Imazethapyr-based weed control treatments were evaluated in water-seeded imidazolinone-resistant (IR) rice in Louisiana in 2000 and 2001. Treatments included imazethapyr applied to soil before seedling flood (surface [SURF] applied) or no soil application (no SURF), followed by imazethapyr applied postemergence (POST). Averaged over SURF application treatments (SURF, no SURF), all imazethapyr mixtures increased control of barnyardgrass at 14 and 42 d after POST treatment (DAT) compared with imazethapyr alone. Treatments containing imazethapyr-applied SURF followed by POST treatments controlled red rice 90 to 96% at 21 DAT. Alligatorweed and hemp sesbania control increased with POST mixtures compared with imazethapyr-only treatments at 35 DAT. Rice yield increased with imazethapyr applied SURF compared with no SURF application, averaged over POST applications. Other herbicides will be required to control troublesome weeds such as hemp sesbania and alligatorweed in an IR rice production system.

The efficacy of imazethapyr in drill-seeded imidazolinone-resistant rice was evaluated in Louisiana in 2000 and 2001. Imazethapyr was applied preemergence (PRE), or no PRE, followed by a postemergence (POST) application of imazethapyr alone, or in a mixture with bensulfuron, bentazon plus aciflurofen, carfentrazone, halosulfuron, propanil plus molinate, triclopyr, or V-10029. Imazethapyr applied PRE followed by a POST application of imazethapyr controlled barnyardgrass equivalent to or higher than other treatments evaluated. Red rice control at 35 days after postemergence treatment (DAT) was 66 to 81% with imazethapyr applied PRE followed by any POST application, but a reduction in control was observed with a POST application of imazethapyr. Although alligatorweed control increased with POST applications, these treatments suggested only suppression. Hemp sesbania control never exceeded 10% with imazethapyr-only treatments and at 35 DAT, all POST applications, except bensulfuron, increased control above 84%. Rice yield increased with treatments receiving a PRE application of imazethapyr compared with no imazethapyr applied PRE.

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.