Annual bluegrass, orPoa annua, is a common weed on Florida golf courses during the winter play season and has been a topic of discussion on recent TAS visits. Annual bluegrass is genetically diverse with biotypes ranging from true annuals (die out every year) to those that are much more perennial (survive from year to year). The annual types produce an abundance of seeds over an extended period of time. This combination of genetic diversity and indefinite seeding period makes chemical control difficult.
Annual bluegrass produces good turf quality in other regions where the perennial varieties often dominate the putting surface. Unfortunately, the annual bluegrass that shows up in Florida putting greens is the weaker, annual variety. The prolific seedhead production causes unsightly conditions. Worse, the high heat and humidity that occurs in late spring makes the plant prone to disease.
If left untreated, annual bluegrass can proliferate throughout the golf course, disrupting golf course aesthetics and playability. When there are only a few annual bluegrass plants in a green physical removal can be effective. However, large populations, and areas on tees, fairways and roughs are generally treated with herbicides. There are a variety of chemicals used to manage emerging annual bluegrass seedlings (pre-emergence) as well as those that selectively control mature plants (post-emergence) in warm-season turf. For a current list of registered chemicals for Florida golf courses, refer to the University of Florida’sPest Control Guide for Turfgrass Managers. Annual bluegrass plants that escape pre-emergence control can be treated with a post-emergence herbicide to maintain uniform turf quality.
Much of the annual bluegrass in our region is in an immature state and is more sensitive to herbicide treatments at this time. As such, improved annual bluegrass management will occur if post-emergence treatments are applied sooner rather than later. As the plant matures, it hardens off and becomes less sensitive to chemical treatments. Also, postponing herbicide applications perpetuates weed populations, as it allows annual bluegrass plantlets to produce more seeds that emerge in subsequent years.
Source: Todd Lowe, tlowe@usga.org or 941-828-2625