"Staple" Herbicide (Pyrithiobac Sodium) recently received Federal registration for postemergence weed control in cotton. Since 1990, more than 100 replicated small plot trials have been conducted in West Texas and New Mexico to evaluate preemergence and postemergence efficacy on key weeds in cotton, crop tolerance, and grass herbicide interactions. This paper summarizes these test results.

Postemergence applications of Staple at 1.0 oz ai/ac have given good to excellent (>80%) control of Palmer amaranth, redroot pigweed, prairie sunflower, red morningglory, entireleaf morningglory, devil's claw, lanceleaf sage and common cocklebur. Control of venice mallow has been poor at 27%. Crop injury from postemergence applications of Staple 1.0 oz ai/ac has averaged 5.0% at 7 to 14 days and decreased to 1.1% at 21 to 28 days after treatment.

Strong antagonism in johnsongrass control has been seen when Staple is tank mixed with most over-the-top grass herbicides. Control of seedling and rhizome johnsongrass was decreased when Staple was mixed with Select, Fusilade and Poast Plus. The addition of Staple to "Assure" II had no effect on grass control.

Preemergence trials have concentrated on Staple at 0.5 to 1.0 oz ai/ac alone and in combination with "Karmex" Herbicide. Staple at 0.5 to 1.0 oz ai/ac provided good to excellent (>80%) control of palmer amaranth, lanceleaf sage and venice mallow, while control of red morningglory and entireleaf morningglory required Staple at 1.0 oz ai/ac. The addition of Karmex 8.0 and 12.8 oz ai/ac to Staple increased control over Staple alone on red morningglory, prairie sunflower and devil's claw. Crop injury in sandy loam to clay soils following treatment from Staple 1.0 oz ai/ac averaged 1.1% at 14 days and 2.4% at 28 days after treatment. Crop injury in sand to loamy sand soils averaged 14.4% at 14 days after treatment and increased to 26.8% at 28 days after treatment.