Weed Control in Field Corn (Zea mays) with RPA 201772 Combinations with Atrazine and S-Metolachlor1

Abstract

The premix atrazine 1 S-metolachlor is commonly used to control a wide range of weeds in corn, but it is weak on velvetleaf and several other broadleaf species. RPA 201772, used at reduced rates in combination with atrazine 1 S-metolachlor, may improve the weed control spectrum. In field studies at Urbana and Dekalb in 1998 and 1999, RPA 201772 was combined with a premix of atrazine at 1,820 g ai/ha and S-metolachlor at 1,408 g ai/ha to compare RPA 201772 rate effects on corn injury, weed control, and yield. RPA 201772 was applied at 0, 26, 53, 78, 105, and 132 g ai/ ha early preplant (EPP), preplant incorporated (PPI), and preemergence (PRE). Compared with at- razine 1 S-metolachlor alone, RPA 201772 combinations did not improve giant foxtail control. However, RPA 201772 at 26 or 53 g/ha increased control of redroot pigweed, common lambsquarters, ivyleaf morningglory, common ragweed, giant ragweed, and velvetleaf in some environments. At Urbana in both years, RPA 201772 at 26 g/ha in combination with atrazine 1 S-metolachlor increased velvetleaf control 15% compared with the premix alone. RPA 201722 at 26 to 78 g/ha decreased velvetleaf densities with all application methods. Greater weed control and higher corn yield occurred in treatments applied PRE or PPI compared with EPP applications, except where conditions were dry after PRE applications. This research demonstrates the benefit of RPA 201772 at low rates for broadleaf weed control with less potential for crop injury compared with high RPA 201772 rates. Nomenclature: RPA 201772 (proposed common name, isoxaflutole), 5-cyclopropyl isoxazol-4-yl-2- mesyl-4-trifluoromethylphenyl ketone; common lambsquarters, Chenopodium albumL. # 3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; giant foxtail, Setaria faberi Herrm. # SETFA; giant ragweed, Ambrosia trifidaL. # AMBTR; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; redroot pigweed, Amaranthus retroflexus L. # AMARE; velvetleaf, Abutilon theophrasti Medicus # ABUTH; corn, Zea mays L. Additional index words: HPPD inhibitor, isoxaflutole, reduced herbicide rates. Abbreviations: DAE, days after emergence; DAT, days after treatment; EPP, early preplant; PPI, preplant incorporated; PRE, preemergence.