Comparison of herbicide programs in imidazolinone tolerant corn

Field studies were conducted in 1998 at Jackson, Milan, Knoxville, and Spring Hill, Tennessee, to examine several herbicide programs for weed control in imidazolinone-tolerant corn. Field corn variety FFR 797 IMI was no-till or minimum-till planted at all locations. The treatments were replicated four times in a randomized block design. Treatments ranging from a PRE-only to PRE followed by postemergent (POST) to total POST applied to examine weed control, crop injury, and yield. Crop oil concentrate (COC) was combined with atrazine when applied POST, while nonionic surfactant was added to all other POST treatments. Visual evaluations were taken four weeks after treatment to evaluate control of broadleaf signalgrass (Brachiaria platyphylla (Griseb.) Nash), large crabgrass (Digitaria sanguinalis (L.) Scop), Palmer amaranth (Amaranthus palmeri (S.) Wats), pitted morningglory (Ipomoea lacunosa L.), and sicklepod (Senna obtusifolia (L.) Irwin and Barnaby). None of the treatments controlled sicklepod at Milan due to high population density (600-5000 plants/m²). Imazethapyr + imazapyr + dicamba POST and atrazine + metolachlor PRE followed by prosulfuron + primisulfuron + nicosulfuron POST controlled these weeds while imazethapyr + imazapyr POST, imazethapyr + imazapyr + pendimethalin POST, and atrazine + metolachlor PRE followed by flumetsulam + clopyralid + nicosulfuron POST controlled all weeds >86% except Palmer amaranth (<67%). Imazethapyr + imazapyr + nicosulfuron POST failed to control Palmer amaranth and only controlled sicklepod 75% at Spring Hill. Atrazine + metolachlor PRE followed by nicosulfuron POST did not control Palmer amaranth and pitted morningglory but controlled all other weeds. Atrazine + metolachlor PRE followed by dicamba POST failed to control broadleaf signalgrass and pitted morningglory, but controlled large crabgrass, Palmer amaranth, and sicklepod. Imazethapyr + imazapyr + atrazine POST controlled all weeds except pitted morningglory (71%), while atrazine + crop oil concentrate controlled the dicot weeds but had little monocot activity. Nicosulfuron + rimsulfuron + atrazine POST controlled broadleaf signalgrass and Palmer amaranth, but only partially controlled pitted morningglory control. Sicklepod was controlled at Knoxville but not at Spring Hill by the mixture of these three herbicides. Although atrazine + metolachlor PRE controlled broadleaf signalgrass and sicklepod at Knoxville, the treatment did not control all other weeds at Jackson and Spring Hill. Corn yields were reduced at Milan from sicklepod competition. Yields were also low for treatments that did not provide adequate large crabgrass and Palmer amaranth control. Slight corn injury was observed but did not appear to influence corn yields.