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Controlling Cool-Season Perennial Grassy Weeds in Turf

Spring is a great time to use postemergence herbicides on creeping bentgrass and quackgrass and to control tall fescue problems in desirable turfgrass.

Creeping bentgrass is a desirable turf, but it becomes a problem when it invades other cool-season turfgrasses. It forms dense patches and is characterized by soft, fine-textured (narrow), blue-green leaf blades and above-ground creeping stems called stolons.

The appearance and growth habits of quackgrass and tall fescue are much different than those of creeping bentgrass. Quackgrass has coarse-textured (wide) blue-green leaves with long, clawlike auricles (appendages where the leaf blade meets the stem). Quackgrass typically does not appear as distinct clumps in turf. It spreads by strong rhizomes, or horizontal underground stems. If you pull up quackgrass, the long white rhizomes will be visible. Quackgrass seeds and rhizomes will often find their way into lawn areas in agricultural soils.

The leaves of tall fescue are dark, emerald green, and coarse-textured. Tall fescue does not normally spread by above- or below-ground horizontal stems. It is apparent in lawns as clumps that grow more rapidly than the other lawn grasses it has invaded. It normally stands out several days after mowing because it grows taller and faster than the desirable species, resulting in a patchy appearance in most lawns.

Controlling these perennial grassy weeds is often difficult. One option is to pull or dig them out. Get as much of the roots as possible, including the stolons on creeping bentgrass and the rhizomes on quackgrass. Preemergence herbicides that prevent annual grasses such as crabgrass will not control these weeds.

No selective herbicides are available for creeping bentgrass and quackgrass, but the nonselective herbicide glyphosate (Roundup, Kleeraway) can be used to control these weeds and tall fescue as well. For the most effective control, apply herbicides when the weeds are green and actively growing. Glyphosate can damage or kill other actively growing plants it comes into contact with, so caution is advised. In the case of creeping bentgrass and quackgrass, be sure to spray an area large enough to include all of the creeping stems growing in the area; untreated stolons or rhizomes may continue to grow and develop into more unsightly weeds.

Chlorsulfuron (TFC) is a selective postemergence herbicide that can be applied to control actively growing tall fescue that has invaded Kentucky bluegrass. Chlorsulfuron often works slowly, causing the tall fescue to decline gradually rather than die quickly. It will kill or damage perennial ryegrass and may also cause yellowing or phytotoxicity to Kentucky bluegrass.

After the weeds have been removed or killed, the area needs to be replanted. Sod can be installed in the dead areas, or they can be reseeded. While the best time to reseed is late August and early September, the cool-season perennial grassy weeds may not be actively growing at that time.

Author: Tom Voigt Bruce Spangenberg


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