New products help keep Poa annua at bay

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 many Kentucky bluegrass areas, as it dies out in summer months, resulting in discolored and bare spots on an otherwise deep green field of turfgrass. 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 has received attention because it may provide some answers.

Differences in Tenacity treatments on turfgrass plots are illustrated.

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.

Developing 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.” He notes that among the many commercial and experimental varieties, the one now named Rush did the best in Poa annua resistance.

Doug Brede discusses various turfgrass trials.

Rush received a rating of 7 to 8 on a scale of 1 to 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 offers help on seedlings

Although complete renovation of turfgrass sites sounds like an easy way to avoid Poa, it’s not all 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.

Syngenta’s Tenacity, with mesotrione as the active ingredient, 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, University of Illinois turf researcher, confirmed the effectiveness of mesotrione in removing creeping bentgrass from Kentucky bluegrass.

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

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

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.

Catastrophic loss due to Poa die out.

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

  • The best time to seed is late August through early September.
  • An application rate of 4 ounces per acre produced the best results.
  • The first application should be initiated within four weeks of seeding.
  • Two to three additional applications are recommended at weeks four, five and six.

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 turf stands to strictly bluegrass, and provide more assurance that Poa will not resurface.

Nancy Riggs is a freelance writer and has been covering the green industry for Turf for almost 20 years. She resides in Mt. Zion, Ill.