Field Bindweed Control with Dicamba and 2,4-D, and Crop Response to Chemical Residues

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Abstract
Under furrow irrigation, control of field bindweed (Convolvulus arvensisL.) was at least 90% where 4.5 and 6.7 kg/ha of 3,6-dichloro-o-anisic acid (dicamba) had been applied 1 year before. Dicamba at 2.2 kg/ha, mixtures of dicamba and (2,4-dichlorophenoxy)acetic acid (2,4-D), and 2,4-D alone were less effective. No herbicide treatment had eradicated field bindweed after 3 years, but the combined use of herbicides, tillage, and crop competition had suppressed the growth of field bindweed by 31 to 55%. Sugarbeet (Beta vulgarisL.) seedlings appeared normal where 2,4-D had been applied 8 months earlier, but over 90% of the seedlings were killed in plots treated with dicamba. Treatment with 2.2 kg/ha of 2,4-D and dicamba, singly or in combination, resulted in yields of grain sorghum (Sorghum bicolor(L.) Moench) significantly greater than yields from the untreated field bindweed check. The 4.5 and 6.7-kg/ha rates of dicamba still affected sugarbeets during the second year following treatment. Corn (Zea maysL.) production was not affected in the third year by any herbicide treatment. Dicamba, applied at 2.2, 4.5, and 6.7 kg/ha, persisted in the upper 15 cm of top soil for at least 12 months in amounts that were phytotoxic to field beans (Phaseolus vulgarisL.) and sugarbeets.