Two New Poa Annua Control Tools

By Nancy Riggs

Kentucky bluegrass is one of the top choices for golf course fairways and athletic fields in northern climates. Its favorable attributes include aggressive rhizome growth and quick recovery from damage. Add to that its beautiful, lush green appearance, and it’s easy to see why it is a favorite among superintendents.

The South Side Country Club golf course boasts a high-quality Kentucky bluegrass stand after 10 years of overseeding.
Photos courtesy of Doug Brede, Jacklin Seeds, unless otherwise noted.

Poa annua has a long history of invading bluegrass, and the more intense turf management became by the 1950s, the more Poa annua became a problem. For nearly a half century, Poa annua management has taken center stage in the lives of many turfgrass managers. It is particularly troublesome on Kentucky bluegrass golf courses as it dies out in summer months, resulting in discolored and bare spots on an otherwise deep green field of turfgrass.

Doug Brede discusses various turfgrass trials.

Overseeding and the use of various herbicides have been the primary approaches taken with varying degrees of success in Kentucky bluegrass and ryegrass turf. Iowa State University’s work on genetically modified, or Roundup-ready, grasses may be key to finding some answes and, thus, has received a lot of attention.

Technology has been a major player in the development of two new products to help turf managers renovate or establish Kentucky bluegrass and reduce or nearly eliminate Poa annua invasion. Jacklin Seed’s Rush variety of Kentucky bluegrass was bred especially for its ability to resist Poa annua invasion. Tenacity, from Syngenta, can help turfgrass managers avoid and manage Poa annua. Doug Brede, Jacklin Seed research director and turf breeder, and Christian Baldwin, Simplot research specialist, recently discussed these two advances in technology.

Brede said, “We’ve brought most of the Poa problems on ourselves.” With bluegrass and fescues the traditional grasses found on courses prior to 1940, managing turf was a less conflicted undertaking. Bluegrasses and fescues exhibited deep, strong roots, producing vigorous plants. Frequent watering in small amounts wasn’t needed and was actually detrimental to the plants.

Following World War II, golfers began insisting on short cuts. With closer cutting and frequent watering, Poa annua was able to establish itself further and continues to haunt turf managers as they combat its growth. Various methods that continue to be incorporated into turf management programs include herbicide use and overseeding or complete turf renovation. Success with herbicide use has varied, and overseeding is a lengthy and cumbersome process despite its success in some cases. Even complete renovation hasn’t provided an answer as the Poa annua seed bank can remain in the soil.

Christian Baldwin discusses the effectiveness of Tenacity to inhibit Poa on newly seeded Kentucky bluegrass.
Photo courtesy of Christian Baldwin, Simplot.

A Poa-resistant variety

Rush, a new variety of Kentucky bluegrass from Jacklin Seed, was bred especially for its ability to resist Poa annua invasion, and to actually overtake it. Its existence, though, developed somewhat by accident. Brede followed his experimental variety rather reluctantly after discovering it among plots of experimental grasses that had purposely been overwatered during trials. “I was touring an astute Canadian distributor across a set of 2,500 Kentucky bluegrass turf plots here in Idaho,” Brede said. “There before us, among a sea of Poa annua, was a singular plot with little or no Poa. I was dumbfounded and a little embarrassed I hadn’t noticed it earlier.

“There’s a one in 1,000 chance that one variety will make it through the rigors of varietal testing,” Brede said. Although a long shot, Brede pursued the experimental variety following the distributor’s insistence. He said, “Amazingly, the experimental variety did pass all its exams and became a phenomenon among bluegrasses.” Brede said that among the many commercial and experimental varieties, the one now named Rush did the best in Poa annua resistance.

Rush received a rating of 7-8 on a scale of 1-9 in a green-up shortly after Idaho snowmelt. “That’s probably how Rush keeps Poa annua at bay,” Brede said. “It actively grows during the cold months of the year when Poa normally has the advantage.”

