University of Illinois Extension
Bruce Spangeberg

These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area.

Stateline Yard & Garden

Perennial Grass Weeds in Lawns

March 12, 1998

With mild weather and a lack of snow for several weeks, lawns and landscape plantings have been easy to inspect. Although the weather may fluctuate between winter and early spring over the next few weeks, a common observation will be greening patches of coarse, weedy grasses in the lawn. Oftentimes these plants may be mistakenly identified as crabgrass.

Crabgrass is a warm season annual, and all the crabgrass plants from the 1997 season are dead. In order to return in 1998, crabgrass would need to sprout from seeds. This will not happen until soil temperatures reach 60 degrees and stay there, probably not until late May or early June.

So what are the greening, coarse grasses present in lawns? Most likely they are perennial species, such as tall fescue or quackgrass. Tall fescue has wide leaf blades and will grow in very distinct clumps, making a very patchy appearance in Kentucky bluegrass lawns

Quackgrass is similar in appearance. One major difference is the presence of strong rhizomes—horizontal underground stems. If you go to pull-up quackgrass, this long rhizome, or runner, will be visible. In addition, quackgrass has long, claw-like auricles—appendages near where the leaf blade meets the stem.

Controlling either of these grassy weeds is difficult. The preemergence herbicides used to prevent crabgrass do not get these weeds out of a lawn. One option is to pull or dig them out. Get as much of the roots as possible, and for quackgrass, also get the rhizome.

Another option is to use the herbicide glyphosate ( Roundup, Kleeraway) on these weeds. Wait until they are fully green and actively growing to get good control. Any desirable lawn grasses, however, will also be killed or damaged, so be sure to direct spray to the weeds and keep contact to the lawn grasses to a minimum.

After the weeds have been removed or killed, the area needs to be reseeded. Given a choice, the best time to reseed is late August into early September. For this reason, it may be better to wait until August to manage these problems if significant perennial grass weed problems exist in your lawn.

Getting back to crabgrass, there is plenty of time before a preemergence herbicide (crabgrass preventer) needs to be put down. Late April into early May is the suggested timing. Many products are available in combination with fertilizer, so spring fertilization can be done at the same time.

 

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