Q: Last year, my lawn had several areas of crabgrass. How should I deal with this?
A: Crabgrass (Digitaria sanguinalis) is an annual weed that germinates in midspring and gradually colonizes bare spots in the lawn during hot summer weather before producing a crop of seeds and dying off in the late summer. The first line of defense against crabgrass is to minimize the opportunities for it to proliferate by maintaining a healthy lawn through appropriate mowing, fertilization, and watering.
If you have been troubled by crabgrass in prior years, consider applying a pre-emergent herbicide to your lawn just before the crabgrass seed germinates. Germination takes place when the soil temperature consistently reaches 60 degrees Fahrenheit, which is typically in late April or early May in northern Illinois.
Several synthetic pre-emergence herbicides are commonly used for crabgrass control. These are available to homeowners either as standalone granular products, or combined with a spring fertilizer. If you intend to overseed your lawn in the spring and wish to apply a synthetic pre-emergent herbicide, be careful to use a product that is clearly labeled for use on newly seeded lawns. Do not apply pre-emergent herbicides before the temperature of the top 2 inches of soil consistently reaches 50 to 55 degrees, which typically happens around mid-April in northern Illinois. Please contact Plant Information at @email for specific herbicide recommendations.
An organic alternative is the use of corn gluten meal. It is offered by several manufacturers and sold at most garden centers. In northern Illinois, corn gluten meal should be applied in late March through early to mid- April. Corn gluten meal products differ from manufacturer to manufacturer, so be certain to follow the manufacturer’s instructions. Corn gluten meal does not work as quickly as the synthetic herbicides and applications may need to be repeated over several seasons to achieve effective control. An added benefit of corn gluten meal is that it contains about 10 percent nitrogen by volume and is an effective slow-release lawn fertilizer.
As always, to protect yourself, others, and the environment, be certain to read and follow all of the safety and application instructions included with the product labels.