© dr. Eric Reasor/PBi-Gordon

Goosegrass is on the loose. Or at least all the potential factors for more outbreaks are aligning — even in new places.

Once associated with warm-season growing environments, goosegrass challenges are becoming common in historically cool-season locations. Work in New Jersey, Pennsylvania, Illinois, Indiana, Ohio, Kansas, Missouri or Nebraska? Consider yourself warned.

Rutgers University weed extension specialist Dr. Matt Elmore says he’s spotted goosegrass as far north as New England. “In most of those cases there it hasn’t yet reached the status of being considered a primary weed target,” he adds. “But in New Jersey, it’s a primary weed issue for many golf courses and that’s true as you go south into the Mid-Atlantic and Philadelphia area.”

Work in the Southeast or epicenter of the Transition Zone? There goosegrass equals 10 of the dirtiest letters in weed control. “I give extension talks where I start out by saying, ‘Is goosegrass the new Poa?’” says Dr. Jim Brosnan, a professor in the plant sciences department at the University of Tennessee and director of the school’s Weed Diagnostics Center. “In this part of the world, yes, Poa is our No. 1 weed issue and that’s very, very resistance driven. I would contend that goosegrass might be No. 2. It has its own suite of resistance issues and our options for removal are really, really limited.”

Similar to crabgrass, goosegrass is an annual weed. But according to PBI-Gordon Southeast research scientist Dr. Eric Reasor, initial goosegrass germination can occur around a month later than crabgrass, when soil temperatures reach between 60 and 65 degrees. The plant dies at first frost, but seeds dropped in the fall will lead to infestations the following year. Goosegrass also features a different appearance than crabgrass.

“Crabgrass seedlings come to a point at the leaf tip and goosegrass is rounded at a very early stage,” Reasor says. “Then, as the plant grows and matures, goosegrass gets this real distinct white, silver color at the base of the plant where all the different tillers come off.”

Thin turf atop compacted soils mowed at low heights is susceptible to goosegrass growth. Think about what has occurred on most golf courses the past two years. More rounds. More cart and foot traffic. A formal research study on the golf surge of 2020-21 and weed outbreaks hasn’t been released, but consider the conditions goosegrass relishes — and the conditions these past two years — and keep an eye on cart entry and exit points and collars this summer.

“Goosegrass seems to grow well in compacted soils and if your soils are trafficked or compacted to the point where desirable turfgrass isn’t competitive and that turfgrass thins out, then the turf becomes susceptible,” Elmore says. “This includes areas where cart traffic becomes a problem, or walking traffic. We also typically see it on cleanup passes on putting greens, collars and those sorts of areas that aren’t necessarily more compacted than everything else but tend to thin out in summertime.”

© dr. Eric Reasor/PBi-Gordon

Goosegrass is also more apt to appear in high-traffic areas than crabgrass, Elmore adds.

Now that we have learned a few identification basics, let’s examine a perplexing topic: control. Consumer demands often mean raising mowing heights and restricting carts are impractical ways to limit emergence. As far as practical cultural controls, Reasor suggests considering “anything that can promote that turf competing against that goosegrass,” including additional aeration, nitrogen applications and hand watering in thin areas. “It’s not like spraying an herbicide, but you’re going to give that turf a better chance to compete against the goosegrass, which will, in turn, make the herbicide more effective.”

Elmore and the Rutgers team are conducting research on two components critical to establishing a preemergence herbicide program for goosegrass control: germination timing compared to crabgrass and herbicide resistance in cool-season turf. Rutgers research, Elmore says, has found incidences of dithiopyr-resistant goosegrass in cool-season turf.

“Many golf courses use dithiopyr and prodiamine as the foundation of their preemergence program for summer annual weed control and it works well for crabgrass,” Elmore says. “And, in the past, it worked well enough for goosegrass. What happened is that applying the same herbicide year after year allowed goosegrass to adapt. When the same thing is used year after year, nature usually finds its way around it.”

That resistance has resulted in cool-season courses turning to warm-season stalwart oxadiazon as a control tactic. Elmore recommends first-time, cool-season users of oxadiazon to target areas with previous severe goosegrass infestations and make just one application of the active ingredient during the first year of a program.

Preemergence herbicide resistance also represents an issue in the region where Brosnan studies goosegrass control. “We have prodiamine resistance in this region,” Brosnan says. “It has been documented for a long time.” Brosnan adds that research conducted by an Auburn University team led by Dr. Scott McElroy is examining oxadiazon resistance in warm-season turf.

Determining the difference between herbicide resistance and effectiveness when it comes to goosegrass control can be tricky. The fast and firm conditions promoted throughout the industry can result in producing environments lacking enough moisture for many postemergence herbicides to work as intended, according to Brosnan.

“The water gets a little muddied with how some environments goosegrass is found in aren’t that hospitable to herbicides working that well,” he says. “It becomes kind of blurry. Is this resistance or a function of trying to remove plans from a pretty harsh environment and the herbicide is not set up to succeed? This is why the research process, collecting plants, growing them out for seed, doing that classical work needed to confirm resistance under controlled conditions is really important.”

Postemergence control is an option on warm-season turf, although, Brosnan says, “we’re at a place where you might have to tolerate some turf injury to get goosegrass control effectively.” Elmore has studied tank mixes using different active ingredients for goosegrass control, including one with SpeedZone and Pylex, on non-bentgrass turf.

“You’re getting multiple modes of action and one of the things we also found is that you also don’t observe the bleaching on the goosegrass that you see with the Pylex alone,” he says. “Necrosis is much more rapid. Within a week, the plants are completely browned and necrotic, where if you have to apply Pylex on its own, we’re looking at white leaves seven to 14 days after application. The combination is an effective option for two reasons: 1, It makes the control more rapid and it’s slightly more effective than Pylex on its own; 2, It’s a multiple mode-of-action approach. It should help preserve these herbicides for the long term.”

And there are no indicators goosegrass on low-mowed turf supporting abundant traffic will be just a short-term issue. “It’s a weed that has shown it can adapt moreso than others,” Elmore says, “and we have to be mindful of that.”