Poa Annua Seedheads
As Spring approaches, Course Managers are facing an old nemesis: Poa annua seedheads. The numerous seedheads that pop up continually at cutting heights below 3mm are amazing in themselves. However, annoyed golfers find seedheads to be disruptive to the uniformity of putting green and aesthetics by creating a silvery sheen to the surface.
Fighting Poa annua seedheads can be very challenging. Several researchers have dedicated years studying possibilities of improving the common inhibiting practices and there are important factors that turf managers should pay attention to when developing the best seedhead suppression methodology for their golf courses.
Ethephon is the only plant growth regulator on the market that has been proven to consistently suppress Poa annua seed heads on golf course turf. The effectiveness of the product, though, depends on several elements, beginning with the plant absorption
The flag leaf is generally the most metabolically active leaf in Poa annua and is also the primary source of energy for inflorescence. Experiments have shown that the flag leaf provides the greatest level of ethephon distribution to the inflorescence. Ethephon absorbed at lower leaves appears to have limited translocation and may explain reductions inefficacy. For this reason, it has been recommended that mowing should be avoided 24 hours after ethephon application.
The number of, and proper timing of applications are also responsible for seedhead inhibition. Research has shown that when a late Autumn application was included with a normal Spring programme, seedhead suppression was highly improved.
The actual advised management practices have become three applications of ethephon, starting with the first application in the Autumn, followed by one application in the Spring, and one application three weeks later. A relevant factor here in which Course Managers should be attentive to is in determining when the greatest percentage of Poa annua is in the “boot stage” as this is crucial for spring application timing. The first application should be made at cumulative 120GDD (Base = 6°C) for annual Poa biotype and 160GDD for perennial Poa biotype, noting that GDD should begin being accumulated around January 1st.
It is possible to use a free GDD app to determine the best time of application according to the increase in number of daylight hours in the days ahead. PGRs will not suppress seedheads after they have emerged and only then remedial practices such as vertical cutting can help diminish the problem.
A combination of ethephon with other products can also improve seedhead suppression and benefit turf quality. The industry standard mixture of ethephon +trinexapac-ethyl as well as ethephon + mono-and di-potassium salts of phosphorous acid, provides consistent seedhead control and improves turf quality over ethephon alone.
A plant growth regulator based on prohexadione calcium (27.5%) has been recently combined with ethephon in the Spring application and has shown better ethephon’s effectiveness because it delays seedhead production, which could buy time for ethephon to get into the plants and to the active site to inhibit. Also, the combination can result in less chlorosis or yellowing of turf.
Other than ethephon, trinexapac-ethyl and prohexadione calcium, a study published in2020 (Raudenbush Z, Elmore MT, Nangle E,Tuck DP.) has shown that mineral oil +ethephon tank mixture provided greater seedhead suppression than ethephon alone averaged across application timings.
Once seedheads have emerged on greens, cultural control through grooming or brushing is a good approach to remove seedheads and improve smoothness.
Brushing or grooming is also helpful in dislodging seed head and standing up leaf blades. Light brushing and grooming can be performed daily without damaging the turf. Grooming reels should beset just below the effective cutting height.
There are many reasons why Superintendents/ Course Managers will continue to fight Poa annua seedheads and keep annual it in the greens all over the world. After all, Poa annua competes well in wet, compacted, and highly trafficked areas, and is a very fast-growing grass, particularly when compared with many other types of golf course turfgrasses. Believe it or not, it is so easy to adapt, that it is the only known case of a successful invasion of an alien plant species in Antarctica (which scientists presume it will take them more than 10 years to manually remove). It also provides great playability. Proof of this is the Oakmont Country Club in Pennsylvania has pure Poa annua putting greens and has hosted more combined USGA and PGA championships than any other course in the United States.
Therefore, after reading the most up-to-date research on Poa annua seedhead suppression, I came upon something very interesting. Professor of Turfgrass Breeding and Genetics, David Huff and his team at Penn State University are aiming to breed Poa annua to produce seed for greens. And this may not take too long.
Should we start dreaming about a more resistant, firm, smooth and pure Poa annua surface that can actually produce less seed?
Maybe we should. Maybe it’s time!
Renata Mundim MS, Technical advisor to Turfgrass®
About the Author
Renata Mundim Ms
Technical Advisor To Turfgrass
Renata Mundim Ribeiro is a Biologist passionate about grass. She started her career in turf working as a research assistant at The Ohio State University. She has a Master’ s Degree in Horticulture and Crop Science and studied Golf Course Management, both at OSU. After working in agricultural marketing and teaching, she was chosen as one of the USGA Interns. Now, Renata works as an international speaker and specialises in developing education on turf health subjects.
Photo credits:
Poa annua seedhead – Source: Advanced Turf Solutions
Poa annua seedheads – Source: Bayer
Illustration is by Alec Kowalewski.
Graphic showing results of Autumn application – Source: Bayer
Poa annua seedheads – Source: USGA
Poa annua seedhead – Source: Advanced Turf Soluti
Oakmont Country Club – Source: USGA