HERBICIDE TOLERANCE AND WEED-CONTROL IN SETHOXYDIM-TOLERANT CORN (ZEA-MAYS)

Homozygous, sethoxydim-tolerant corn was field tested at two locations in 1989 and 1990. Sethoxydim at 0.22, 0.44, and 0.88 kg ha-1 was appl ied to sethoxydim-tolerant corn in the 3- and 7-leaf stages. None of t he sethoxydim treatments caused visible injury to the sethoxydim-toler ant corn, but all treatments were lethal to a parental corn line used as a control. Sethoxydim applied at either stage of corn development h ad no effect on number of days to 50% silk emergence, plant height, or grain yield, compared to nontreated plants. Sethoxydim-tolerant corn was also tolerant to mixtures of sethoxydim plus other postemergence h erbicides that control dicotyledonous weeds. Sethoxydim mixed with atr azine or sethoxydim applied in sequential applications with dicamba or 2,4-D gave annual grass control similar to sethoxydim applied alone. However, the sethoxydim plus bentazon treatment resulted in reduced gr ass control in comparison to sethoxydim alone. When the broadleaf herb icides were mixed with sethoxydim or applied as sequential treatments, broadleaf weed control was the same as when the broadleaf herbicides were applied alone. The high level of corn tolerance to sethoxydim and the broad spectrum of weed control resulting from combinations of set hoxydim plus other postemergence herbicides indicates that sethoxydim- tolerant corn hybrids could increase the options available for weed co ntrol in corn.