A field experiment was conducted in 1989 to determine the effect of application timing and of serial applications of Fusilade^® (fluazifop-P) applied postemergence to cotton (Gossypium hirsutum L. 'DES 119') and bermudagrass (Cynodon dactylon L.). Fusilade was applied broadcast to cotton in the cotyledon stage with bermudagrass runners 4 to 6 inches long (early) and/or to cotton 5 to 8 inches tall with bermudagrass runners 18 to 24 inches long (late). The herbicide was applied in water at 20 gallons per acre containing 1.25% v/v crop oil [polyoxyethylene sorbitan fatty acid ester:mineral oil (17:83% w/w)]. Applications were made either early, late, or both at either one-half the recommended rate at 0.094 and/or at the recommended rate of 0.188 lb ai/A. The experimental area was located on a silt loam soil (Mollic Hapludalf) in established bermudagrass. The experimental design was a randomized complete block of four-row plots, 40 ft long with rows spaced 40 inches apart. Each treatment was replicated four times. Significance was determined at the 95% level using Duncan's multiple range test. Cotton yield was determined from the middle two rows of each plot using a mechanical harvester.

The highest yields of seed cotton (985 to 1320 lb/A) occurred in treatments where Fusilade was applied early at the recommended rate and as serial applications at all rate combinations. Yield was not significantly increased when serial application rates exceeded the recommended rate. Neither the half rate applied early nor the half or the recommended rate applied late resulted in yields significantly greater than the untreated control (655 to 831 lb/A).

Bermudagrass control at 6 weeks after the first application was greatest (>99%) with each treatment where Fusilade was applied in serial applications. Excellent weed control (93%) was also obtained when Fusilade was applied early in one application at the recommended rate. Moderate bermudagrass control (80%) was obtained with the recommended rate applied late. The least bermudagrass control (<75%) was obtained with Fusilade applied in one application at the half rate either early or late.

In conclusion, Fusilade applied at the recommended rate early when cotton was in the cotyledon stage was as effective for increasing cotton yield as serial applications at the half rate, the recommended rate, or combinations of the recommended and half rate. Results also indicate that when bermudagrass control is delayed for 3 to 4 weeks after cotton emergence, cotton yield can be decreased even though moderate to excellent bermudagrass control can be obtained.