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 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.
Fertilize the lawn in late summer or fall and again in spring to develop a dense, healthy stand of grass. Fertilized bluegrass does not go into midsummer dormancy as soon as unfertilized bluegrass.
Pre-emergent applications made when soil temperature are still below 60 are the best prevention. 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. Pre-emergent applications lose their effectiveness if the lawn is raked or disturbed during the first half of the growing season.
There is a new product that allows for pre-emergent crabgrass control over areas that have been seeded. We use this special formulation to prevent crabgrass, barnyard-grass and foxtail and to seed your lawn at the same time. This product and others containing Siduron™ are most commonly used.
Post-emergence crabgrass herbicides are 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.
