Abstract: Field experiments were conducted in 1997 and 1998 near Columbia and Novelty, MO, and at Urbana, IL, to evaluate corn injury, weed control, corn yield, and estimated economic returns with weed management programs in glufosinate-resistant corn. Herbicide programs included acetochlor preemergence (PRE) followed by glufosinate alone or with atrazine postemergence (POST) and total POST programs consisting of single and sequential applications of glufosinate alone or tank mixed with acetochlor, atrazine, or acetochlor plus atrazine. Metolachlor PRE followed by dicamba plus atrazine early POST (EPOST) and metolachlor plus atrazine PRE were included for comparison. In the total POST treatments, mid-POST applications controlled shattercane and common cocklebur better than EPOST applications. However, yield reductions as high as 23% occurred because of early-season weed interference, although weeds were controlled later in the season. Applying atrazine with glufosinate generally increased control of giant foxtail, common cocklebur, morningglory species, and common waterhemp compared to glufosinate alone, but did not increase control of common lambsquarters, velvetleaf, or Pennsylvania smartweed. Corn yield was positively correlated with weed control (r = 0.88) and more strongly dependent on grass (r = 0.82) than broadleaf (r = 0.70) weed control. Net incomes were positively correlated to corn yield (r = 0.73). Four of the top six net income-producing treatments included two herbicide applications. Three of the treatments were PRE followed by POST programs, and the fourth was a sequential POST treatment of glufosinate.
Nomenclature: Acetochlor; atrazine; dicamba; glufosinate; metolachlor; common cocklebur, Xanthium strumarium L. #3 XANST; common lambsquarters, Chenopodium album L. # CHEAL; common waterhemp, Amaranthus rudis Sauer # AMATA; giant foxtail, Setaria faberi (L.) Herrm. # SETFA; morningglory, Ipomoea spp.; Pennsylvania smartweed, Polygonum pensylvanicum L. # POLPY; shattercane, Sorghum bicolor (L.) Moench. # SORVU; velvetleaf, Abutilon theophrasti (L.) Medikus # ABUTH; corn, Zea mays L. # ZEAMX ‘Pioneer 34A55’.
Additional index words: Corn yield, economic returns, glufosinate-resistant crop, AMATA, ABUTH, CHEAL, POLPY, SETFA, SORVU, XANST, ZEAMX.
Abbreviations: ALS, acetolactate synthase; CV, coefficient of variation; EPOST, early postemergence; MPOST, mid-postemergence; POST, postemergence; PRE, preemergence; WAT, weeks after treatment.