Historically, the transition process from overseeded ryegrass to the understory bermudagrass is one of the worst times of year for golf courses in the Southwest. The transition process can be deflating for superintendents due to thin bermudagrass cover and the need for sodding or sprigging certain areas once the ryegrass dies in the early summer months.
The good news is many courses have proven that a more proactive transition strategy works much better than historical methods that either rely on the onset of heat to remove the ryegrass or wait too long to apply chemicals that kill the overseeded rye. A real jewel has emerged in the form of an excellent chemical strategy.
While the “transition chemicals” have been used for over a decade, two chemicals have emerged as the frontrunners for a more successful transition process. Either penoxsulam or pinoxaden can be used to slow ryegrass growth and slowly shift the competitive advantage to the understory bermudagrass. Using penoxsulam at low rates, applied from late February at 4-6 ounces per acre to early April at 8 ounces per acre, slows ryegrass growth without any noticeable, rapid decline in turf color or quality of the playing surface. Similar results have been observed using pinoxaden with initial applications at rates from 0.5-2 ounces per acre beginning as early as the third week of February. Sequential applications continue on two- to three-week intervals at similar rates and may include up to four applications, but often only two or three are necessary.
This strategy slows ryegrass growth during the greenup phase for bermudagrass, which is a critical time to increase sunlight exposure on new bermudagrass leaves. The early spring chemical applications function like a growth regulator, thus decreasing mowing requirements at a time when ryegrass is typically growing very aggressively. The slower growth rate allows for nitrogen application – often beginning in April – to encourage bermudagrass recovery.
Courses using this method report the turf population has shifted to primarily bermudagrass by the end of April or early May in some cases. Neither of these chemicals control Poa annua and therefore a “cleanup” application with a chemical such as pronamide is often made to finally remove all the remaining cool-season grasses, if necessary.
While the transition process is never completely seamless, using these chemicals at low rates early in the spring is the next best thing. Best wishes during the 2021 transition season and please do not hesitate to contact a USGA agronomist in the West Region for more information on these strategies or any other agronomic practices.
West Region Agronomists:
Brian Whitlark, senior consulting agronomist – bwhitlark@usga.org
Cory Isom, agronomist – cisom@usga.org