Whether turf is dormant or not, applying a nonselective herbicide like glyphosate to turfgrass is always a little nerve-wracking. During the late winter months, USGA agronomists are frequently asked, “When is it no longer safe to apply glyphosate to dormant bermudagrass?” The simple answer is that as long as bermudagrass is dormant, glyphosate can be safely applied. However, there are a few things to consider before making an application.
First, confirm that the bermudagrass is completely dormant. Applying nonselective herbicides to emerging bermudagrass could result in delayed greenup or turf damage. In the Northeast Region, it is usually safe for superintendents to apply glyphosate to bermudagrass until early to mid-March, depending upon the weather. Using the appropriate carrier volume is critical to reduce the risk of turf injury. In the case of glyphosate, it is more effective at low carrier volumes—e.g., 20 gallons of water per acre. In conjunction with low volumes, use a fine-mist nozzle so that the product remains on the leaves and does not penetrate the leaf canopy to the growing parts of the plant.
Next, consider the potential for resistance. Some golf course superintendents are wondering if they have Poa annua populations that are resistant to one or more commonly used herbicides. To reduce resistance potential, apply a tank mix of glyphosate combined with a sulfonylurea herbicide. Almost all sulfonylurea herbicides are active on Poa annua, so many affordable products are an effective control option. Rotating mode of action (MOA) will also help reduce resistance potential. Be aware that simply using a different brand of herbicide may not change the MOA.
If a winter application of a nonselective herbicide makes you nervous, a late summer preemergence program is another option for winter weed control. There are many products to choose from, but they are not equally effective. Some products reportedly inhibit bermudagrass root development while others should not be applied to sandy sites. Carefully read every label before making any application.
Controlling weeds, in particular Poa annua, can be frustrating. However, with a sound program that rotates herbicide MOA and uses proper timing, successful weed management is possible. If you have additional questions, do not hesitate to contact a USGA agronomist in your region.
Northeast Region Agronomists:
David A. Oatis, regional director – firstname.lastname@example.org
Adam Moeller, director, Green Section Education – email@example.com
James E. Skorulski, agronomist – firstname.lastname@example.org
Elliott Dowling, agronomist – email@example.com
Addison Barden, agronomist – firstname.lastname@example.org
Paul Jacobs, agronomist – email@example.com