Our favorite villain

Features - Pest & Disease

No matter what superintendents throw at it, Poa annua just keeps fighting back. But opinions on it, like the plant itself, might be evolving.

January 14, 2019

It’s the perfect plant. You just have to figure out a way to make the management a little more economically and environmentally sustainable.” — Dr. Alec Kowalewski, Oregon State

Golf course turf managers could not ask for a better antagonist than Poa annua. Annual bluegrass is, at times, just another weed or the ideal putting surface, depending on climate. In terms of hardiness, it can come close to Terminator-levels of coming back, each time seemingly with a new resistance to whatever came closest to taking it out.

The superintendents treating it like a common weed are constantly looking for a better mousetrap, and those encouraging it on the course are always in need of support.

Superintendents are often eager to ask turf researchers about the newest mode of action to manage Poa, but approaches to working with one of turf’s best-known villains have started to shift. Turf researchers shared their origin stories about Poa, and how their views have evolved.

From a biology perspective, I don’t think we’ve unlocked it. I don’t think we have a great understanding of it, which is why it continues to be an area of active research. The vast majority of work still goes into ‘Who cares why it’s adapting? Let’s just control it.’ I think there’s lots of questions to be answered, and I don’t think a lot have.” — Dr. Scott McElroy, Auburn University

Unlocking secrets

Dr. Scott McElroy, professor at Auburn University, got his master’s degree working on Poa, but he didn’t go out of his way to seek it out as an undergrad. His advisor at the time told him that he would be working on it, and that was that.

“I really didn’t have any opinion. I thought, ‘This is a weed, this is research, this professor says he’ll pay me a stipend to work on this project,’” McElroy says. “It was really no more than that. And it’s come to really kind of define my career in many ways.”

Poa annua is the dominant grass varieties on greens in multiple regions, including the Pacific Northwest.
© tim cloninger/Eugene CC

When McElroy started studying one of most widely distributed plant species on the planet, he found a wealth of interesting sources of study, he says.

“My interests more reside in the diversity and genomics of it as a species, and why is it so prolific? What makes this species special that it can grow in Antarctica and then Orlando?” he says. “As a researcher you look for problems, and it’s a constant problem.”

McElroy still thinks of annual bluegrass as a weed, as there’s still a lot of call for control methods, but he’s also trying to convince those in the biology and research fields that Poa is worth taking notice of, not only in how it adapts to change, but also in how it has evolved over time.

Even with the amount of time he’s spent with Poa, McElroy thinks research hasn’t even started to really understand the plant.

“From a biology perspective, I don’t think we’ve unlocked it. I don’t think we have a great understanding of it, which is why it continues to be an area of active research,” he says. “The vast majority of work still goes into ‘Who cares why it’s adapting? Let’s just control it.’ I think there’s lots of questions to be answered, and I don’t think a lot have.

“It obviously has the ability to adapt and survive, either in managed or unmanaged ecosystems. So the question arises, why is that occurring? Is there something special about its species that allows it to adapt? And can we manipulate that in some way to stop it from invading?”

McElroy has lots of plans for future research, but one particular area he finds interesting is dealing with Poa via cultivation techniques. For example, using fraze mowing to remove the weed seedbank could help control its growth.

Another angle is looking at how resistance in Poa begins, whether it moves from different locations or starts fresh in each place, he says.

“If it’s jumping around, we can correlate these populations, and that tells us what that what we need to do is a better identification and containment type of management across a broader swath of geography,” he says. “Whereas if it’s arising de novo (anew) in each of these individual sites, then our emphasis should be on continued training of people to prevent the rise of new herbicide resistance in individual locations.”


Changing minds

Dr. Jim Brosnan, associate professor at the University of Tennessee, was surrounded by Poa when he went to Penn State for his undergrad work. At the time, he just thought of it as another type of turf. But he was intrigued when, during his first job as a faculty member at the University of Hawaii, he found Poa out on the islands.

“It was surprising to me. It wasn’t everywhere, but in different microclimates on different islands, particularly at elevation, you could see Poa in fairways,” he says. “That was kind of an eye-opener for me.”

But things really kicked up when he was on a 2010 USGA extension visit to a golf course in Tennessee, and a superintendent mentioned in passing that his Poa just wouldn’t die until the high heat of the summer kicked in.

“We turned around, went out there, I got cup cutters and sampled some plants, and went through the confirmation process of confirming that it was glyphosate-resistant,” he says. “At the time, that was only the second case of glyphosate resistance in turf.”

He began talking about the resistance in extension settings, and more and more superintendents came forward to ask him to check out their Poa for the same issue. And that has spurred almost a decade of research for him.

“It’s so multifaceted from a biology standpoint,” he says. “It’s just amazing, the adaptability of this species. Not only its adaptability to different microclimates, but also what we do management-wise, its ability to resist different modes of action and strategies.”

But what Poa has done most for Brosnan is offer a window into what turf programs miss as educators, he says. “We see this adaptability, and the solution that everyone wants to deal with that is something that comes out of a jug,” he adds. “We have enough data to know and indicators from other crops to know that that’s not the solution.”

The plant’s adaptability challenges educators to approach it from a human psychology perspective: Researchers know that if turf managers don’t diversify, treatment is just selecting for resistant populations, but that can sometimes mean passing over a quick herbicide fix.

For Brosnan, the best turf managers working with Poa are planning out two to three years, developing a program that bakes diversity of mode and active ingredients before resistance ever becomes a problem.

