Crowding Out Poa

Interseeding these two bentgrass varieties proves an effective tool in the battle against annual bluegrass

Golf course superintendents are all too familiar with Poa annua and the increased management inputs associated with managing Poa annua compared to creeping bentgrass. Therefore, interseeding creeping bentgrass into Poa annua is a goal superintendents have tried to achieve for years, often ending in frustration.

As recent research suggests, interseeding is not as simple as throwing out any bentgrass cultivar seed, topdressing and expecting bentgrass to overrun Poa annua. Traditionally, a fall or spring date is preferred when seeding bentgrass. However, when interseeding bentgrass into an area with a high Poa annua seed bank, Jim Murphy and associates at Rutgers University (Murphy et al., 2005) noted a June seeding resulted in greater bentgrass coverage and less Poa annua compared to a September or October seeding. The researchers also noted using an improved cultivar, L-93, increased bentgrass coverage compared to an older variety, Penncross.

The Downriver Golf Course practice putting green was interseeded with T-1 and Alpha creeping bentgrass. Note the amount of dark green bentgrass compared to the lighter green Poa annua more than a year later.

Similarly, at Rutgers University, Murphy and colleagues (Henry et al., 2005) noted interseeding L-93 into a 100-percent Poa annua stand at the end of June provided about 70 percent coverage, while interseeding in mid-August resulted in about 15 percent coverage two years after seeding. Mid-summer seeding is an effective strategy as Poa annua, a winter annual, is least competitive because seed germination rate slows and nearly stops as soil temperatures approach 77 degrees Fahrenheit. However, bentgrass seedlings can germinate and grow through the warm summer months. Therefore, two key factors for successful interseeding include: (1) early- to mid-summer seeding and (2) using improved cultivars.

Research objectives

In a previous Turfgrass Trends article (Brede, 2006), it was reported that three months following interseeding in Post Falls, Idaho, with either T-1 or Alpha creeping bentgrass into a 100 percent Poa annua green, about one-third of the putting green was converted to bentgrass. (Jacklin Seed by Simplot released T-1 and Alpha creeping bentgrass in 2004.)

The breeding objective of these cultivars was to effectively compete with Poa annua, giving superintendents the upper hand when trying to convert Poa annua-based playing surfaces to creeping bentgrass (Brede, 2007).

To put these cultivars to the test, several interseeding trials were initiated in real-world environments on golf courses across the country in 2007. Specific objectives included evaluating: (1) best establishment techniques when interseeding T-1 or Alpha creeping bentgrass into a predominant Poa annua putting green and (2) best seeding rates when interseeding T-1 or Alpha creeping bentgrass into fairways.

Site descriptions

Establishment technique studies were conducted on practice putting greens. Sites included Downriver Golf Course and Esmeralda Golf Course (daily-fee courses) in Spokane, Wash. T-1 and Alpha were seeded in mid-July 2007 at a rate of 2 pounds per 1,000 square feet at both sites. Treatments included spiking, aerifying, vertical mowing, no surface disruption and an unseeded control.

Seeding rate studies were conducted on fairways. Sites included Bunker Hills Golf Course in Coon Rapids, Minn., (daily-fee) and Green Valley Country Club in Lafayette Hills, Pa. (private). Seeding rates at both sites were 0, 1, 2 or 4 pounds per 1,000 feet. At Bunker Hills and Green Valley, T-1 and Alpha were seeded on June 8 and Aug. 2, 2007. Plots were seeded using a TriWave 60-inch overseeder (Turfco Manufacturing Co., Minneapolis). For both studies, percent bentgrass establishment was evaluated.

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