AMES, Iowa - Spring has sprung, and yards across the state are getting greener by the day. That means people are thinking about yard care – and how to control crabgrass, a common problem. Here are some tips from Iowa State University Extension and Outreach horticulturists on controlling crabgrass.
How do I control crabgrass in the lawn?
Crabgrass is an annual, warm-season grass. Crabgrass seeds germinate over several weeks in spring. However, plants don’t become highly visible in lawns until early summer. Crabgrass grows rapidly during warm summer weather. Growth slows with the arrival of cooler temperatures in late summer. Plants are destroyed with the first hard frost in fall. However, before it dies, a single crabgrass plant can produce thousands of seeds.
The best way to prevent crabgrass infestations is to maintain a thick, healthy lawn through proper mowing, irrigation and fertilization. Crabgrass will have a difficult time germinating and surviving in a dense stand of turfgrass. Gardeners who have had crabgrass problems in recent years will need to apply a preemergence herbicide in spring.
When should I apply a preemergence herbicide to my lawn to control crabgrass?
The keys to successful control of crabgrass in lawns are correct timing of the preemergence herbicide application and proper application of the material. A preemergence herbicide must be applied before the crabgrass seeds germinate. If the material is applied too early, crabgrass seeds that germinate late in the season will not be controlled. If applied too late, some crabgrass seeds will have already germinated. Preemergence herbicides usually should be applied in early to mid-April in southern Iowa, mid-April to May 1 in central Iowa and late April to early May in northern portions of the state.
Weather often varies considerably from year to year in Iowa. Accordingly, gardeners should make minor adjustments in the timing of the preemergence herbicide application. If the weather in March and April is consistently warmer than normal, apply the preemergence herbicide early in the normal time period. Apply the herbicide late in the recommended time period if Iowa is experiencing a cool early spring. If you’re still uncertain as to when to apply the preemergence herbicide, Mother Nature provides some helpful (colorful) clues. Preemergence herbicides should be applied when the forsythia blossoms start dropping or when redbud trees begin to bloom. Crabgrass seed germination typically begins after these events.
To ensure the herbicide is applied properly, carefully read and follow directions on the package. Also, make sure the spreader has been correctly calibrated and is working properly.
I would like to sow grass seed in some bare spots in the lawn. Can I successfully sow grass seed after the application of a preemergence herbicide?
Preemergence herbicides, such as benefin, bensulide and pendimethalin, prevent the germination of crabgrass seeds in spring. Most preemergence herbicides also prevent the germination of turfgrass seeds. If sowing grass seed in spring, the only preemergence herbicide that can be used is siduron (Tupersan). Siduron effectively controls crabgrass without affecting the germination of turfgrass seeds.
Is there a non-chemical way to control crabgrass in lawns?
Corn gluten meal is an option for gardeners who prefer a non-chemical alternative. A corn milling byproduct, corn gluten meal inhibits the root growth of crabgrass seedlings. Unable to develop roots, the crabgrass seedlings die. Corn gluten meal is approximately 10 percent nitrogen by weight, thus making it a natural “weed and feed” product. Products containing corn gluten meal are available at garden centers and other retailers.