ABSTRACT

Replicated field experiments were conducted at three locations in Louisiana during 1989-1992 to evaluate the use of Command herbicide for enhanced preemergence weed control on cotton safened with infurrow applications of Di-Syston or Thimet insecticide. Ten experiments were conducted over the course of the study. Except where otherwise noted, cotton treated with Command received an application of Di-Syston or Thimet 0.75 lb ai/A applied as an infurrow granule. Experiments were conducted on silt loam soils at the Northeast Research Station near St. Joseph, the Dean Lee Research Station near Alexandria, and the Whitter Farm near St. Francisville. Each of the soils contained approximately 1.0% organic matter. Soil pH at the St. Joseph and St. Francisville locations was approximately 6.0, and near 7.0 at the Alexandria site. Preemergence weed control varied greatly among herbicide treatments and environments. In general, Command at 0.75-1.0 lb ai/A preemergence surface (PES) provided greater control of wild poinsettia, spurred anoda, and cocklebur than did Cotoran 0.8-1.2 lb ai/A PES. Control of pitted and entireleaf morningglory, pigweed, and hemp sesbania was greater with Cotoran treatments.

Where moisture was marginal for activation of PES treatments, Command demonstrated greater herbicidal efficacy than Cotoran and much greater than Zorial. Command + Cotoran (0.75-1.0 + 0.8-1.2 lb ai/A) treatments tended to be more efficacious in control of morningglory, cocklebur, wild poinsettia, and spurred anoda than Cotoran alone. This effect was most apparent under marginal moisture conditions. Wild poinsettia was controlled >90% where Command was applied at 0.66-0.75 lb ai/A.

Cotton injury varied greatly with environment and in-furrow insecticide. Under light to moderate moisture conditions both Di-Syston and Thimet 0.75 lb ai/A adequately safened cotton from injury from Command 0.75-1.0 lb ai/A PES. Temik 0.5 lb ai/A did not protect cotton from Command injury. Under high rainfall conditions, neither Di-Syston nor Thimet adequately safened Command. The margin of safety for Command (0.75-1.0 lb ai/A ) + safener was much less than for Cotoran 0.8-1.2 lb ai/A. In two of the ten experiments reported, cotton was severely chlorotic and stands were significantly reduced in Command treatments, but not in Cotoran treatments. Cotton did recover from significant injury where stand losses were not prohibitive.