There’s a plant that stands up well to low heights of cut, high traffic and shade on golf courses. The plant is Poa annua, and superintendents put much effort into eliminating it after it shows up uninvited at their courses.
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“No one plants Poa, but everyone ends up with it,” says Ron Calhoun, an environmental turfgrass specialist for crop and soil sciences at Michigan State University, who recently spoke about the weed at the Ohio Turfgrass Conference in Columbus.
While it can work for some courses, there are several reasons why superintendents would want to remove Poa, or annual bluegrass. Fist, the name “annual bluegrass” is a misnomer, Calhoun says. For the most part, the plant is a perennial, sprouting up on cue each year. It’s also different from other types of weeds in terms of seed production. Poa establishes quicker than most other types of weeds found on the golf course.
Annual bluegrass is adapted for low heights of cut, compaction and shade, which is why it can be ubiquitous and difficult to eradicate.
“These characteristics would be good if they weren’t in a plant we didn’t like,” Calhoun says.
But don’t be quick to eliminate the Poa without first assessing the situation. Ponder these questions:
- What is your level of commitment?
- What is your timeline?
- What will it look like – are you prepared (emotionally) for seeing plants die?
- Could it be Poa is the best species for the situation?
“Sometimes what’s there is very well adapted,” Calhoun says, referencing older courses where Poa has existed for decades and has been managed successfully to look like any desired turfgrass variety.
If, after taking account all these considerations, a superintendent still thinks eliminating Poa would be the best move for the course, he should do so with the best possible conditions to achieve the best possible results. The common control strategies are preemergence, postemergence and sterilization.
“People have mostly abandoned preemergence control but it’s important in an exclusion program,” Calhoun says, explaining it can prevent overuse and resistance development to postemergent herbicides. It shouldn’t be used in the same year as a postemergence product, he adds.
One application is usually sufficient, and the best time to apply a preemergent herbicide in cool regions such as Ohio is between Aug. 1 and Sept. 10. If a second application is necessary, the best time to do so is between April 1 and May 1.
The only nontraumatic postemergent control lies in plant growth regulators, Calhoun says, naming paclobutrazol and flurprimidol as options. Poa can be reduced gradually with regular use of PGRs, he says.
Selective postemergent control can be difficult. Herbicides such as Velocity can be an option for tees and greens, but as the Poa dies, it can leave voids in the turf and overseeding is often necessary. Also, be aware that it can leave a “flash” of yellowish coloring in bentgrass around days six to 10, but it’s only temporary, Calhoun says. Currently, there’s no herbicide that’s labeled as safe and effective for greens.
August is the best time for postermergent practices, Calhoun says. He has seen Velocity’s effectiveness when used once or twice a week for six applications.
“The control goes up as the number of applications increases,” he says.
The most drastic approach to Poa control is fumigation or soil sterilization. Calhoun recommends this method only for course renovations. He also stresses that it reduces, but doesn’t eliminate, the soil seed bank.
Whatever the method, superintendents shouldn’t set up themselves for a surprise. They should be sure to not confuse Poa with the intended plant, as some superintendents have done. Otherwise, those few small patches you thought were Poa could be the only grass left after an application, Calhoun says.
“At least now you have something to mow,” he says.