TURF TIPS CONTROLLING WINTER WEEDS, PART 1 – Annual Bluegrass By Jim Brosnan, Ph.D., Greg Breeden, and T.J. Samples, Ph.D., The University of Tennessee nnual bluegrass (Poa annua) is a problematic winter weed that commonly invades all types of turf (golf courses, home lawns, sports fields, etc.) regardless of mowing height or frequency. Despite the persistence of this weed species, certain steps can be taken to provide effective control this winter.
as the calendar quickly approaches December, it can be easily concluded that preemergence control is not an option for 2009.
Identification
Selective herbicides
The most important step in controlling any weed is proper identification. It is impossible to know how to control a weed without knowing what weed it is that you are trying to eradicate. Certain characteristics help identify annual bluegrass. The leaf blade is folded in vernation, has a boat-shaped tip and may appear to be rippled or slightly wrinkled (Photo 1). Annual bluegrass plants possess a long, membranous, slightly pointed ligule, and they produce panicle-type seedheads that are triangular in shape with spikelets bunched toward the ends (Photo 2). These seedheads start to emerge in the spring, and viable seed can be produced in just a few days after pollination. This feature is one of the reasons that annual bluegrass infestations are so widespread.
Numerous options are available for selective control of annual bluegrass in bermudagrass (Cynodon spp.) and zoysiagrass (Zoysia spp.) turf. Sulfonylurea herbicides like Revolver (foramsulfuron) and Monument (trifloxysulfuron-sodium) effectively control annual bluegrass in both dormant and actively growing bermudagrass and zoysiagrass. Both products are labeled for use by professional applicators on golf courses, sports fields, and residential and commercial lawns. Princep (simazine) and Aatrex (atrazine) are two herbicides that exhibit pre- and postemergence activity against annual bluegrass in various warm-season grasses. However, seeding into areas treated with these herbicides must be delayed for four to six months after treatment. These herbicides, especially Aatrex, can injure bermudagrass. None of the products above are labeled for use on putting greens. Several selective herbicides are labeled for postemergence control of annual bluegrass in cool-season turf. Prograss (ethofumesate) is labeled for annual bluegrass control in Kentucky bluegrass (Poa pratensis), perennial ryegrass (Lolium perenne), creeping bentgrass (Agrostis stolonifera) and tall fescue (Festuca arundinacea) turf. Two sequential applications are required, with the first applied in mid-November and the second applied three weeks later. The product has been referred to as the “holiday herbicide,”
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Preemergence control Annual bluegrass can be effectively controlled with timely applications of preemergence herbicides. The same products used for control of crabgrass (Digitaria spp) can be used to control annual bluegrass preemergently. In order to be effective, however, these herbicides should be applied prior to the germination of annual bluegrass seed. Annual bluegrass seed germinates once soil temperatures fall below 70ºF, and germination continues for the next two to three months. In East Tennessee, germination may begin as early as late August. That being said, 18
TENNESSEE TURFGRASS
Postemergence control Annual bluegrass can be effectively controlled with both selective and non-selective postemergence herbicides.
as effective results have been reported with applications made near Thanksgiving and Christmas. Spring applications of Prograss to overseeded bermudagrass stands often delay spring green-up. Velocity (bispyribac-sodium) provides effective control of annual bluegrass in perennial ryegrass and creeping bentgrass golf course fairways only. Preferred programs involve sequential applications in the spring of the year when air temperatures exceed 55ºF.
Non-selective herbicides Non-selective herbicides like Roundup Pro (glyphosate) and Finale (glufosinate) can be used to control annual bluegrass in dormant bermudagrass stands. These treatments are not recommended on zoysiagrass, as this species may not go completely dormant in the transition zone. In order to be effective, these herbicides must be applied when annual bluegrass plants are actively growing. Target your treatments for days when air temperatures are greater than 45ºF – 50ºF. Two major advantages to non-selective herbicide applications are that (1) they are more economical than their selective counterparts and (2) they control a broad spectrum of weeds in addition to annual bluegrass. Winter annual broadleaf weeds that often cause problems during the winter, like henbit (Lamium aplexicaule) and common chickweed (Stellaria media), can be controlled with applications of non-selective herbicides. Strategies for controlling winter annual broadleaf weeds will be addressed in the next issue of Tennessee Turfgrass. For more information on controlling other turf weeds in Tennessee, visit the University of Tennessee’s turfgrass weed science website, http://tennesseeturfgrassweeds.org.
OCTOBER/NOVEMBER 2009 Email TTA at: tnturfgrassassn@aol.com