Researchers work toward improving control

Poa annua, annual bluegrass, the bane of golf course superintendents around the world, is found in both warm and cool-season grasses. Highly managed turf is a special target location for Poa. Dr. A.J. Powell Jr., University of Kentucky (UK) turfgrass professor and researcher, and UK Plant and Soil Sciences colleagues are continuing to refine a program they began promoting several years ago (www.uky.edu/ag/ukturf). The program uses certain plant growth regulators (PGRs) to reduce Poa in bentgrass greens and fairways.

Photo courtesy of Steve Patton, UK College of Agriculture.
Dr. Powell discusses turf progress with Scott Bender, Griffin Gate Golf Course superintendent.

“When used correctly, the PGRs encourage the bentgrass to outcompete the Poa annua,” Powell said. “With lower percentages of Poa annua, the visual effects are less offensive.” Powell and superintendents using the recommended program emphasize that patience is the key in attempts to control Poa.

Powell has been studying Poa annua issues since 1963 when he was a graduate student at Virginia Tech. He said, “We’ve created some of our own problems with Poa annua with all the tender loving care we’ve given our bentgrass turf. Poa annua that has always infested short-mowed bentgrass has now become a tough perennial.

“When Dr. Paul Woosley was a graduate student here at UK, he conducted research on perennial Poa annua control,” Powell said. “He found that bentgrass and those perennial Poas were suppressed equally when using the PGR Primo. However, with Trimmit, Turf Enhancer or Cutless, the bentgrass growth was affected much less than the Poa growth. Thus, the bentgrass was allowed to outcompete the Poa.”

Differing Poa biotypes are present at one small site. Test plots at the University Club Golf Course illustrate differing results in treatment.

The UK program emphasizes spraying Trimmit, Cutless or Turf Enhancer every three weeks from spring through summer and fall. Powell said, “The reason we need to continue the program into the fall is that the Poa annua germination is at a maximum during the fall,” Powell said. “Young, germinating Poa seedlings will be greatly suppressed by these PGRs, and one does not have to use root-inhibiting preemergent herbicides.”

Poa control on courses

Jeff Benedict, University Club superintendent, manages two courses, Big Blue and Wildcat. He is using the program on greens at both courses and on Big Blue fairways, with Primo applied to Wildcat fairways.

Benedict has been at the course 18 years and has seen Poa increase in line with other courses in his region. He started using the program three years ago when Powell started research projects at various sites on the courses. Benedict uses Trimmit every three weeks, which he sprays in combination with fungicide and nitrogen when the timing works out. “We spray it together when we can, but if it’s not time for fungicide or nitrogen, we spray the Trimmit alone,” Benedict said. About 35 acres total are being treated with the program. Benedict has seen the most benefit on fairways with use of the Trimmit, which he attributes primarily to the higher cutting heights.

Idle Hour Country Club has significant Poa annua infestation that occurred following a renovation just before Ben Barnes came to Idle Hour as superintendent two years ago. Idle Hour fairways are about 40 percent perennial Poa. “Velocity treatment is just too risky because nobody knows just how much Poa annua is there,” Barnes said.

He used the UK program spraying Cutless last year April through September; this year, he plans to use it from the last spring frost to the first fall frost. He sprays 8 ounces of Cutless and 6 ounces of Primo every three weeks. “The program allows the bentgrass to overtake the Poa annua,” Barnes said. “Of course, you’ve got to have good fertility with your bentgrass growing well.”

Weather and regional climate differences play a major role in all turf issues. Slightly farther south, Jeff Kent is using the UK program at Quail Hollow Country Club in Charlotte, N.C. “Ben Barnes had moved to Kentucky, and he told me about Dr. Powell’s program,” Kent said. “His program targets the Poa annua at its weakest time in the summer months and at a time when bentgrass is aggressive.”

Kent used the program on a trial basis last year and began a full-fledged program this year just after finishing the Wachovia Championship this spring. He is using Trimmit in spring and fall, with Cutless during the summer months. “We water it in and include iron and fertilizer,” Kent said. “We’re seeing some thinning of the Poa already this year.”

“No researcher has a silver bullet,” Kent said. “You have to manage to your weakest link.” He noted that while Poa is not supposed to survive droughts, he has found it survives on greens even when they are exceptionally dried out for championship play. He emphasized that all management practices come into play. The superintendents agree that the more moderate winters in recent years favor Poa growth.

Looking back at Poa annua

Powell noted that Poa annua has been a significant problem for about as long as golf course greens and fairways have been around. “Golfers and everybody in the golf industry recognizes Poa annua in the spring because of the seedheads that form regardless of the height of cut.”

Poa is extremely susceptible to many diseases and requires special vertical mowing to maintain putting quality. Powell said, “Forty years ago, Poa normally died in summer when heat stress was maximum. With increased irrigation, better fungicides and nitrogen fertility management, Poa began to live as a perennial and dominated many golf courses. Once the perennial Poa becomes dominant, we most often must do our best to grow it rather than kill it. It has always had that love-hate relationship.”

Earlier attempts to eradicate Poa annua with herbicides were met with technical success, but the herbicides either injured the bentgrass or suddenly killed the Poa.

“Large dead Poa spots or browned-out bentgrass is not acceptable on today’s golf courses.” Powell said, “The only product we have now to take out Poa is Velocity. It continues to work well, but new bentgrass seed establishment must be accomplished quickly to replace ugly and dead Poa.”

Suppressing bentgrass flowering has always been an option to improve the visual and playing quality of Poa-infested turfgrass. Some PGRs control seedheads if applied during the spring, but others—like Primo, Trimmit, Turf Enhancer and Cutless—only delay seedhead development. One of the most significant issues with Poa is the high number of biotypes that exist even on a single golf green.

“It’s almost impossible to characterize the biotype or biotypes you have,” Powell said. Different biotypes flower at different times during the spring and for different durations, making the timing of applications extremely difficult.

Expanded research avenues

UK research has been conducted at the campus research farm and at various Lexington golf courses. “Field tests need to be on golf courses to encounter the many different Poa biotypes and management practices not on our agronomy farm,” Powell said.

“Poa annua is not as much of a problem in Kentucky bluegrass or other cool-season grasses because most of the Poa annua in Kentucky bluegrass is a true annual Poa,” Powell said. “With little irrigation, the Poa dies out in hot summers while taller-mowed grasses survive. A preemergent herbicide can be used to control Poa germination in the early fall.” Powell is concerned that more biotypes will evolve in the future and that PGRs will become less effective.

One method currently being investigated by UK researchers is a tank mix of Velocity and PGRs. Powell said, “This can be very effective if one begins this program prior to Poa becoming dominant and even when Poa is barely evident. That will be the hope for the future.”

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