As the trend continues for golf courses to forego overseeding bermudagrass greens, challenges such as cool-season grass weeds have become more prevalent. It is not uncommon for superintendents to see the presence of cool-season weeds such as ryegrass, Poa trivialis, Poa annua and even bentgrass during the first year the greens are not overseeded. Not only are these weeds unsightly they can also create inconsistent ball roll detracting from putting quality.
Although none of the following strategies are foolproof, a combination of these tactics will provide good to excellent weed control in non-overseeded bermudagrass putting greens:
- Depending on the severity of the problem, one of the sulfonylurea herbicides should be sprayed in the months of October, November and December on the entire green. The spray must not contact any overseeded areas.
- Apply at a medium rate. For example, one superintendent commented he sprays three sequential applications of foramsulfuron at 0.4 ounces per 1000 square feet. Always apply according to label directions.
- Use a spreader/sticker to expedite drying and avoid run off.
- A boom sprayer can be used on a majority of the green, begin spraying three to four feet inside of the green and stop spraying three to four feet before the collar.
- For the greens perimeter, use a 25 gallon sprayer and apply by hand. It is important to calibrate using the same personnel and equipment that will be used for the actual spraying.
- Do not water the evening of the application.
- Use tracker dye and check the greens with a white towel the next morning, especially if dew is present. If the towel shows tracker dye the following morning, apply 2-3 minutes of irrigation and continue this practice for several days.
- Spray ahead of golfers and ideally leave a 2.5 – 3 hour gap between the sprayer and golf traffic.
- Do not mow or roll the morning after the application is made. The less traffic in the morning the better.
- Given the slow activity of the sulfonylurea herbicides during periods of cold weather, application during this time will leave golfers wondering what is wrong. In this case, consider utilizing a weed dabber filled with an appropriate mixture of diquat and non-ionic surfactant. The diquat may not kill the weeds but will burn the leaves and has relatively fast activity in cold weather.
- Depending on the weed density, the best method to use during cold weather is hand picking. It is amazing how many weeds can be removed by hand by four or five staff members equipped with sharp knives. It is labor intensive, but likely well worth the effort on the most important area of the golf course.
Above all, communicate to course officials and golfers that the removal of the cool-season weeds will be progressively more successful each year the greens are not overseeded. In many cases, the weed pressure is very slight the second year of not overseeding, assuming an integrated approach to controlling the weeds is employed.
For more information on cool-season weed control strategies or other agronomic advice, please do not hesitate to contact Pat Gross (pgross@usga.org) or Brian Whitlark (bwhitlark@usga.org ) at the Green Section Southwestern Regional Office at 714-542-5766.