By Don Myers
What does it look like?
Crabgrass, a warm-season annual grass, has two common forms: smooth crabgrass and large, also known as hairy, crabgrass. Both forms of the weed are light green in the seedling stage, progressing to a dark green as true leaves.
Smooth crabgrass is aptly named that because of its sleek texture. The blade is 1/4 to 1/3 of an inch across and can get up to 6 inches long. However, even in a mowed lawn it is capable of infestation. Large crabgrass is hairy on the upper surface and sheath. Unmowed, it will grow to 2 feet tall and 3 inches across.
Host material and range
Poor turf density and heavy exposure to light, moisture and high temperatures are ideal catalysts for crabgrass to thrive. The weed is found in turfgrasses and landscapes across the United States. Crabgrass reproduces by seed germination, which can be exacerbated by aeration, animal activity, construction and drought cracks. Smooth crabgrass produces approximately 180,000 seeds per plant, and large crabgrass generates approximately 150,000. It usually starts growing near curbs and sidewalks, which tend to have warmer average temperatures.
Not only does crabgrass aggressively spread across the areas it infests, the weed grows faster than the surrounding desirable grasses. It forms patches on the lawn and can gather together to form clumps.
The stronger and denser your turfgrass is, the lower the chance of crabgrass infestation. Applying a preemergent herbicide as part of a preventive program will also reduce the risk. This should be done in April or May, prior to crabgrass germination.
Even after preventive measures, the weed can still appear in stressed areas or where the preemergent was application was missed. Sometimes crabgrass can be hand-pulled and mechanically removed. Once the weed has appeared, a single treatment of a postemergent herbicide can be applied on cool-season grasses at all growth stages of crabgrass during the summer. Crabgrass is more easily controlled prior to tilling.
What can you do?
Making sure to use proper mowing heights reduces the germination and establishment of crabgrass seeds. Fertilizing the turf when it is actively growing, not overwatering, and other good cultural practices are the best ways to decrease the chances of crabgrass infesting and spreading across a lawn. In addition, applying treatments at the right time of year is crucial.
Don Myers is product development manager — herbicides and plant growth regulators, Bayer Environmental Science. For more information, visit www.backedbybayer.com