Field trials were conducted in 2000, 2001, and 2002 at Tifton, GA, and Plains, GA, to evaluate the effects of simulated imazapic residues on cotton growth and yield. Preemergence applications of imazapic at 1, 2, 5, 9, 18, and 36 g ai/ha were made to four different cotton varieties (two at each location) and included a nontreated control. There were no differences in cotton variety response to imazapic. Each cotton variety responded to imazapic in a similar manner. Analysis of cotton yield as a percentage relative to the nontreated control indicated no difference in variety for location, so data for varieties were combined. At Tifton, cotton injury was exponentially related to imazapic rate with a maximum injury of 44% for 35 g/ha. Seed cotton yields at this location were reduced 0, 6, 6, 14, 16, 34, and 61% at 1, 2, 5, 9, 18, and 36 g/ha, respectively. For Plains, cotton exhibited extreme sensitivity with injury exceeding 70% for imazapic at 5 g/ha and greater than 95% for 18 g/ha. Seed cotton yields at this location were reduced 60% or more from imazapic rates of 5 g/ha and greater. These results indicated that soil type is a key factor in the response of cotton to imazapic.

Nomenclature: Imazapic; cotton, Gossypium hirsutum L.

Additional index words: Carryover injury, herbicide persistence, residual herbicide, simulated carryover.

Abbreviations: CEC, cation-exchange capacity; DAT, days after treatment.