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John Fulton

John Fulton
Former County Extension Director

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In The Backyard

Horticulture columns and tips done on a timely basis

Controlling Crabgrass - from David Robson

Posted by John Fulton -

If you have recently noticed rusty-brown patches of dead grass showing up in your lawn after a frost, you may have an infestation of crabgrass.

Crabgrass is an annual weedy grass that, from a distance, blends into your lawn during the summer. Upon close inspection, it can be identified by its wide leaf blade and light green color. During the summer, this low growing weed can also be identified by its seed spike that looks like a turkey foot. The seeds turn a lovely maroon color with cool temperatures. Freezing temperatures kill this pest leaving you with splotches of brown throughout your green lawn.

As an annual, crabgrass seeds germinate during late spring and summer and die with the first frost. Plants do not overwinter.

The primary means of controlling crabgrass is by providing a vigorous, dense, competitive turf. Thin, weak lawns should be treated with a pre-emergent crabgrass weed killer to prevent infestation.

Pre-emergence weed killers, for controlling crabgrass, are applied to lawns in early spring to prevent the appearance of crabgrass. The "crabicide" forms a chemical barrier or blanket at the soil surface that prevents crabgrass development from germinating seeds that have absorbed the weed killer.

In central Illinois, crabgrass pre-emergence weed killers are generally applied in early to mid April. Because this protection does not persist for the entire season, University of Illinois turf specialists recommend a second application of pre-emergence crabgrass weed killer be applied 6 to 8 weeks after the first application at half the recommended rate.

The second application should be made about mid May. This second application will provide extended control of crabgrass that may get started in June.

If you are in southern Illinois, applications should begin the middle of March. For those in northern Illinois, you may be able to wait until mid-April for the first application.

Rains in midsummer often provide excellent conditions for crabgrass germination during this period. If you did not make a second application of a crabgrass pre-emergence weed killer, you may be leaving your lawn wide open for crabgrass to invade.

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