If you have recently noticed rusty-brown patches of dead grass showing up in your lawn, you may have an infestation of crabgrass – though the dead grass is from last year.

Last summer's drought and high temperatures were stressful for many area lawns. Some lawns thinned and died, while others became infested with hardy weeds.

"Crabgrass is an annual weedy grass that, from a distance, blends into your lawn during the summer," explains David Robson, University of Illinois Extension horticulture educator. "Upon close inspection, it can be identified by its wide leaf blade and light green color. During the summer, this low-growing weed will also have a seed spike that looks like a turkey foot."

The seeds turn a lovely maroon color with cool temperatures. Freezing temperatures kill this pesky weed, leaving you with splotches of brown throughout the green lawn.

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

Robson says the primary way to control crabgrass is to provide 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 from germinating seeds that have absorbed the weed killer.

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 six to eight weeks after the first, 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.

"Rains in mid-summer often provide excellent conditions for crabgrass germination," says Robson. "If you don't make a second application of a crabgrass pre-emergence weed killer, you may be leaving your lawn wide open for crabgrass to invade."