Battling crabgrass is a constant struggle for lawn and landscape companies throughout the U.S. whether you’re dealing with warm- or cool-season grasses.
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The summer annual weeds germinate as the weather gets warmer and while a pre-emergent herbicide can stop them in their tracks, post-emergent products are a viable option as well. Warm weather and wet conditions in many parts of the country are facilitating crabgrass germination, and the rains reduce the efficacy of pre-emergent applications.
Crabgrass germinates at about 56 degrees, growing throughout the summer and setting seed in the fall. While the first hard frost of the fall or winter will destroy many plants, the seeds will pop up again the following year, so a pre-emergent is a good option in the spring to stop crabgrass before it starts. If you haven’t used a pre-emergent, or if the heavy summer rains have thwarted your efforts, post-emergents can save your customers’ lawns.
To find it fast, look in thinner or shorter grass areas since they warm up first, making it easier for crabgrass to take over, according to Michigan State University Extension. Look for plants with coarser and wider textured leaves that are lighter green than the turfgrass, and look for matted areas. “The color difference is especially pronounced in cool-season lawns,” says Dr. Jim Brosnan, associate professor of turf and ornamental science at the University of Tennessee in Knoxville. “Both smooth and large crabgrasses grow via stolons and thus can form mats within a lawn.”
The earlier you can treat it, the easier it will be to control because as it matures, more applications will be necessary. “Being aware of the growth stage and life cycle is important,” Brosnan says. “The larger plants grow in size, the harder they become to control.”
While MSMA is still allowed on golf courses, it’s no longer available for residential or commercial lawns. Quinclorac, fenoxaprop-ethyl and mesotrione are all effective options, MSU says. But beware that removing a mat of crabgrass will leave a bare spot in the lawn where other weeds will invade. “Once plants are removed, something needs to be done to introduce plant competition in these bare areas,” Brosnan says. “This is particularly true with annual weed species like crabgrass that produce an abundance of seed.”
Researchers are the University of Tennessee study options for crabgrass treatments every year, looking not only at new active ingredients, but also integrated approaches that can control the weeds in an environmentally friendly way. They’ve even come out with a new mobile app to help landscapers choose an herbicide at mobileweedmanual.com.