The cure for what ails you

A weed is a plant we have not found a use for, says Robert Walker, professor of soils and agronomy at Auburn University. “There are a number of superintendents who have found a use for it and thus it is not a problem,” he says. “Most golfers have a mind-set of what a perfect turf is; uniform mono-stand with an excellent green color. Poa infestation is totally contrary to this mind-set; poor color, clumpy, disease susceptible, abundant flowers.” Hence, the ongoing efforts to eradicate Poa annua.

The battle waged by superintendents against Poa goes back almost as long as there have been golf courses. Commonly found in both cool-season and warm-season regions where it attacks turfgrass, Poa is difficult to control and seems immune to almost everything the well-armed superintendent throws at it. Chemical and cultural techniques work to some degree, but the insidious plant seems to simply rebound despite what is done.

Significant help may be on the way. According to Walker, Moghu Research Co. of South Korea has launched a new herbicide in that country for selective Poa control on bentgrass putting greens and fairways. It is a post-emergence-applied herbicide with some pre-emergence activity. It controls both perennial and annual biotypes of Poa. The common name of this herbicide is methiozolin.

“I first tested it in March 2009 at Auburn’s turfgrass research facility for Poa control in Crenshaw bentgrass and continue to evaluate it,” says Walker. “Methiozolin will be marketed in the US under the trade name PoaCure. My results with methiozolin for Poa control in bentgrass has been outstanding. Four to six applications at 0.5 lb ai/A has provided 95 to 100 percent control of perennial Poa on bentgrass greens, which have shown to have unbelievable tolerance to methiozolin. Drs. Shawn Askew at Virginia Tech and Jim Baird at University of California, Riverside, have obtained the same results with similar programs.”

Walker claims PoaCure will “revolutionize” Poa control on bentgrass putting greens. Additionally, Bermuda grass, zoysiagrass, Kentucky bluegrass and other turfs have displayed excellent tolerance to methiozolin.

“I have also demonstrated excellent control on Bermuda putting greens of ALS resistant Poa. Bentgrass is the current emphasis, but as ALS resistance increases it will become a valuable tool for warm-season grass managers.” Moghu Research’s goal is to have US labeling in 2015.

“This year I saw a putting green go from 20 percent bentgrass to about 50 to 60 percent bentgrass in a period of six weeks (six weekly applications),” says Aaron Hathaway, a researcher assistant at Michigan State University’s Hancock Turfgrass Research Center. “I never saw any bentgrass injury. I’m not sure about safety on other cool season turf grasses or warm season turf grasses just yet.”

Askew says methiozolin can be “a game changer,” adding, “It will be used on putting greens and other turf sites. Exciting things are happening with this compound across the country.”

Matt Shaffer, superintendent at Merion Golf Club in Ardmore, Pa., has been testing PoaCure and reports the product to be “amazing.” He adds, “It takes the Poa out very slowly. This way the putting surfaces aren’t compromised while the bent grass grows over the spots. I have used everything and done some pretty risky things to eliminate Poa. It wasn’t frustrating some of the time is was frustrating all the time. Some chemistries work well but they become less effective the longer you use them and the rates get so high it is cost prohibitive.”

Shaffer adds he hopes PoaCure ends up being a long-term solution for Poa control.

Askew also pointed to another product a potential valuable tool in a superintendent’s arsenal in the war against Poa annua.

“Xonerate (amicarbazone (Arytsta)) just hit the market. I don’t recommend it for greens but it is showing promise for green surrounds and fairways. Turf injury is weather and turf maturity dependent, but the product works well on Poa. It is best to get familiar with it before large scale use.”

“Amicarbazone is a promising new postemergence herbicide that is labeled for use in cool and warm season turf,” Hathaway says. “Amicarbazone is similar to other Poa-control products, like Velocity, in that it must be applied many times during the growing season and works best as application intervals are minimized (supply at seven-day intervals).”

Dr. Fred Yelverton, professor of crop science at North Carolina State University, points to products on the market and in the pipeline that can offer “some” help with Poa. But as with any new product, or one that a superintendent does not have experience with, he recommends that a product be tested on a nursery green or a practice green prior to taking it onto the golf course.

“The biggest issue going forward is going to be does a superintendent actually want to kill the Poa annua. This may sound odd but in my view this is a more important question than what product to use. We are to the point (or will be very shortly) where we can take out Poa annua in bentgrass. But the question is…do you really want that? If someone has 20 to 30 percent Poa annua in bentgrass, then the decision is easier and is more likely to be `yes.’ But if you have 70 to 80 percent Poa annua, then the answer is more likely `no.’”

As for enhanced cultural practices, Hathaway says Poa competes well in wet, compacted, and highly trafficked areas. Limiting nitrogen and water – especially in the heat of the summer – can give the advantage to other turfgrasses (bentgrass or Bermuda grass) as Poa does do well in these situations.

“There is always an ebb and flow in the advantage of one turf species over Poa. Bentgrasses (especially certain cultivars, like Penncross), for example, out-competes Poa in high heat and dryer years, while Poa gains the upper hand in cooler weather and wet periods. The key is to hit Poa hard when it is vulnerable (Velocity works best in the hottest part of the year) and to minimize the rise of Poa in the cool weather of the spring and fall.”

Traffic can’t easily be limited, but superintendents can concentrate on certain things like making putting greens bigger and moving pin placements consistently.

Matthew Sousek, University of Nebraska, Lincoln, plant science research technologist, has several suggestions to control Poa annua through cultural practices. Superintendents may want to raise mowing heights; limit fall nitrogen applications; keep turf dry; aerify in summer when germination is not favorable; avoid any fungicides that control anthracnose or summer patch; and limit application phosphorus, which promotes rooting of young plants (Poa) and seed head production.

Walker opines, “It’s all about preventing the introduction of seeds and/or preventing seed production. Anyone who has played golf when there is dew is on the grass has surely noticed Poa seeds clinging to the heels and soles of their shoes. As players move from course to course there is always a potential of introducing seeds.”

In the South, seeds are probably introduced in Poa trivialis, bentgrass and perhaps perennial ryegrass seeds. Purchasing quality seeds is a good step towards prevention. The best seed prevention is to control Poa on fairways, roughs, surrounds and tees with a dense competitive turf and supplement this with effective herbicides.

Says Walker “Poa invades thin, weak turf readily. Herbicide choices are much better for all areas of the course than putting greens.”

Says Sousek, “For some it is feasible to reduce Poa annua with the products on the market today, although it comes with a cost every year to prevent it from coming back. When stands of Poa annua are greater than 30 to 40 percent it may be best to do a complete renovation of the green and or live with the Poa and manage it to keep it alive. As of now it is impossible to completely eradicate the problem, rather we have to manage it so that it stays at acceptable levels at less than five to 10 percent, depending on the course’s tolerance level.”

Theoretically, having a Poa-free golf course will reduce the number and intensity of pesticide applications, hand-watering and other labor intensive efforts. The savings are balanced by the cost of Poa control, which is often substantial.

In climates where ice cover is a concern, having large percentages of Poa on the golf course could mean unplayable conditions and reestablishment of the turf if ice cover is more than 40 to 45 days. A Poa-free golf course will also allow for drier conditions since other grasses have deeper root systems and can tolerate surface dryness better than Poa.

Poa annua may be around forever. But the very near future may hold some exciting prospects for its control, if not eradication, when and where desired.

John Torsiello is a Torrington, Conn.-based freelance writer and a frequent GCI contributor.