Seedhead counts in Poa annua greens

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Editor’s note: This research was funded by the United States Golf Association.

Annual bluegrass (Poa annua L.) seedhead production on putting greens results in a number of detrimental effects, including, but not limited to, reduced putting speed and consistency and compromised aesthetics (2, 3, 6). To provide a more consistent putting surface, golf course superintendents have used a number of cultural practices, such as verticutting, the application of herbicides to reduce annual bluegrass populations, and plant growth regulators to suppress seedhead flushes (8).

Research and repeated golf course applications over many years have shown that plant growth regulators such as Embark (mefluidide) and Proxy (ethephon, Bayer) provide the best reduction in seedhead production (1, 4, 5). After phytotoxicity was associated with Embark, it was taken off the market, leaving Proxy as the only plant growth regulator available for suppression of annual bluegrass seedhead production (6, 7). However, reports from golf course superintendents indicate that seedhead suppression with Proxy in the field has been inconsistent.

Recent research (7) has determined that Proxy absorption and transportation from the flag leaf or uppermost leaf of the culm, which encloses the seedhead during the boot stage, contribute to seedhead suppression more than absorption and transportation from the lower leaves. However, mowing, a critical practice on golf course putting greens, removes the flag leaf. Therefore, the research (7) would suggest that mowing before Proxy application would prevent optimal absorption, and mowing following application would prevent optimal transportation of the plant growth regulator.

Poa annua seedhead

Right: In annual bluegrass, Proxy absorption and transportation from the flag leaf has been shown to contribute more to seedhead suppression than the same activity by lower leaves of the plant. Illustration by Alec Kowalewski

When considering these recommendations and the importance of frequent mowing in relation to putting green performance, the current dilemma facing turfgrass managers is how long must mowing be delayed before and after Proxy applications for maximum seedhead suppression. Therefore, the objective of this research was to determine whether mowing delays before and after the application of Proxy will affect the seedhead suppression of annual bluegrass during the spring flush.

Materials and methods

Field research was conducted on an annual bluegrass putting green vegetatively established in 2004 at the Lewis-Brown Turf Farm, Corvallis, Ore., on a 12-inch (30.48-centimeter) layer of sand meeting USGA recommendations for putting green construction.

For all treatments, Proxy was applied at a rate of 5.0 fluid ounces/1,000 square feet (1.59 milliliters/square meter). Seedhead counts were done using a small piece of plywood with a circular cutout 4.0 inches (10.16 centimeters) in diameter. The plywood was gently tossed on the plots three times, and the seedheads showing in the hole were counted. The three subsamples were then averaged.

The putting green used for this research was mowed with a Jacobsen Eclipse walk-behind mower at 0.125 inch (3.175 millimeters) with clippings collected. The green received fertilizer applications every other week in the summer months and monthly in the fall and spring (total 4.5 pounds nitrogen/1,000 square feet [219.70 kilograms/hectare] annually). Primo MAXX (trinexapac-ethyl, Syngenta) was applied alone throughout the growing season at a rate of 0.1 fluid ounce/1,000 square feet (0.318 liter/hectare) every two weeks. The experimental area was aerified every spring and fall with a John Deere Aercore 800 — 2- × 2-inch (5- × 5-centimeter) spacing with 0.5-inch (1.27-centimeter) (inside diameter) hollow tines. Light and frequent sand topdressing applications were applied to the green throughout the growing season. Irrigation and hand watering were applied as needed during the summer months to provide healthy annual bluegrass.

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