University of Illinois Extension
Bruce Spangeberg

These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area.

Stateline Yard & Garden

Plenty of Time for Managing
Crabgrass in Lawns

April 2, 1998

Warm weather and rain have greened up most lawns in recent days. Crabgrass becomes a concern of many people as conditions warm in the Spring. There are a variety of ways to manage crabgrass in lawns, and there is still plenty of time to consider your options.

Crabgrass has an annual life cycle, which means any crabgrass present in lawns in 1997 is dead, and the only way for crabgrass to appear in 1998 is by seeds germinating into new plants. Crabgrass seed will start to germinate when soil temperatures get close to 60 degrees F and stay there for several consecutive days. Crabgrass likes full sun, thinner lawns, and frequent watering.

Keeping those preferences in mind, adjustments in lawn care practices can have a major impact on reducing the chances of crabgrass appearing in your lawn. Mowing height is a major one. Mow between 2-1/2 and 3 inches and there will be fewer crabgrass plants in your lawn. Light, frequent watering of lawns also favors crabgrass, so follow the general rule of deep, infrequent watering for your lawn. Crabgrass often invades areas seeded in late spring because of bare soil, frequent watering, and onset of hot weather which is ideal for growth.

Preemergence herbicides (weed killers) can also be used in spring for crabgrass control. These need to be applied to the lawn before crabgrass germinates. Late April into early May is the suggested time for applying preemergence crabgrass herbicide in northern Illinois. If April is unusually warm , apply by late April; otherwise early May is not too late.

Most preemergence crabgrass herbicides are found as a combination with lawn fertilizer at garden supply stores, so the crabgrass prevention and spring fertilization can be done at the same time. Follow the rates given on the bag.

One of the management problems associated with preemergence herbicides is seeding or overseeding practices. With the exception of a herbicide called siduron, all preemergence annual grass weed killers will also damage germinating desirable grass seed. Siduron may be found as lawn starter fertilizer with crabgrass preventer.


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