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Controlling Crabgrass

North Dakota lawn grasses, Kentucky bluegrass and red fescue, are perennial cool season grasses. Crabgrass is a warm season annual grass which grows best in the heat of mid-summer when desirable lawn grasses are often semi-dormant and offer little or no competition. Crabgrass overwinters as seed, comes up about mid-May (about the time forsythia begin to bloom) and later, and is killed by fall frosts. Crabgrass is not shade tolerant and grows best in full sun.

Control crabgrass as follows:

Step 1

Fertilize the lawn in late summer and spring to develop a dense, healthy stand of grass. Fertilized bluegrass does not go into mid-summer dormancy as soon as unfertilized bluegrass.

Step 2

Set the mower to cut at 2 1/2 to 3 inches. The taller height of cut produces more shade at the soil surface and inhibits crabgrass germination.

Step 3

Apply a pre-emergence crabgrass herbicide such as Dacthal in early May. You can usually buy these herbicides in granular forms. The herbicides kill germinating crabgrass seedlings. One application protects for the growing season.

Most pre-emergence herbicides work best before germination occurs. Generally, after crabgrass has germinated, it will not work. You must apply it before the seeds germinate. Those newer herbicides that have both pre - and post - emergence activity will say so on the label.

If you have more questions, please contact your county office of the NDSU Extension Service and request circular H-1009, "Weed Control in North Dakota Turfgrasses."

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