment with picloram at rates ≥ 0.28 kg ai/ha, with clopyralid at rates ≥ 4.4 kg ai/ha, and with glyphosate at 8.9 kg ai/ha. Greater than 80% mugwort control was also achieved at 1 yr after treatment with clopyralid at rates ≥ 0.28 kg/ha, with glyphosate at rates ≥ 4.4 kg/ha, and with dicamba at 8.9 kg ai/ha. However, all rates (≤ 8.9 kg ai/ha) of glufosinate, triclopyr, and the dimethylamine salt and the isooctyl ester of 2,4-D provided less than 50% mugwort control at 1 yr after treatment. Similar results were obtained with metsulfuron at rates ≤ 0.063 kg ai/ha. The addition of pelargonic acid to glyphosate, glufosinate, or the dimethylamine salt of 2,4-D did not significantly enhance mugwort control when compared with applications of these herbicides alone. Additionally, progressively higher rates of pelargonic acid in combination with glyphosate, glufosinate, or the dimethylamine salt of 2,4-D resulted in antagonism of these herbicides. In separate field trials conducted in 2000, reduced rates of picloram were evaluated. In these dose–response trials, picloram at 0.28 kg/ha was the lowest rate that consistently provided greater than 90% control of mugwort at 3 mo after treatment. Collectively, the results from both trials indicate that excellent long-term mugwort control may be achieved with relatively low use rates of picloram (0.28 kg/ha) and clopyralid (0.28 kg/ha), but higher rates were needed for glyphosate (8.9 kg/ha) and dicamba (8.9 kg/ha). Results also indicate that little to no long-term control of mugwort will be achieved with applications of glufosinate, metsulfuron, triclopyr, or the dimethylamine salt and the isooctyl ester of 2,4-D, even at exceptionally high use rates.Nomenclature: Clopyralid; 2,4-D dimethylamine salt; dicamba; 2,4-D isooctyl ester; glufosinate; glyphosate; metsulfuron; pelargonic acid; picloram; triclopyr; mugwort, Artemisia vulgaris L. #3 ARTVU.Additional index words: Growth regulator herbicides, logarithmic sprayer, nonselective herbicides, perennial weed control, regrowth, rhizome.Abbreviations: MAT, month after treatment; YAT, year after treatment.