After a warm December, January and February have felt more like winter in the Southeast, with multiple nights of below-average low temperatures. With the cold weather, golf courses in parts of the region are experiencing frost delays and bermudagrass putting greens have been covered on some nights. Frozen ground and low temperatures may present challenges in getting the course open for play, but they also provide opportunities for weed control, including applying nonselective herbicides for Poa annua control in dormant, non-overseeded bermudagrass.
There are many challenges associated with Poa annua control in bermudagrass, including herbicide resistance. Nonselective herbicides are a way to rotate modes of action and help prevent the onset of resistance. Depending on your location, February can be an ideal time to make these applications. When bermudagrass is fully dormant, nonselective herbicides – including glyphosate – can safely be used to control Poa annua and other winter weeds. The ideal time to make applications are days when air temperatures are above 60 degrees Fahrenheit, and after the bermudagrass is fully dormant. If one of these days presents itself, make sure to take advantage of the opportunity.
Keys to success
- Nonselective herbicides are just one tool for Poa annua control. Remain diligent with preemergence herbicides and cultural management programs to promote bermudagrass over Poa annua. There is confirmed resistance to glyphosate in some Poa annua populations, so it may not be a viable option at your golf course. If you suspect this is a problem, screen plants for herbicide resistance and, if confirmed, select alternative products.
- Make applications with a calibrated boom sprayer at 30 gallons per acre, or less, to keep glyphosate from penetrating deep into the bermudagrass canopy where living green stems may be present.
- Use a foam indicator, tracker dye or GPS-guided sprayer to ensure application accuracy.
- Use care when making applications around sensitive cool-season grasses like creeping bentgrass putting greens. Consider leaving a buffer strip near cool-season turf and using a safer product there, such as amicarbazone.
- Spray when air temperatures are above 60 degrees Fahrenheit. Research by Dr. Fred Yelverton of North Carolina State University has shown that glyphosate efficacy increases as air temperature increases. Days at or above 70 degrees Fahrenheit improve herbicide uptake by Poa annua.
- Apply glyphosate to Poa annua in dormant bermudagrass at 0.5 pound of active ingredient per acre. There are many trade names for products containing glyphosate, with various percentages of active ingredient, so confirm the glyphosate concentration in your preferred product before making application rate decisions.
- Make applications uniformly across the entire bermudagrass surface. You do not want to skip an area and miss small Poa annua plants that cannot easily be seen, or overlap an area and cause a delay in bermudagrass greenup.
- Glyphosate applications should be combined with a preemergence herbicide to extend Poa annua control and for early control of summer weeds. Combining pre and postemergence control strategies, rotating modes of action and using correct rates can reduce the risk of developing herbicide resistance.
- Take every opportunity available to control Poa annua. This weed is a legitimate concern at many courses in the Southeast, so don’t miss an opportunity to control it on dry, warm winter days after the bermudagrass is dormant.
If you would like to learn more about Poa annua control, please join the USGA and CGCSA for the Southeast Education Conference on March 14-15 at North Carolina State University. In addition to weed control, Dr. Yelverton and others will be providing insights into agronomic and labor issues along with many other challenges impacting courses in the Southeast.
Southeast Region Agronomists:
Chris Hartwiger, director, USGA Course Consulting Service – chartwiger@usga.org
Steve Kammerer, Ph.D., senior consulting agronomist – skammerer@usga.org
Jordan Booth, agronomist – jbooth@usga.org