This herbicide effectively controls crabgrass without affecting the germination of the turfgrass seeds. Gardeners can also control crabgrass by applying corn gluten meal. A corn milling byproduct, corn gluten meal inhibits the root growth of crabgrass seedlings. Unable to develop roots, the crabgrass seedlings die. In addition to crabgrass, corn gluten meal offers pre-emergent control of dandelion, plantain, lambsquarter and other weeds.
Products containing corn gluten meal are available at garden centers and mailorder companies.
The keys to successful control of crabgrass in lawns are correct timing of the preemergence herbicide application and proper application of the material. Preemergence herbicides must be applied before the crabgrass germinates. If the material is applied too early, the crabgrass that germinates late in the season will not be controlled. If applied too late, some crabgrass will have already germinated. Weather often varies considerable from year to year in Iowa.