Responses of Imidazolinone-Resistant Corn, Several Weeds, and Two Rotational Crops to Trifloxysulfuron1

Field and greenhouse studies were conducted in 2000, 2001, and 2002 to evaluate the response of imidazolinone-resistant (IR) corn and selected weeds to trifloxysulfuron applied postemergence (POST). Treatments included a nontreated control and S-metolachlor applied preemergence at 1,075 g ai/ha followed by (fb) trifloxysulfuron POST at 0, 3.8, 7.5, 11.2, and 15 g ai/ha. IR corn visible injury was less than 6% from field applications of trifloxysulfuron. Visual symptoms were transient, and IR corn yield was not affected by trifloxysulfuron. Common ragweed, common lambsquarters, annual grass species (giant foxtail and large crabgrass), and carpetweed were controlled at least 95% by S-metolachlor fb trifloxysulfuron applications. Morningglory species (ivyleaf morningglory, pitted morningglory, and tall morningglory) were controlled at least 97% in 2000 and greater than 77% in 2001 from S-metolachlor fb trifloxysulfuron. Jimsonweed was not adequately controlled. S-metolachlor alone controlled annual grass species 90% but did not control the broadleaf weeds that were present. Wheat was planted following IR corn harvest, and non-IR corn was planted the following spring. No visible response was observed to rotational wheat or non-IR corn crops. Rotational non-IR corn yield was not affected by trifloxysulfuron and was not different from the yield of corn treated with S-metolachlor alone. In greenhouse studies, IR corn was injured 10% at 10 d after treatment with 380 g/ha trifloxysulfuron POST, but recovery was rapid. Based upon results, trifloxysulfuron may be used as an herbicide in IR corn, and rotational wheat and non-IR corn may be planted at normal intervals after cotton harvest. Nomenclature: Trifloxysulfuron; S-metolachlor; carpetweed, Mollugo verticillata (L.) #3 MOLVE; common lambsquarters, Chenopodium album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L # AMBEL; giant foxtail, Setaria faberi Herrm. # SETFA; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE; jimsonweed, Datura stramonium L. # DATST; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; pitted morningglory, I. lacunosa L. # IPOLA; tall morningglory, I. purpurea (L.) Roth # IPOPU; corn, Zea mays L. ‘Pioneer 32Z18 IR’, ‘Pioneer 33G26’; wheat, Triticum aestivum L. ‘Pocahontas’. Additional index words: Carryover, sulfonylurea. Abbreviations: ALS, acetolactate synthase enzyme (EC 4.1.3.18); DAT, days after postemergence treatment; fb, followed by; IR, imidazolinone-resistant; POST, postemergence; PRE, preemergence; WAP, weeks after planting.