As warm and relatively humid weather persists across the southwestern Unites States, the resurgence of bermudagrass is inevitable. If left unchecked, bermudagrass likely will outcompete young ryegrass at golf courses that are overseeding. As reported by AZMET at the Encanto station in Phoenix, Ariz., the fall of 2015 has been slightly warmer and more humid than the same time-period in 2014. So far, the last two fall seasons have been significantly warmer and more humid than previous years from 1988 to 2001. The trend for fall, at least over the past two years, is increased humidity and warmer nighttime temperatures, both of which favor bermudagrass growth and recovery from overseeding preparations.
Last year, courses that overseeded before the ideal date – i.e., approximately October 15 in southern Arizona, September 21 in southern Nevada or October 20 in the Coachella Valley – generally experienced poor overseed density and quality by early December. The bermudagrass competition was too vigorous for the emerging ryegrass to overcome. Given the recent weather conditions, it should be no surprise if bermudagrass aggressively regenerates this year.
Armed with the knowledge that conditions are ripe for a strong bermudagrass recovery, golf course superintendents should be prepared to use cultural practices and growth regulators to slow bermudagrass resurgence. Here are a few ideas to consider:
- Apply trinexapac-ethyl (Primo®) at 10-15 ounces per acre after mowing ryegrass once or twice. Follow up on a 2- to 3-week schedule until temperatures turn cold and growth slows considerably.
- Apply triclopyr (Turflon® Ester Ultra) at 8-12 ounces per acre on hybrid bermudagrass or 10-16 ounces per acre on common bermudagrass approximately 2 to 3 weeks following overseeding.
- Maintain moist conditions at the soil surface to avoid desiccating young, short-rooted ryegrass.
- Although not popular, maintain a cart-path-only policy for up to 3 to 4 weeks after opening the course after overseeding or restrict carts to nonoverseeded roughs.
- Maintain a high height of cut on fairways – e.g., between 0.625 and 0.750 inch – to encourage ryegrass rooting while shading bermudagrass.
- Use pigments to improve turf color
- Once the first frost occurs and bermudagrass loses its color, lower mowing heights on fairways to approximately 0.325 inch to cut the dormant bermudagrass leaves and stems. After mowing a couple times at a lower height, raise the mowing height to a range between 0.400 and 0.600 inch to allow the ryegrass to grow and hide the bermudagrass.
Ideally, overseeding is timed when bermudagrass growth slows due to cool nighttime temperatures below 75 degrees Fahrenheit and soil temperatures below 72 degrees Fahrenheit at a 4-inch depth but before the onset of weather cold enough to slow ryegrass germination and growth. Overseeding earlier than the ideal timing increases the potential for strong bermudagrass competition and requires more inputs like water, growth regulators and plant protectants. Overseeding several weeks after the ideal timing may result in longer germination time but will require substantially fewer inputs without increased competition from bermudagrass. Consider planning an overseeding date closer to the ideal timing to improve your probability for success.
West Region Agronomists:
Patrick J. Gross, regional director – firstname.lastname@example.org
Larry W. Gilhuly, agronomist – email@example.com
Brian S. Whitlark, agronomist – firstname.lastname@example.org
Blake Meentemeyer, agronomist – email@example.com