Overseeded ryegrass has often been the nemesis of a smooth transition to bermudagrass for desert golf courses. If the overseeded ryegrass is dense and continues to grow in the spring or early summer, there will inevitably be areas where the bermudagrass understory does not recover. Fortunately, golf course superintendents are very adaptable and are always investigating strategies to improve the transition process. I have learned from their willingness to experiment, and learned that managing ryegrass early in the spring is the best method to successfully transition from cool-season overseed to bermudagrass.
This is referred to as the Ryegrass Management System (RMS) and it’s not a method that kills the ryegrass abruptly. Instead, this approach regulates ryegrass growth and slowly encourages the understory bermudagrass back to life. The following is an explanation of the key components of the RMS program.
Chemical applications are used to slowly shift the advantage to the bermudagrass. The system involves spraying penoxsulam at 4-5 ounces per acre beginning in the last week of February or early March and continuing applications at the same rate on three-week intervals. At this low rate, it is unlikely that you will see any impact on playing conditions after two applications. However, you should notice a reduction in ryegrass growth. If you place a sheet of plywood down over a sprayed area to create a nontreated control plot, you will see a slight discoloration in the sprayed area compared to the control. Over the past five years, we have found that golfers never notice anything has been treated when applications are made throughout overseeded areas. Continue making applications until early to mid-May. By mid-May, the turfgrass population will have shifted to primarily bermudagrass. While it is always a good idea to try any new program in a small area of your course first, you can take comfort knowing that this practice is done at high-end public and private courses where there is no room for a reduction in course aesthetics and playability.
Mowing heights must be reduced on all overseeded ryegrass areas beginning in late January. Ideally, closely mown areas such as tees, fairways and approaches should be reduced down to a range between 0.300-0.350 inch. Rough areas should be reduced down to 1 inch. By early April, rough heights would ideally be lowered down to about 0.625 inch or less.
Irrigation reduction during the transition period delays bermudagrass recovery. Therefore, it is recommended to begin increasing irrigation in mid-to-late April, using moisture meters to evaluate conditions and set a threshold for what is too dry and too wet. Typically, we have found that minimum soil moisture content in the 30% to 35% range is adequate during the transition process. This minimum level is generalized over many courses with different soil types using 3-inch-long rods. A slightly different range may be necessary depending on local conditions and soil types, but the overarching message is to avoid prolonged dry conditions during the period when bermudagrass is recovering.
Nitrogen inputs after overseeding are typically around 2 or even 3 pounds of nitrogen per 1,000 square feet prior to early December. Courses should significantly back off nitrogen inputs during the winter and spring months to encourage transition. If possible, it is recommended to apply very little nitrogen from early February through mid-April. Beginning in mid-to-late April, it is recommended to increase nitrogen inputs to encourage the bermudagrass and plan to apply approximately 2 pounds of nitrogen per 1,000 square feet from mid-April through early June. By early June, you should have greater than 95% bermudagrass cover and therefore you can significantly cut back on nitrogen fertility for the remainder of the summer.
Courses interested in trying this RMS program may want to begin by experimenting at the practice facility or on par-3 fairways. However, given the widespread success of this program in Arizona, southern Nevada and in the Coachella Valley for multiple years, there is plenty of evidence to support deploying this system on all overseeded ryegrass areas once you are comfortable with the steps. Best wishes for a successful transition from ryegrass to bermudagrass and please do not hesitate to contact me should you have any questions or comments.
West Region Agronomists:
Brian Whitlark, senior consulting agronomist – bwhitlark@usga.org
Cory Isom, agronomist – cisom@usga.org