Auxin-type herbicides such as 2,4-D and dicamba are commonly used to control kochia in small grain production areas, but poor kochia control with these herbicides has been reported. Several auxinic herbicide-resistant kochia inbreds were evaluated for their response to 2,4-D or dicamba and to alternative herbicide treatments. Values of the dose of the herbicide causing 50% visible injury to test plants (I₅₀) from week 1 to week 4 after treatment with 2,4-D were unchanged for six of the seven 2,4-D–resistant inbreds, indicating that these plants may recover to produce seeds. In contrast, the corresponding I₅₀ values for dicamba decreased for five of the six dicamba-resistant inbreds, indicating that kochia was not recovering from the treatment. Postemergence treatments with atrazine, carfentrazone, fluroxypyr, bromoxynil plus MCPA, nicosulfuron plus dicamba, and nicosulfuron plus dicamba plus atrazine, all provided adequate to excellent control of resistant kochia inbreds. Alternative chemical control options are available for managing auxinic herbicide-resistance in kochia.

Nomenclature: Atrazine; bromoxynil; carfentrazone; 2,4-D; dicamba; fluroxypyr; MCPA; nicosulfuron; kochia, Kochia scoparia (L.) Schrad. #³ KOCSC.

Additional index words: Herbicide resistance.

Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); dma, dimethylamine; I₅₀, dose of the herbicide causing 50% visible injury to test plants; WAT, weeks after treatment.