Mowing Height Impacts Weed Populations

— Written By NC State Extension

As we prepare for warmer temperatures (hopefully), it is important to remember the advantages of maintaining a healthy, actively growing turf to help combat weeds. Smooth and large crabgrass (Digitaria spp.) are common annual grassy weeds in managed turf in North Carolina.

One of the simplest and most economical ways to ensure turfgrass species such as tall fescue remain healthy and actively growing throughout the growing season is to mow at the proper height and frequency. Many homeowners mow their lawn shorter than recommended. The close mowing may cause scalping and induce stress making it less able to compete with crabgrass and other weed species.

Field experiments were initiated at Lake Wheeler Turfgrass Field Lab in Raleigh, North Carolina to determine the effect of tall fescue mowing height on crabgrass incidence. Evaluated mowing heights included 1″, 2″, 3″, or 4″ and were initiated once soil temperatures reached an optimum for crabgrass emergence and trials were evaluated monthly for crabgrass incidence through September. By mid-September, 1″, 2″, 3″, or 4″ tall fescue mowing heights resulted in 95%, 48%, 13%, and 0% crabgrass cover, respectively. These data indicate maintaining tall fescue at the appropriate mowing height may culturally suppress crabgrass in tall fescue.

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