Control and regrowth of hemp dogbane, wild blackberry, and triazine-resistant common lambsquarters (TR-CHEAL) were studied in no-till corn from 1992 to 1994. Hemp dogbane, wild blackberry, and TR-CHEAL population increased 10, 123, and 177%, respectively, between 1992 and 1994 in plots treated with PRE applications of paraquat, atrazine, and metolachlor (weedy checks). POST applications of tank mixtures of 35 g ai/ha nicosulfuron or 20 g/ha primisulfuron with 280 g/ha 2,4-D or 140 g/ha dicamba, and 560 g/ha dicamba applied alone controlled hemp dogbane, wild blackberry, and TR-CHEAL 67 to 98%. These treatments reduced the population or prevented expansion of these weeds the year following treatment. In 1992, corn yield response to weed control was inconsistent. In 1993 and 1994, all plots treated with POST herbicides yielded higher than the weedy check. Corn yield of plots treated with combinations of nicosulfuron or primisulfuron with 2,4-D or dicamba and 560 g/ha dicamba applied alone were 102 to 149% and 124 to 153% higher than the weedy check in 1993 and 1994, respectively.

Hemp dogbane and wild blackberry have become significant weed problems in no-tillage corn production in Maryland. Nicosulfuron (31 to 62 g ha−1) plus crop oil concentrate (COC) gave 67% or more hemp dogbane and wild blackberry control. There was no difference in hemp dogbane or wild blackberry control between 31 and 94 g ai ha−1 nicosulfuron. Tank mixtures of 2,4-D or dicamba with nicosulfuron gave 72 to 100% hemp dogbane and wild blackberry control. Hemp dogbane control following applications of 560 g ha−1 2,4-D was 97% in 1989 and 63% in 1990. Wild blackberry control with 2,4-D was 40% both years. Dicamba at 280 g ha−1 gave 70 and 55% control of hemp dogbane and 75 and 65% control of wild blackberry in 1989 and 1990, respectively. Triclopyr plus 2,4-D provided 72 to 98% hemp dogbane control and 92 to 98% wild blackberry control. However, triclopyr plus 2,4-D applied at 280 plus 560 g ha−1 injured corn, and corn yields were reduced compared with weedy controls in 1990.