Factors Influencing Fenoxaprop Efficacy in Cool-Season Turfgrass

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Abstract
Experiments were conducted in Massachusetts and New York to evaluate the potential influence of plant growth stage, spray volume, nozzle type, additional surfactant, and herbicide formulation on smooth and large crabgrass control in turf with fenoxaprop. At a well-watered site, crabgrass control with fenoxaprop was equal to or greater than with MSMA. On an irrigated, fertilized site, crabgrass growth stage did not influence fenoxaprop efficacy. Excellent control of up to 5-tiller smooth crabgrass was obtained with 0.20 kg/ha of fenoxaprop. On nonirrigated turf, fenoxaprop was less effective on tillered crabgrass than on 2- to 5-leaf weeds. Under very dry conditions, fenoxaprop was ineffective regardless of growth stage. Control with MSMA was less affected by drought than was fenoxaprop. Spray volumes, between 140 and 1120 L/ha, did not affect fenoxaprop efficacy; however, high volume applications (1120 L/ha) with floodjet nozzles were less effective than flat fan nozzle treatments in two of three tests. Added surfactant did not improve efficacy except with floodjet nozzles on a droughty site. No differences were observed between the water-based and the emulsifiable concentrate formulations of fenoxaprop. Fenoxaprop caused temporary phytotoxicity (≤20% reduction in turf quality) to established Kentucky bluegrass and perennial ryegrass.