Greenhouse studies verified that smooth crabgrass from a golf course tee in southern New Jersey was resistant to fenoxaprop-P, although smooth crabgrass from a nearby untreated rough was susceptible to this herbicide. Fenoxaprop-P-resistant plants were injured, however, when fenoxaprop-P was applied at levels above the maximum use rate for turf. Fenoxaprop-P applied postemergence at 0.76 kg ai/ha, four times the maximum rate, reduced shoot weight of the resistant biotype by 35%, whereas application of 1.52 kg/ha, eight times the maximum rate, reduced shoot weight by 64%. Large crabgrass and the susceptible biotype of smooth crabgrass were controlled by fenoxaprop-P applied at 0.1 kg/ha. Fenoxaprop-susceptible and -resistant biotypes of smooth crabgrass had a similar response to MSMA, dithiopyr, and quinclorac applied postemergence. The fenoxaprop-P–resistant smooth crabgrass biotype was controlled by the cyclohexanedione herbicides sethoxydim and clethodim, but the aryloxyphenoxypropionate herbicides fluazifop and quizalofop reduced shoot weight by only 15 to 66% depending on herbicide and rate.
Nomenclature: Clethodim; dithiopyr; fenoxaprop-P; fluazifop-P; MSMA; quinclorac; quizalofop; sethoxydim; large crabgrass, Digitaria sanguinalis (L.) Scop. #3 DIGSA; smooth crabgrass, Digitaria ischaemum Schreb. Ex Muhl # DIGSU.
Additional index words: Herbicide resistance, postemergence grass herbicides, turfgrass.
Abbreviations: ACCase, acetyl-coenzyme A carboxylase; APP, aryloxyphenoxypropionate; CHD, cyclohexanedione; smooth crabgrass (R), fenoxaprop-P–resistant smooth crabgrass; smooth crabgrass (S), fenoxaprop-P–susceptible smooth crabgrass; WAT, weeks after treatment.
