The omnipresent weed

Consider crabgrass the anywhere, everywhere weed. North or South. East or West. Pick a turfgrass species or variety. Name a playing surface.

Anybody reading this article has likely encountered crabgrass on a golf course. Don’t feel bad. Sports field managers, landscape contractors, sod producers, homeowners and grounds employees in all sectors encounter crabgrass, too. “You hesitate to say it’s a cosmopolitan weed,” says NC State University assistant professor Dr. Travis Gannon, “but it’s prevalent across basically all turf sites. It’s more of an issue in some sites than others.”

Crabgrass can hurt playability and aesthetics during key parts of the golf season. “It’s the earliest summer annual grass to germinate and emerge as well,” Gannon adds. That timing coincides with tournaments and tourism periods at warm-season courses and the shift to peak-season green fees at cool-weather courses. Unsightly playing surfaces at the wrong times drive potential business elsewhere.

Soil temperatures are an indication that crabgrass is ready to appear. The “textbook definition” of conditions required for crabgrass emergence, according to PBI-Gordon Southeast scientist Dr. Eric Reasor, includes three to five days of mean soil temperatures of 55 degrees and above. By comparison, goosegrass emergence occurs when soil temperatures reach between 60 and 65 degrees.

Visual hints of crabgrass emergence also exist. Reasor suggests observing the flowers around you to determine the commencement of crabgrass season. “Daffodils are early emergers,” he says. “When you see them, that’s an indication that, ‘Hey, things are starting to wake up out there.’” If daffodils aren’t found in your neighborhood or course, monitor areas around cart paths, south-facing slopes and large, bare areas that receive abundant sunlight. Forsythia blooms are another indicator that crabgrass emergence is imminent.

Crabgrass and goosegrass resemble each other early in germination. As crabgrass matures, it develops a fatter, wider leaf blade than goosegrass and other weeds, according to Gannon. Crabgrass competes intensely with desirable turf varieties for surface space. And that competition varies depending on turf species and variety.

“Because crabgrass is a summer annual, it’s going to thrive in heat, whereas bentgrass, ryegrass and fescue don’t thrive as much in heat,” Reasor says. “You might not get that turf competition in the North that you get in the South with Bermudagrass and zoysiagrass, where it’s growing like crazy. That turf can compete better against crabgrass. But that’s not to say crabgrass is not a problem down South. The warm-season turf can just fill voids quicker than if you have bentgrass in July in New Jersey, where it might not recover as quickly and it can lead to more crabgrass.”

How crabgrass is controlled has changed significantly in Gannon’s 23 years at NC State. “When I first started here in this region, you could historically get by with a single application of a preemergence herbicide,” he says. “Due to a number of factors, including application history as well as the longer growing season that we have now, you can’t just get by with a single application today.” Gannon recommends split applications six to eight weeks apart for control.

The region where Gannon conducts research is relatable to thousands of superintendents, because North Carolina supports courses with warm- and cool-season turf. Soil temperatures lead to preemergence herbicide applications being made as early as February in some regions. Reasor, who is based in the Dallas-Fort Worth Metroplex, sees varying growing environments on courses he visits, yet he notices commonalities among solid crabgrass control programs.

For starters, effective programs nail the initial preemergence application. “That timing is really important,” Reasor says. “You don’t want to be too early where that herbicide control will run out and you get a lot of emergence. But you don’t want to be too late where you get it out after it emerges.”

Proper sprayer calibration and applications conditions are other factors to consider. “One of the biggest things I have seen — and it’s not just on crabgrass, it’s on a lot of weeds — is applying in dry conditions can really impact control,” Reasor adds. “Make sure the turf isn’t under drought stress, because if the turf is under drought stress, it’s likely the weed is under drought stress and you need those weeds to be growing so they can actively use, absorb and uptake that herbicide.”

Fewer herbicide resistance concerns surround crabgrass than goosegrass or Poa annua, and multiple postemergence herbicide options provide control, including PBI-Gordon’s Q4 Plus Herbicide. Reasor uses an analogy to the human lifespan to describe postemergence crabgrass control.

“There are two different stages of crabgrass where you can get the best control: early stages and very mature stages,” Reasor says. “The teenage years of crabgrass, when it’s really growing, makes post-emergent control really difficult. If you do need to apply a postemergence or a postemergence is your sole strategy, make sure it goes back to watching the emergence, looking for those seedling poppings and applying the herbicide sooner rather than later. A lot of these herbicides require a two-application program. Make sure you have that in mind going into it. A lot of those postemergence herbicides don’t last in the soil like the preemergence herbicides do.”

The annual crabgrass tussle ends at first frost. It then repeats itself the following season at a time to be determined. “We like to talk about a calendar timeframe,” Gannon says, “but every year and every season is different.”

Guy Cipriano is Golf Course Industry’s editor-in-chief.