Crabgrass - Digitaria spp

This is not a noxious weed, but it is a common weed that can be a problem.

Crabgrass is one of the most prevalent grassy weeds found in lawns. Crabgrass thrives in full sunlight and high temperatures and can easily out compete common cool-season grasses under these conditions. Crabgrass is in a group of plants known as summer annuals. These plants have a life of less than one year. Summer annuals germinate in the spring, grow through the summer and die with the first hard frost. These plants produce a tremendous amount of seed in the mid- to late summer when the day length starts to shorten. These seeds ensure next year’s crop of weeds but can also remain dormant in the soil for several years before germinating. It is likely that if you have crabgrass in your lawn, it will be there next year, too. 

Cultural Control

Weed management in turfgrass  can be accomplished in various ways. Traditional methods include cultural management and mechanical and chemical controls. The primary and most effective weed control tactic in a lawn is proper mowing. In fact, it has been estimated that regular mowing eliminates some 80 percent of weedy species. Other cultural practices, such as judicious fertilization, can further reduce weed competition by increasing turfgrass vigor. Open and weak turfgrass areas promote crabgrass infestations because of higher soil temperatures, which enhance germination and decrease competition. The best defense against weed invasion is a dense, healthy turfgrass stand. This is particularly effective for annual weeds such as crabgrass that establish from seed every year. A thick turf canopy can effectively shade the soil and reduce the number of seedlings that are able to establish. Crabgrass germinates in the spring, quickly filling in bare spots.

Preemergence Timing

Knowing when crabgrass is likely to be present is helpful in proper identification and control. Homeowners who complain of crabgrass infestations in April and May are usually identifying tall fescue, nimblewill or quackgrass. Crabgrass germination typically begins in early May when soil temperatures reach 62 degrees Fahrenheit at a depth of 1 to 2 inches.

To be effective, preemergence herbicides must be in place before germination occurs. Preemergence treatments are preferred because they are generally more effective for crabgrass control and less injurious to the turfgrass than postemergence treatments. In general, preemergence herbicides should be applied when soil temperatures reach 50 to 55 degrees Fahrenheit. Preemergence herbicides work by inhibiting the growth of young seedlings. These products do not eliminate established plants and must be applied before germination begins. 

Postemergence Applications

Once crabgrass has established, preemergence herbicides will not be effective. Only a few herbicides are available for use on young plants. Metharsenate (MSMA) is the most common herbicide found in postemergence crabgrass products available to homeowners. Two or three applications spaced seven to 10 days apart are often needed to achieve acceptable control. Unfortunately, some turfgrass discoloration often accompanies applications of metharsenate herbicides. Dithiopyr (Dimension, Spectracide Crabgrass) also has postemergence activity on one- to three-leaf crabgrass.

In general, preemergence applications are preferred in lawns with a history of crabgrass pressure because of the difficulties associated with postemergence control. Preemergence herbicides and proper turfgrass management are the best combination for long-term crabgrass suppression. Be sure to read, understand and follow all directions on the herbicide label.

* Call 509-943-6005 or email for control options