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

Problems with Warm Season Grasses

November 13, 1997

Are there patches of straw-colored grasses in your lawn this fall? Is the entire lawn now a straw color? If so, there is a good chance you are dealing with a warm season grass.

Warm season grasses turn dormant as cool weather returns in fall, and do not return to a green color until very late spring or early summer. For most of fall and spring, they are a strong contrast from the cool-season grasses typical of area lawns, which are green.

Zoysiagrass is the most common warm-season grass in our area. Advertisements promote this grass as a thick carpet of green, despite the heat. During a hot summer, such as back in 1995, the zoysiagrass lawn was most likely the greenest on the block. However, in cooler summers, such as this past year, it probably did not stand out from other lawns.

Then with the return of cool weather in September, zoysiagrass starts turning yellow, then a straw color. It is not dead, but it will not green up until significant warmth returns sometime next year. Some homeowners have been complaining the patches seem larger, or never existed before. Most likely the zoysiagrass did well back in one of the hot summers and invaded more of the stressed lawn, thus the patches are now larger.

One control option for zoysiagrass is to dig it out, making sure to get all the stolons and rhizomes (creeping stems). Another option is to apply the herbicide glyphosate (Roundup, Kleeraway), but the grass needs to be green and growing to be killed. Probably the best time to do this would be next August, so the area can be reseeded afterwards.

Another question often asked concerns the possibility of seeding Kentucky bluegrass or perennial ryegrass into the patches, with the idea the cool-season grass will overtake the zoysiagrass. This is not likely to occur, as even dormant zoysiagrass is very thick and resists invasion.

An additional warm season grass that has been appearing as strawlike patches in recent days is nimblewill. Nimblewill will appear as patches of fine grass, usually in shade locations. These patches become very conspicuous now and in spring. Control options are the same as for zoysiagrass.


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