URBANA, Ill. — When confronted with lawn weeds, typically we think of dandelion, creeping Charlie, and violet. These plants and many others are classified as broadleaved weeds, or dicots, and are easily distinguished from grasses which are monocots. Scientists have engineered herbicides that target broadleaved plants, while the chemical does not affect desirable turfgrass.

But what happens when you have a grassy weed appear in your lawn? Selective lawn herbicides containing 2, 4-D or dicamba, are useful in controlling broadleaves, but will not work on grasses, says Chris Enroth, University of Illinois Extension horticulture educator.

Annual grasses, such as crabgrass, are best controlled with a preemergent herbicide applied before the offending weeds germinate. Once the seed has germinated a homeowner should practice good lawn care culture that can make a lawn more competitive with the weeds.

Perennial grassy weeds like quackgrass or nimblewill are becoming more common in home lawns. “They are difficult to control because they are perennial, meaning they come back year after year,” Enroth says.

And since cool-season grassy weeds, like tall fescue, match the lifecycle of our desirable cool-season turfgrass species, this makes it difficult to find a targeted timeframe or chemical that will kill the offending plant, but leave the desirable turfgrass. Often, homeowners must resort to spraying a non-selective herbicide, such as glyphosate, rake out the dead patch, and reseed with their desired species of turf.

Enroth says lawn herbicides containing mesotrione have shown to be effective at controlling some troublesome grassy weeds like nimblewill. Other products are a bit pricey and best left to professional lawn care companies, and most can only legally be used by licensed applicators.

“I do not spray herbicides on my lawn," Enroth says. “I practice good lawn culture which gets me about 80% of the way to a perfect lawn. The other 20% is easy to live with.”

With this approach, Enroth looks for established vegetation. He defines a successful lawn as a groundcover that won’t erode and send sediment into the streams and rivers, plus, the plants must tolerate family activities. The benefit of weeds is that they are still green. The added benefit of weedy grasses is that at least they blend in, more or less, with the turf.

Proper lawn care practices

1. Mow high – Set the blade to almost the highest setting (3½ inches). Cool season grasses, like turf-type tall fescue, prefer this height.
2. Sharpen blades – Getting a mower’s blades sharpened can make a world of difference and will cut your lawn instead of beating up the lawn with a dull blade.
3. Avoid high amounts of nitrogen in the early spring. The grass grows fast enough at that time of year. If you will only fertilize once, opt for the late summer to early fall for cool-season lawns.
4. Overseed from late summer to early fall.
5. Keep it clean. Pick up after pets.
6. Stay on top of mowing. Avoid removing more the 1/3 of the leaf blade to not stress the lawn.

For more information on lawn care, connect with your local Illinois Extension county office at go.illinois.edu/ExtensionOffice.

WRITER: Chris Enroth, Horticulture Educator, University of Illinois Extension

PHOTO ACCESS: The photo in this article is available to download for media use. 

Photo by Chris Enroth. Perennial grassy weeds like quackgrass or nimblewill are becoming more common in home lawns.