University of Illinois Extension

You've Got Crabgrass, Now What?

If you have a lawn, you likely have had some crabgrass somewhere in the yard despite your best efforts, says Richard Hentschel, University of Illinois Extension green industry specialist.

"The weather for both rain and temperatures has really challenged the homeowner this year," said Hentschel.

"Crabgrass, also commonly called 'Water grass' is an annual grass that needs warm soil temperatures and adequate soil moisture to sprout and invade our lawns. Crabgrass can germinate all season long if conditions are right."

There are two common kinds of crabgrass, smooth and large, differing in appearance, both producing seed on thin finger-like seed heads. Crabgrass germinates, grows, flowers and sets seed in a single season. Crabgrass relies on producing a large amount of seed for future generations, since the plant itself will die at the end of the growing season. This is different than our perennial lawn grasses like Tall Fescue or Quack Grass that come back every year once they establish themselves in your lawn from vegetative plant parts.

"Crabgrass management can take several different directions," he said. "The most common is likely to be the application of crabgrass preventer. These materials either inhibit the seed from germinating or kill it before the young crabgrass plant emerges from the soil. These materials are preventative in nature and must be in place before any crabgrass seed can germinate.

"Also, these materials have a defined life span and if applied too early in the spring, will break down and allow crabgrass seed to germinate later in the summer."

One option to avoid this is to apply your preventer and the spring fertilization separately, Hentschel added. If crabgrass is a serious problem, homeowners should consider a mid-summer crabgrass preventer application to carry the protection through fall. If you disturb soil surface, top-dress (may have weed seed in the new dirt), aerate in any way, you will break the barrier of protection and you can have crabgrass germination anyway.

"There are a number of products on the market that will control crabgrass after it has germinated too," he said. "Timing is critical, younger crabgrass plants are more readily controlled than older, more established plants. Crabgrass will not immediately die with these products, taking several days to begin to show signs of decline."
How you manage your lawn also influences the potential for crabgrass and weeds in general. Lawns mowed on the short side will expose more soil to sunlight, increasing the chance of germination. A lawn mowed higher will shade the soil and also conserves soil moisture for the lawn, making it more competitive.

As crabgrass grows, it radiates out in a circular pattern, covering over your desirable lawn grasses. It can also root down into the soil at spots along the stem, making it hard to pull out. You hardly ever see just a single crabgrass seedling; they are more likely in groups, quickly covering those thin spots in the lawn.

"If you see the crabgrass seedling early enough and you only have just a few, they pull out very easy as the root system is not yet developed," he noted. "Crabgrass will have a much lighter green color and a wider leaf blade than your lawn grasses, so spotting it is not difficult."

As a bonus, since crabgrass preventer works against annual grasses, other grasses like foxtail, goosegrass, fall panicum, and barnyard grass will also be controlled.

"When using a crabgrass preventer, read the label carefully for the re-seeding interval because these materials will prevent your desirable grasses from germinating as well," Hentschel said. "If you intend to re-seed your lawn, avoid putting preventer on those areas."