“We need to do more to change our approach as educators to help superintendents solve this problem, because the standard stuff we’re doing is clearly not working,” he says. “I’m giving talks about sitting down and building a plan to approach how you’re going to handle this weed, because it’s so adaptable. That is so far removed from our standard approach of, ‘Here’s this weed and here are the seven herbicides that work well on it.’”

To help build these plans, researchers just need more data on the biology of the weed to build effective, sustainable programs.

“Can we better model Poa germination, and have models of soil temperature, soil moisture and daylight, and daily light integral and day length? All of these meteorological parameters that are out there,” he says. “Can we use that to build a model to predict what this weed is going to do, so we can use the tools we have in the most effective way possible, by understanding the biology of the target?”


Joining In

When Dr. Alec Kowalewski, associate professor at Oregon State, started grad school at Michigan State University, annual bluegrass was considered a weed. That is, until a researcher called Joe Vargas helped start a change in how people thought about annual bluegrass in Michigan, he says.

Later moving to Oregon, Kowalewski saw the vast majority of the people living in the western half of the state treating annual bluegrass as the dominant putting green surface, he says. That climate gets enough precipitation without heavy snow in the winter, making an ideal environment for annual bluegrass to thrive. Annual bluegrass cuts a swath all the way down the Pacific Northwest coast to Monterey Bay in California. “In the classroom, I was taught it was a weed, but then the first golf course I worked on (in East Lansing, Mich.) was predominantly annual bluegrass putting greens,” he says. “I learned very quickly that there are things we learn in the textbooks and classrooms, but then as soon as we go out in the real world, it all changes and goes out the window.”

Annual bluegrass takes about 90 percent of his research, as a perennial biotype that is most susceptible to disease like microdochium patch for about six months of the year, he says. As one of the fewer researchers working toward building healthy stands of annual bluegrass, it’s changed his perspective on approaching it.

For instance, using lighter, more frequent irrigation helps annual bluegrass stay strong, and Kowalewski has taken that principle on to research home lawns, resulting in collective less use of water.

He’s also looking for ways to use pH to manage pathogens in annual bluegrass without using fungicides, as several West Coast regions have tight restrictions on pesticide use. One issue is that bringing the pH to a level that reduces disease activity can make conditions more favorable to creeping bentgrass, putting Poa in a vulnerable position that it’s typically not used to.

“So we’re trying to figure out the perfect balance of pH where it reduces disease activity but not promote creeping bentgrass,” Kowalewski says. “There’s tons of social pressure in the far western states to reduce pesticides. We’ve got golf courses in California that have to manage with no pesticides at all.”

But it’s a great plant for the environment of the western states, and golf course superintendents can turn its adaptability into a benefit by just keeping it happy, he says.

“It’s the perfect plant. You just have to figure out a way to make the management a little more economically and environmentally sustainable,” he says.

One downside to trying to work with Poa rather than against it is that it’s not commercially available, he says. Growing annual bluegrass in on a course means planting a fine fescue or creeping bentgrass, and then cranking up the fertilizer to push it toward annual bluegrass. “And then in about five years, you’ve converted it over to annual bluegrass,” Kowalewski says.

Seed companies say that the West Coast market is too much of a niche to make annual bluegrass seed sales worthwhile, not to mention that as an annual, Poa’s genetic diversity is very high, Kowalewski says. If a superintendent wants to get aggressive about building an annual bluegrass stand, collecting cores from another golf course might be the easiest way to go. But its trouble finding a place in the market doesn’t change his opinion of its usefulness on the golf course. “I think because you can’t go buy a bag of annual bluegrass, that’s the biggest deterrent to it,” he says.


Sharing knowledge

Dr. Jay McCurdy, assistant professor at Mississippi State University, looks at annual bluegrass from a global perspective. “It’s one of the most cosmopolitan grass weeds in the world,” he says. “It’s on every continent, including Antarctica.”

Growing up in west Tennessee, dealing with Poa was an ever-changing, moving target. His first experiences with it were just as a problem to be solved, and as resistance began to rise, he had to start putting his education to use to find new ways to approach it. But the root of the problem with Poa was something a little tougher to grasp, he says. “It’s existential to the way we think about weed control, because it’s a weed we can – I wouldn’t say ‘tolerate’ – but we can mow and play on it. It sucks, but we can do it,” McCurdy says.

But even working with other researchers and superintendents, there don’t seem to be any easy solutions to the problem, at least not without creating even more problems that take up more bandwidth, he adds.

“A lot of places, your entire year revolves around what applications you’re putting out for Poa,” McCurdy adds. “It is vertically integrated to the point that we put out a pre-emergent and a post, and then you’re putting out a growth regulator to manage seedhead production. There’s nothing else I deal with that’s like that.”

McCurdy is committing to spending even more time on annual bluegrass, working with a Poa project through a USDA specialty crops research initiative project bringing together about 16 universities to collect samples of annual bluegrass for study. The project (which can be found on Twitter @ResistPoa) shares those samples from states including Alabama, Tennessee, North and South Carolina, Virginia, and Texas to find new ways to manage Poa in new, sustainable ways, he says.

“That’s where this project is really headed,” McCurdy says. “It’s not about resistance, it’s about how we can best manipulate the environmental situation so that we can minimize the amount of Poa, then clean it up with herbicides if necessary.”

The project blends backgrounds and approaches in looking for solutions, going past an approach of chemistry alone, he says. But the project won’t make much headway without support from superintendents who supply samples. “We need people who are volunteering annual bluegrass populations that are resistant,” he says. “If they have them, we need them to get in contact with us.”

Kurt Kleinham is a contributing editor from Akron, Ohio.