DATE: 02/22/06

CONTACT: Clemson Extension Home & Garden Information Center, 1-888-656-9988

WRITERS: Joey Williamson and Chuck Burgess

CLEMSON - Crabgrass can be an ugly addition to an otherwise beautiful South Carolina lawn. Although it may be an unrealistic expectation to completely eliminate crabgrass from the lawn, proper lawn care and the use of a preemergence herbicide can help lawns look their best.

Crabgrass is a warm-season annual grass that grows close to the ground. As it spreads, it makes roots wherever the stems touch the soil. However, this weed relies primarily on seed for its spread through the lawn. One plant can produce as many as 53,000 seeds!

Warm season plants produce seed that germinate in the warmth of the spring. Crabgrass seeds begin to germinate when soil temperatures go above 55 degrees F for several consecutive days. The key to control is to apply a preemergence herbicide 2 weeks prior to the expected date of emergence. In South Carolina, the best time is generally between March 1st and 15 th, which coincides with the bloom time for dogwoods, redbuds and azaleas. For continued warm season weed control, a second application should be made approximately 9 weeks after the first.

Be sure to water in preemergence herbicide applications. Typically a half inch of irrigation water is necessary to dissolve the granules and uniformly coat the soil which prevents new weeds. Refer to the label for specific instructions for each product. Be aware that even after activation, low levels of soil moisture can adversely affect crabgrass control. If weed seeds germinate in dry conditions, they may not absorb enough herbicide to kill the plants.

Applying preemergence herbicides evenly is an important factor in successful crabgrass control. If a prepackaged granular product is used and the label states the amount of area it will cover, measure the turf area to accurately obtain the square footage. Furthermore, aerating or dethatching the lawn after the preemergence herbicide application may significantly disturb the herbicide barrier.

Providing the proper conditions for the turfgrass can go a long way to help reduce crabgrass in the lawn. Crabgrass thrives in infertile and sandy soils. So improving soil fertility will help the turfgrass better compete with the crabgrass.

To improve soil fertility and maintain a healthy lawn, submit soil samples to your Clemson Extension Service office for analysis. The amount of limestone that the soil needs for proper turfgrass growth will be determined by the soil test. Apply the limestone, and then apply slow release fertilizer at the appropriate times of the year for the type of turfgrass.

There are a number of cultural practices that improve the turfgrass lawn. Mow the grass at the correct height and never remove more than 1/3 of the leaf blade at one time. Water the lawn deeply and infrequently. If possible, water the lawn weekly during drought conditions. It should be noted that light, frequent irrigation may encourage weed seed germination, even if a preemergence herbicide has been applied. Fescue turfgrass should be overseeded in the fall to maintain a thick stand.

Any seeding of the lawn should be delayed by 6 to 16 weeks following the preemergence herbicide application and depending upon the product used. This is to prevent damage or death of the turfgrass seedlings. For newly seeded lawns, always wait until the new lawn is established before applying a preemergence herbicide. Do not apply preemergence herbicides to the soil before laying sod, or to new sod, as the herbicide may affect root growth. Check the product label for specific information on timing.

Many effective products are on the market for crabgrass prevention. Always read the label to determine if an herbicide will control the weed and also if it will be safe on your type of turfgrass. Remember that good cultural practices will go a long way in producing a healthy lawn.

The Clemson Extension Home & Garden Information Center (HGIC) has more information on lawns - fertilizing, establishment, renovation, mowing, watering and on specific grass types.

For answers to your gardening, pest and food safety questions, visit the Clemson Extension Home & Garden Information Center website at http://hgic.clemson.edu or call us toll-free at 1-888-656-9988.

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