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 Grassy Weeds in Lawns

March 29, 2001

Last week, crabgrass, which will not be appearing in lawns for several weeks, was the topic of discussion here. What about patches of weedy grass that are visible in lawns early in spring? Chances are these are perennial grassy weeds, which are difficult to manage in lawns.

Many perennial grass weeds, such as tall fescue, are desirable grasses when growing by themselves but become weeds when mixed in Kentucky bluegrass lawns because of different texture, color, or growth habit. Tall fescue is coarser and grows in mounded clumps. Creeping bentgrass appears as patches of finer grass, usually lighter in color. Zoysiagrass appears as thick patches of dormant grass for much of spring and fall in bluegrass lawns.

One way to distinguish perennial grasses from annuals is the time of the year established plants are present. Perennials are very visible established green grasses in spring whereas annuals (i.e. crabgrass) take considerable time to appear. Crabgrass plants are not yet visible this season. Most annuals die off quickly in fall, but perennials do not.

Tearing out these weed patches by hand is one control option. It's important to get all of the plant, as many have rhizomes or stolons. These modified stems enable these species to spread quite readily, so if broken or cut, they regrow.

Unlike annual grasses (crabgrass), herbicides applied to the perennial weed grasses will also damage the lawn species. For this reason, spraying over the lawn is not suggested unless the problem is so bad all grasses need to be killed and the lawn renovated (reseeded). Using a nonselective herbicide, such as glyphosate (Roundup, Kleeraway), patches of the undesirable species can be spot treated. After weeds and portions of lawn hit with spray die, reseed with desirable grass species. Treating in mid-August is generally thought of as the best timing, as late August into early September is the most favorable time for reseeding. Keep in mind the weed species needs to be actively growing to be controlled by glyphosate.


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