Death and taxes are inevitable, as the old saying goes. So, it seems, is crabgrass. Crabgrass is often considered the scourge of home lawns.

"With the possible exception of dandelions, no other weed creates as many headaches or is more responsible for a large portion of the lawn care product market," says David Robson, University of Illinois Extension horticulture educator. "Unfortunately, it's one of the most difficult to control once it has sprouted. Unlike most of the desirable turfgrasses, crabgrass will flower below the mower blade."

Crabgrass is a weed because of its size and appearance. Leaf blades tend to be three to four times wider than bluegrass, giving the plant a course appearance. Homeowners could probably live with the course appearance if the plant grew like bluegrass. However, it doesn't. Crabgrass tends to be an open or prostrate plant that shades and smothers the nearby turf plants.

The most common crabgrass is the hairy crabgrass. Leaves are fuzzy, and the stems are rolled. The seed head has three to nine branched "fingers," giving the plant a bird's foot appearance. Each finger can produce a hundred seeds.

Not quite as common is the smooth grass. The plant is smaller, not hairy, and has a purplish stem.

Crabgrass is sometimes called watergrass, though other weedy plants carry the same name. Crabgrass starts germinating when soil temperatures are 50 to 55 degrees for ten or more days. Germination can take place over six weeks.

"Proper lawn maintenance practices limit crabgrass invasions," explains Robson. "A dense stand of turfgrass prevents the weed from germinating and establishing. Fall fertilizing, overseeding, aeration and thatch control can limit spring problems."

Pre-emergence herbicides provide excellent weed control for crabgrass. The compound doesn't prevent the weed seed from germinating, but it kills the newly sprouted seedling. Early April is an ideal time to apply pre-emergence control. Contact your local U of I Extension office for the current recommended products. The majority of pre-emergence weed control compounds will provide protection for four to six weeks. A follow-up application four to six weeks after the first application helps control many warm-season grasses such as goosegrass, foxtail and barnyard grass.

Robson says it is difficult to sow grass seed in the spring and control crabgrass. Weedkillers aren't able to distinguish between the different types of grasses. Germinating bluegrass or fescue seeds will be killed along with the crabgrass seedlings.

The compound siduron (Tupersan) can be used to control crabgrass while allowing for some grass seeding. However, the chemical must be used at half the rate listed on the package to prevent damage to grass seed. As always, read and follow all label directions when applying pesticides.

This information is for educational purposes only. References to commercial products and trade names do not constitute endorsement by the University of Illinois and do not imply discrimination against other similar products that are not listed.

Source: David J. Robson, Extension Educator, Horticulture, drobson@uiuc.edu