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

Crabgrass, Crabgrass Everywhere!

August 5, 1999

You've probably noticed lots of light colored, coarse grass appearing and growing rapidly in lawns and other turf areas. This is crabgrass, and the summer of 1999 has been a great year for it to grow.

Crabgrass is a warm-season annual grass. It likes full-sun, heat, and moisture. The weather over much of July has provided heat and enough rain for crabgrass to flourish. Another factor has been dry weather over much of June, and for some areas, July. This dry weather slowed down the growth of lawn grasses. The heat of July has also slowed most cool-season lawn grasses down.

With the lawn grasses slowing down, the crabgrass gets a chance to invade. With heat and moisture, it develops very quickly and aggressively. The good news about this weed is the fact it is an annual and will die off in early fall. Thus even though the lawn may be infested now, the only way the problem returns next season is by crabgrass seeds germinating and developing into new plants.

On many lawns, preemergence crabgrass herbicides were used this spring, yet the crabgrass still appeared. Keep in mind these herbicides that kill crabgrass seed as it germinates are not likely to give 100 percent control. A small percent of crabgrass seed may "escape" and germinate. In a season such as this, that percent may look very large as the plants flourish, get larger, and more visible.

Another big factor, whether a preemergence herbicide was used or not, is the impact of good cultural practices on crabgrass. Mowing higher is probably the most important. Mow in the 2-1/2 to three-inch range and fewer crabgrass problems will develop. Also water properly. Watering too much, keeping soil saturated, or in frequent, small amounts favors crabgrass.

Right now, not much can be done. There are some postemergence crabgrass herbicides, but they work best on very small plants. Work on getting the lawn thicker this fall and next spring. Consider a preemergence herbicide next spring, along with following a sound lawn care program. And last but not least, realize that certain years bring weather patterns that can offer big advantages to weed problems like crabgrass.


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