Vol. 54—2000 - NorthEastern Weed Science Society

MANAGING FENOXAPROP
RESIST ANT CRABGRASS IN GOLF COURSE TURF
D.R. Spak'
ABSTRACT
Herbicide resistance management has recently become an important consideration in
managing turf grass weeds, particularly annual grassy weeds. The reliance on a limited number of
herbicides representing only a few herbicide classes has lead to the development of isolated cases
of resistance in weeds such as crabgrass (Digitaria ischaemum), goosegrass (Eleusine indica),
and annual bluegrass (Poa annua L.).
Fenoxaprop was first registered in 1985 for postemergence control of smooth crabgrass in
cool season turfgrasses. In 1996, the first documented case of crabgrass resistance to fenoxaprop
occurred on a golf course tee where fenoxaprop had been used exclusively for more than 12
years. Because no other effective postemergent option was available in creeping bentgrass
(Agrostis palustris), no other crabgrass or goosegrass herbicides were used during this time.
There is a need to develop herbicide resistance management strategies (cultural and chemical) for
preventing the development of resistance in summer annual grasses namely crabgrass and
goosegrass. In addition, there is also the need to develop strategies to prevent the spread of
resistant grasses once resistance has developed.
In 1999, a study was initiated on a golf course tee where fenoxaprop resistance was
suspected due to the gradual loss in crabgrass control. The objective was to evaluate various
herbicide programs for the controlling both crabgrass and goosegrass. Herbicide treatment
programs included the use of tank-mixing preemergence andlor postemergence herbicides with
different modes of action. The companion herbicides included bensulide, dithiopyr, and the newly
registered herbicide quinclorac, each applied alone or in combination with fenoxaprop early (pre
to spike) or mid-postemergence (1-2 tiller).
Results of this study will be discussed and perspectives on managing and preventing
resistance to fenoxaprop and other herbicides will be presented.
I Field Development Manager, AgrEvo USA Company, Cochranville, PA 19330
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