CONTROL OF TRIAZINE-RESISTANT KOCHIA (KOCHIA-SCOPARIA) IN CONSERVATION TILLAGE CORN (ZEA-MAYS)

Triazine-resistant (TR) kochia control with herbicides was evaluated in the greenhouse and in the field on ridge-till and ecofallow corn. In the greenhouse, bromoxynil, dicamba, linuron, and paraquat applied POST controlled TR kochia > 86%. Control of TR kochia with 2,4-D ester at 0.3 kg ae ha-1 varied with kochia biotype. In three ridge-till fields in 1985, atrazine plus florochloridone at 2.2 plus 0.6 kg ai ha-1 applied before planting plus a layby cultivation was the only treatment that reduced TR kochia biomass to < 750 kg ha-1. In 1986, atrazine plus dicamba at 2.2 plus 0.3 kg ha-1, atrazine plus fluorochloridone at 2.2 plus 0.3 or 0.6 kg ha-1 applied EPOST; atrazine at 2.2 kg ha-1 applied EPOST followed by an MPOST application of bromoxynil at 0.3 or 0.4 kg ha-1, or dicamba plus 2,4-D ester at 0.3 plus 0.3 kg ha-1; and an MPOST application of atrazine plus dicamba at 1.3 plus 0.5 kg ha-1, atrazine plus pyridate at 1.1 plus 1.0 kg ai ha-1, or pyridate plus cyanazine at 1.0 plus 1.7 kg ai ha-1 followed by a layby cultivation reduced kochia biomass to < 400 kg ha-1. In ecofallow corn, the only herbicide treatment that consistently controlled TR kochia > 95% 21 to 30 d after application was pyridate plus fluorochloridone at 1.0 plus 0.6 kg ha-1. Other treatments were less effective because kochia was too large or additional kochia emerged after application. When added to atrazine plus cyanazine, paraquat at 0.3 kg ai ha-1 plus dicamba was more effective than paraquat plus 2,4-D ester or paraquat alone in controlling TR kochia.