Herbicidal Control of Common Milkweed (Asclepias syriaca)

Abstract

Five field experiments were conducted to evaluate effectiveness of postemergence herbicidal treatments. Amitrole (3-amino-s-triazole) at 1.1 kg ai/ha and picloram (4-amino-3,5,6-trichloropicolinic acid) at 0.6 kg ai/ha reduced stands of common milkweed (Asclepias syriaca L.) for a 4-yr period. Glyphosate [N-(phosphonomethyl)glycine] at 2.2 kg ai/ha reduced stands of milkweed for two to three growing seasons. Glyphosate or amitrole applied in June (early bud stage) more effectively reduced milkweed stands in the second year than did the herbicides when applied in August (post-flowering stage). Treatments of 2,4-D [(2,4-dichlorophenoxy)acetic acid], 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and dicamba (3,6-dichloro-o-anisic acid) did not reduce stands of common milkweed.