The Invasion

Think of Poa annua as that annoying uncle who comes to visit unexpectedly once per year: you know he’s coming. You can prepare for his arrival with distractions to hopefully minimize his stay. He’s familiar, yet he’s still hard to figure out.

Fighting Poa annua (commonly referred to as annual bluegrass) on putting greens – where it’s perennially an unwanted guest – is a battle many superintendents face each spring. Poa adapts faster in cool-season climates. Once this turf variety invades a club’s greens, it is difficult to get rid of. For the best success, superintendents can attack this unwanted intruder in the early spring before it germinates by spraying its seedheads with Plant Growth Regulators (PGRs). This inhibits, and limits, Poa’s production before it reaches the surface and spreads.

Sean McCue can relate to this perennial pest. The superintendent at the Country Club at Castle Pines in Colorado for the past 16 years says trying to prevent Poa annua from further encroaching into his putting surfaces is one of his biggest maintenance challenges. Castle Pines’ greens are made up of a 25-year-old Penncross bentgrass variety, which at 70 percent, is the dominate strain of turf; Poa makes up the remaining 30 percent.

Castle Pines’ members, who are privileged to play this Jack Nicklaus design near Denver, are very active. According to McCue, they play, on average, 26,000 rounds in an eight-month season. And, like all private golf club members, they expect the highest level of conditioning.

Over the years, superintendents have used different formulations of Embark (now known as Embark Turf and Ornamental) to inhibit Poa seedhead production. More recently, many superintendents have used the combination of Primo MAXX and Proxy with good results. For McCue, a combination of PGRs is the best way to keep Poa at bay and to improve the overall playability of greens. Throughout his career, the superintendent has relied on a variety of products.

“These products have ranged from pre- and post-emergent herbicides and an extensive use of PGRs such as TGR, Primo, Embark, Cutless and Proxy, all with varying degrees of success,” McCue says.

Regardless of the product he uses, McCue says proper timing of the applications is the key to successful Poa suppression. While many superintendents rely on, and have achieved great results by using growing degree days (see “Growing Degree Days (GDD) for Poa annua suppression”) to time their applications, McCue subscribes to a different maintenance model; this illustrates that, yet again, there is no single scientific solution in the battle against unwanted turf species.

“Phenological indicators work best for me,” McCue explains. “Our weather patterns in Colorado in the spring are unpredictable and unstable with huge temperature swings from day to day. That’s why I find growing degree days extremely inaccurate. If I were to follow this philosophy, I would miss my application window by a month or more. For me, the key is Forsythia bloom. I have found the timing of this has always been right on the money for our applications.”

A little further east, Eddie Roach, superintendent at the Jimmie Austin University of Oklahoma Golf Club, finds GDD a useful tool. At this semi-private course, he uses GDD to determine when to apply PGRs to suppress Poa’s seedhead development on his Penncross greens. In the past, while he’s used Primo, his preferred inputs are Trimmit and Legacy.

“The PGR program we use is pretty good,” he says. “Poa still pops up, but we also control it well by using general maintenance practices such as aggressive verticutting and top dressing, and core aeration to promote a good growing environment for the bentgrass.”

Embark Turf and Ornamental is one of the most common PGRs to combat Poa annua on putting greens. Gary Custis, certified professional agronomist and manager of field research and technical services at PBI Gordon, explains that the product prevents the seedhead from forming – stopping it right in the crown area of the plant. Like all PGRs, getting the timing right is critical. Most superintendents will do two applications, depending on the seed head development. “Once you miss it, you’ve missed it,” he says.

No matter what PGR combination you use, or when you spray them, when it comes to battling Poa on greens, superintendents must prepare for a never-ending fight. Even the academics admit that what makes keeping Poa at bay so challenging is its aggressiveness. And, once it presents itself, it is much harder to get rid of.

“It’s one that, in all likelihood, will not be won,” says McCue. “You will need to do all that you can from an economical and physical standpoint to keep the Poa under control. This can be accomplished by sound agronomic practices that do not favor tipping the scale in the direction of the Poa. These include proper fertility, irrigation practices, timing of aerification, mowing heights and the use of PGRs and herbicides as an overall management strategy.

“The superintendent’s best friend against Poa annua invasion is to follow the Turf 101 principle of MTDT – Maintain Thick Dense Turf. This gives you the best chance of winning the war,” he says.

David McPherson is a Toronto-based freelance writer and frequent GCI contributor.

Web resources
For more information on Michigan State University’s research, see gddtracker.net. http://turf.unl.edu/ResearchReports/GreensPoacontrollnov2011.pdf

The USGA is partially funding a three-year research study at the University of Nebraska that is currently being done cooperatively with Purdue University and Michigan State University; the study is trying to find new and effective ways to control annual bluegrass on putting greens. This is a three-year study that will concludes after the spring observation in 2013.