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Control of Crabgrass in Homelawns Zac Reicher and Clark Throssell Purdue University Turfgrass Specialists

AY-10

Crabgrass is the major weed infesting homelawns in Indiana. Crabgrass is an annual weed germinating in April, setting seed in August, and dying with the first frost of fall. Crabgrass has tremendous survival reproductive capabilities. Because of this, it is unrealistic to expect no crabgrass plants in your lawn. You cannot eradicate crabgrass (or any other pest for that matter); a few crabgrass plants in your lawn are acceptable.

Cultural Crabgrass Control
The most effective way to control crabgrass is to create a dense, healthy turf. A healthy turf will compete well with crabgrass and prevent it from establishing.

Mowing

• Mow at 2.5 to 3.5 inches.
• Mow frequently so as not to remove more than 1/3 of the leaf blade at one time. This may mean mowing twice weekly in spring and every other week in summer.

Irrigation

• Irrigate deeply and infrequently. Water to wet the soil to the depth of rooting, and then do not water again until you see the first sign of drought stress. The first sign of drought stress is a bluish grey hue of the grass or footprints remaining in the turf after it is walked upon.

Fertilization

• Fertilize to create as dense a lawn as possible applying 2 to 4 pounds nitrogen per 1000 ft².
• Apply 60-100% of the nitrogen in two applications in Fall: one in September and one in November after the final mowing.

Herbicidal Control
Often, cultural control alone will not control crabgrass satisfactorily, and herbicides may be needed. This is especially true in new lawns or lawns that are thin from damage or improper maintenance. When using herbicides and all pesticides, be sure to read, understand, and follow all label recommendations.

Preemergence Herbicides
Preemergence herbicides prevent emergence of crabgrass plants. These products must be applied prior to crabgrass germination which could occur as early as April 1 in southern Indiana and three or more weeks later in northern Indiana. Purdue research has shown that these herbicides can be applied as early as March 1 and still be effective all season. It is essential to apply these products early in spring prior to crabgrass germination.

Often, preemergence herbicides are combined with fertilizers. Since fertilization should be minimized in the spring, purchase products with most of the nitrogen in slow release forms such as methylene ureas or sulfur or polymer coated ureas. Avoid products with most of the nitrogen as urea or ammonical nitrogen.

Do not use these products on new seedlings or before seeding an area. To be most effective, these products need to be watered- in after application. Refer to the label for specific instructions of each product.

Postemergence Herbicides
Postemergence herbicides control crabgrass after it has emerged. These products are most effective on small crabgrass. These products are more difficult to use than preemergence herbicides and it is extremely important to follow label instructions. Keep in mind the following when using these products:

• The area must be well-watered and not under drought stress.
• Do not mow or water for 24 hours following application.
• Apply at temperatures below 85ºF. These products are most effective on clear days with low humidity.
• A second application may be needed within seven days for most effective control.
• Refer to the label for use before and after seeding.

Do not attempt to control crabgrass after about July 15, because crabgrass is too large to control effectively. It is better to simply tolerate the crabgrass until it dies with the first frost.

By maintaining a dense lawn, you can limit the amount of crabgrass. Proper fertility, mowing, and irrigation is essential for crabgrass control; consider herbicidal control only if necessary.

Purdue University

Indiana 47907

3/98

Cooperative Extension work in Agriculture and Home Economics, state of Indiana, Purdue University, and U.S. Department of Agriculture cooperating;
H. A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the acts of May 8 and June 30, 1914.
The Purdue University Cooperative Extension Service is an equal opportunity/equal access institution

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