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Act now to control crabgrass in the home lawn

As the weather turns warmer, many homeowners begin to take an interest in the care of their home lawns.

The warm season turf grasses, like bermuda, centipede and zoysia, are beginning to come out of dormancy and greening up. The cool season fescue is actively growing. Here at Gwinnett County Extension, a high percentage of the calls we receive are on lawn care. One of the most frequent questions is about controlling crabgrass, a dreaded weed in the home lawn.

From late spring to the first frost, crabgrass can invade large portions of the lawn, creating an unsightly appearance. Three species of crabgrass invade our lawns - large crabgrass, southern crabgrass and smooth crabgrass.

They all have similar growth and appearances, with some minor differences in their leaves. Crabgrass is troublesome because it is an annual weed, and a single crabgrass plant can produce 150,000 seeds in one season. Also, by being such a prolific summer annual weed, it out-competes the grass we do want to grow. It then dies out in the cold weather, leaving large dead voids in the turf. Despite being an undesirable weed, it is sometimes used as a forage crop for horses and other farm animals.

As the daily temperatures become warmer, the crabgrass seeds will begin germinating. The best way to prevent it is with pre-emergent herbicides (weed killers). Several effective brands of crabgrass pre-emergent weed killers are on the market, and can be purchased by the homeowner at any garden center.

Most are granular, and can be put out with a drop spreader. If applied according to label directions, they provide good control of crabgrass. The best time of the year to make the application is in early March, when the temperatures are above 60 degrees for several days in a row. When the forsythia shrubs are in bloom is generally a good rule of thumb for making the application. After the application, water the lawn in thoroughly.

These herbicides are recommended only for lawns that are well established. Do not apply to lawns that have been recently seeded, or have newly laid sod.

After the crabgrass has emerged, control is very difficult. Some post-emergent herbicides (ones that kill weeds after they have emerged), are effective in controlling the weeds only when they are small, when they are difficult to detect. So, application of the pre-emergent is generally the best way to go in dealing with this weed.

Healthy lawns with dense stands of grass are more resistant to crabgrass infestation. The crabgrass likes to grow in bare areas and on turf that is stressed. Proper fertilization, mowing and watering will promote more vigorous growth and development of the turfgrass, thus reducing the ability of the crabgrass, and other weeds, from being a problem.

Water the lawn more deeply and less often. Good, thorough soakings a couple of times a week will promote healthy, deep root growth. Mow the turf as high as possible, allowing the grass to shade out any emerging crabgrass, and other weed seedlings.

Although crabgrass is an aggressive weed and can be difficult to control, proper timing and use of the pre-emergent herbicides and correct cultural care to maintain a healthy lawn will reduce their ability to spread.

Timothy Daly is an agricultural and natural resource agent with the Gwinnett County Extension Service. He can be reached at 678-377-4010 or timothy.daly@gwinnettcounty.com.