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nimbleweed

Three grassy weeds in the lawn


Master Gardeners and Extension offices are getting many calls on lawns right now, especially when it comes to weeds. Dandelions and other broadleaved weeds are easily identified in the lawn. Some that are harder are the grassy weeds; those that look similar to our desirable grasses, just a bit different. Here are some common questions and answers from our Master Gardener Help Desks:

Q: I have patches of stringy straw- or tan-colored grass in my lawn that is not greening up like the rest. What is it?

A: This grassy weed is a warm season perennial called nimblewill. Nimblewill will not green up until both the soil and air temperatures get warmer and then it blends into the rest of the lawn. Leaf blades are slightly wider than our bluegrasses, which make up most of our lawns in northern Illinois. Nimblewill can grow in full sun to partial shade. It will go dormant earlier than our cool season lawn grasses too, so you will see that straw-colored patch come back this fall.

Q: What is the grass that always outgrows my bluegrass lawn with wider grass blades, and two or three days after I mow it is easily an inch or taller than surrounding grass?

A: This one is tall fescue, one of our cool season perennial grassy weeds that will turn green at the same time as our lawn grasses. Tall fescue grows with a bunch type root system that allows our lawn grasses to grow into the crown so there is no clear base to see. It will have a slightly different green to the wide and deeply veined leaf blades. Tall fescue has good drought tolerance and can tolerate some shade as well. In this form, we consider tall fescue a grassy weed. Since it has such good drought tolerance, grass breeders actually have been introducing new varieties called "turf type tall fescues," which are now available as seed and sod. In that case, it is not considered a weed, but instead a desirable grass for lawns in droughty locations. It matches our bluegrasses in color, leaf blade width and growing height. If lawn watering restrictions remain or get more restrictive, turf type tall fescue will likely gain importance.

Q: I have a grassy weed that spreads by underground stems and is not controlled with crabgrass preventer, what is it?

A: This is a grassy perennial weed called quackgrass, which spreads easily by those underground rhizomes. It can spread from seed, but since we mow the lawn, seed heads rarely get a chance to form, flower and set seed. Often times it escapes from a perennial bed where it may never be completely controlled. It is impossible to control by just pulling, as the rhizome remains several inches below the soil surface and sprouts back up from there. This one has the widest blade of the three discussed here and it is the one with a color that least matches our other lawn grasses. Since this is a perennial grassy weed, a crabgrass preventer that acts against seed is not effective on quackgrass unless from seed.

Richard Hentschel is a Horticulture Extension Educator with University of Illinois Extension, serving DuPage, Kane and Kendall counties. Stay tuned to more garden and yard updates with This Week in the Garden videos at facebook.com/extensiondkk/videos and the Green Side Up podcast at go.illinois.edu/greensideup. The Kendall County Master Gardener Help Desk is open for 2018. Current hours are Monday through Friday from 9 a.m. to 12:30 p.m. at 630-553-5823.



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