Many homeowners call any grassy weed that they don’t like, or don’t recognize, as being crabgrass. Professional lawn care providers are often flooded with calls in early spring (northern climates) that crabgrass is growing and can they do anything about it. Of course, in early spring, crabgrass has not yet started to develop, but “crabgrass” is one weed name that most people can remember. Everyone knows what a dandelion looks like, but there’s plenty of people that don’t know what other weeds look like.

Crabgrass is a warm season annual grass which grows best in the heat of midsummer when desirable lawn grasses are often semi-dormant and offer little or no competition. Crabgrass overwinters as seed, comes up about mid-May or later, and is killed by the first hard frost in fall. Crabgrass grows prostrate and close to the ground, the stems extend out like the legs of a crab and it is usually lighter in color than the desirable lawn grasses. If you conclude that crabgrass was present last year, then it is likely that it will be a problem later on this year.

Crabgrass grows best in full sun. It does not grow in shady places. Crabgrass can be controlled in a number of ways, but the best defense against crabgrass is a thick vigorously growing lawn that is mowed no closer than 2 1/2″ for cool season grasses.

Once the seed has germinated, pre-emergent controls will not be effective. Post-emergent controls are going to be the most effective if they are applied while the young plants are tender and just getting established. Time your applications to assure that most of the seeds have germinated or make more than one application.

Pre-emergent applications should be made when soil temperature are still below 50 for the best prevention of crabgrass. Pre-emergent applications are not recommended for areas where new grass seed is going to be planted during the first half of the growing season. Preemergent applications lose their effectiveness if the lawn is raked or disturbed during the first half of the growing season.

Once the crabgrass seed has germinated, pre-emergent applications are not effective. When this occurs a postemergence crabgrass herbicide is now available. These are products that are applied after the crabgrass seed has sprouted. The herbicide (ACCLAIM) gives excellent crabgrass control with one application. This product should be applied when crabgrass is in the 3 to 4 leaf stage of development. Once crabgrass has become established during the growing season, it is best to leave it alone and it will die back in the fall. Next season, apply a pre-emergent herbicide to control it. Overseed areas that were heavily infested with crabgrass in early fall to help fill in those areas.

Ever notice when the weather heats up and drought conditions appear, that crabgrass seems to thrive? With the extreme heat and drought stress of summer and the loss of grass to things like billbug and brown patch, thin areas in many lawns are overtaken by crabgrass.

This is likely large crabgrass, which tends to germinate later than smooth crabgrass. With ample moisture in early summer, lots of sunny days and high temperatures, crabgrass seeds that were present in these thinned areas were opportunistic and germinated. There is nothing to do about crabgrass late in the season. Because crabgrass is an annual plant, it will die out with a killing frost. Take note of the infested areas, however, and be prepared to apply a pre-emergent herbicide in those areas early next spring; both organic and synthetic herbicides are available.