Brede added, “In a drought, Rush even outscored Texas Hybrid bluegrass and many other varieties.” Rush produces an increased level of thatch that appears to provide increased protection against Poa infestation. It appears that the thatch layer provides a covering that prevents Poa seed from reaching the soil where it can germinate.

New chemistry helps seedlings

Although complete renovation of turfgrass sites sounds like an easy way to avoid Poa, it’s not that easy. Turfgrass managers often find that the seed bank of Poa annua remains in the soil and surfaces the following spring after a great fall stand of Kentucky bluegrass has been observed.

The Rush variety of Kentucky bluegrass appears Poa free. Catastrophic loss due to Poa die out.

Tenacity, from Syngenta, features mesotrione as the active ingredient. It inhibits the enzyme that is required for carotenoid synthesis. Carotenoids protect the plant from excessive sunlight, and the shoot tissue turns white. Tenacity does not injure the new seedlings, and previous work has proved that Tenacity is effective in removing creeping bentgrass with multiple applications. Extensive work by Bruce Branham, turf researcher, University of Illinois, confirmed the effectiveness of mesotrione in removing creeping bentgrass from Kentucky bluegrass.

Differences in Tenacity treatments on turfgrass plots are illustrated.
Photo courtesy of Christian Baldwin, Simplot.

Tenacity has recently been labeled to allow its use on golf courses, athletic fields, sod farms, parks, commercial areas and home lawns.

A recent study was conducted by Baldwin to confirm the effectiveness of Tenacity in Poa annua control to provide recommendations for Kentucky bluegrass renovation on soil with a Poa annua seed bank. Rush and Award varieties of Kentucky bluegrass were seeded in September 2009 after the existing stand of primarily Poa annua was sprayed with glyphosate. Once established, the cultivars were mowed three times weekly at .5 inch.

Baldwin said, “We found that frequent applications at lower product rates provided better Poa annua control compared to higher application rates with fewer applications. The study found that no additional benefit in Poa annua control was obtained when Tenacity was applied on the day of seeding compared to the initial application four weeks after seeding.

“Results from this research project are encouraging in that Poa annua control is possible when renovating to Kentucky bluegrass,” Baldwin said.

Baldwin noted the following recommendations on the use of Tenacity in Kentucky bluegrass renovations based on his research.

The Poa annua-resistant variety of Kentucky bluegrass and the new chemistry employed in Tenacity give turfgrass managers new options that will shorten the time of converting their bluegrass-Poa courses to strictly bluegrass, and provide more assurance that Poa will not resurface.

Traditional overseeding success

Overseeding has been a traditional method to try to reduce the amount of Poa on golf courses and athletic fields. John Tonsor, golf course superintendent at South Side Country Club, Decatur, Ill., took a traditional overseeding approach to manage Poa on his course. Starting about 10 years ago, Tonzer began overseeding. He has continued the process with a high degree of success. The bluegrass stands on his fairways are excellent, but a decade of patience and intensive aeration and overseeding was required.

Tonsor has been superintendent at the South Side course for 32 years. He cited the lowering of fairway heights at the central Illinois golf course over the years. About 10 years ago, he began seeding low-mow Kentucky bluegrasses into his primarily rye and Poa course in conjunction with aeration .

Mark Grundman, left, Jacklin Seed turf specialist, discusses overseeding progress with John Tonsor.

“We used a variety of Jacklin Seed Kentucky bluegrass blends,” Tonsor said. “ Blue Moon, Nublue, Rugby, Rambo, Blue Chip, Perfection and Everest were among the varieties we used. We might stay with one blend two or three years then use a different blend.”

He noted, “We made sure we had a good fertility program.”

Although pleased with the current quality of his Kentucky bluegrass fairways, Tonsor said, “Our Jacklin rep, Mark Grundman, told me about Rush, and it sounds very interesting.”

Nancy Riggs is a freelance writer and frequent contributor. She resides in Mt. Zion, Ill.