Confirmation and Management of Common Ragweed (Ambrosia artemisiifolia) Resistant to Diclosulam

Selection for biotypes of common ragweed expressing resistance to acetolactate synthase (ALS)–inhibiting herbicides has increased in North Carolina and surrounding states. Research was conducted in North Carolina to confirm common ragweed resistance to diclosulam and to compare herbicide programs designed to control ALS-resistant common ragweed in corn, cotton, peanut, and soybean. In greenhouse experiments, 50% inhibition values following POST application of diclosulam for mortality of plants, visual estimates for percentage of control, and percentage of reduction in plant fresh weight were 557- to 653-fold higher for the suspected ALS-resistant biotype compared with a suspected ALS-susceptible biotype. Herbicides with different modes of action, including atrazine, dicamba, and glyphosate in corn; fomesafen, glyphosate, MSMA, and prometryn in cotton; bentazon, flumioxazin, and lactofen in peanut; and flumioxazin, glyphosate, and lactofen in soybean controlled common ragweed more effectively than programs relying on cloransulam-methyl (soybean), diclosulam (peanut), thifensulfuron (corn), and trifloxysulfuron (cotton), which typically control nonresistant common ragweed populations. Applying tank-mix or sequential applications of herbicides with different modes of action was effective in controlling ALS-resistant common ragweed in all crops.