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YARD AND GARDEN

Crabgrass control

Crabgrass is often considered the scourge of home lawns. With the possible exception of dandelions, no other weed creates as many headaches, or is responsible for a large portion of the lawn care product market.

David Robson

One of the worst things about the plant is that it's one of the most difficult to control once it has sprouted. Next to impossible would be more exact.

Now, I'm a firm believer that hardly anyone can tell the difference between bluegrass and crab-grass at 30 miles per hour, let alone 55 miles per hour on rural roads. Crabgrass may give the illusion of a green yard during July and August. Unfortunately, it dies with the first frost, leaving large brown holes in your yard.

Many homeowners view crabgrass as an annual weed because of its size and appearance. Leaf blades tend to be four to ten times wider than bluegrass, giving the plant a coarse appearance.

Homeowners could probably live with the coarse appearance if the plant grew like bluegrass, spreading over the ground and thriving nine months out of the year. It doesn't.

If you don't mow crabgrass, it tends to grow upright. However, the first mowing drives the plant into a prostrate mode, shading and smothering the nearby turf plants.

The most common crabgrass is the hairy crabgrass. Leaves are fuzzy and stems are rolled. The seed head has three to nine branched "fingers," giving the plant a bird's foot appearance, or one with nine toes. Each finger can produce a hundred seeds. The seed stalk grows upright, until it's mowed once, and then it tends to grow horizontal, below the mower blade. This definitely is a plant that adapts quickly to the environment.

Crabgrass starts germinating when soil temperatures are 50 to 55 degrees Fahrenheit for ten or more days. Germination can take place over six weeks, depending on soil moisture and air. A wet spring may prevent the seeds from germinating into May or June. Most seeds will germinate in April during a warm, dry year.

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

Crabgrass seeds need light and an open space to grow. Make sure you don't mow bluegrass, ryegrass and fescue lawns below two inches tall.

Pre-emergence herbicides provide excellent weed control for crabgrass. The compound doesn't prevent the weed seed from germinating, but kills the newly sprouted seedling. Timing is everything. Make sure you apply the products before the seeds germinate.

Early April is an ideal time to apply pre-emergence control. The ideal product would contain just the crabgrass preventer and no fertilizer. Early spring (April) fertilizing can stimulate grass shoot growth at the expense of root growth. Research has shown that spring fertilizing should be held off until early May, around Mother's Day. Of course, you can then use those crabgrass-fertilizer combinations.

There are pure crabgrass preventers on the market. Several companies make them. Ask your local store to obtain the products, if possible.

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 (around Mother's Day) helps control many warm season grasses such as goosegrass, foxtail and barnyard grass.

If is difficult or next to impossible to sow grass seed in the spring and control crabgrass. Weedkillers aren't able to distinguish between different types of grasses. Germinating bluegrass or fescue seeds will be killed along with the crabgrass seedlings. You may be better off waiting until fall to sow grass seed.

Make sure to read and follow all label directions when applying pesticides.

David Robson is an Extension Educator, Horticulture, at the Springfield Extension Center, University of Illinois Extension. You can write to Robson in care of Illinois Country Living, P.O. Box 3787, Springfield, IL 62708.
Telephone: (217) 782-6515.
E-Mail: robsond@mail.aces.uiuc.edu

18 ILLINOIS COUNTRY LIVING APRIL 1999