Annual bluegrass is an amazing plant. Its presence on all seven continents tells you all you need to know about its ability to adapt. One characteristic that makes it such a ubiquitous grass is its prolific seed production, with a single plant capable of producing over 2,000 seeds (Mitich, 1998). Unfortunately, those seeds can be a big headache for superintendents with annual bluegrass in their putting greens. When developing a strategy for managing seedheads it’s important to consider your overall goal with annual bluegrass, to stay up to date with research and to try new things if you’re not getting the results you want.
Keep in mind, suppressing seedheads strengthens the plant by allowing it to conserve energy it would otherwise use to reproduce. If you’re trying to eradicate annual bluegrass from your greens with herbicides or plant growth regulators (PGRs), suppressing seedheads may run counter to those efforts. However, letting the seedheads emerge creates a number of potential problems, so it can be a tricky decision.
Two or three sequential applications of the PGR ethephon is the go-to strategy for seedhead suppression and typically marks the start of the growing season in the Northeast. However, many turf managers have taken notice of the winter ethephon application research spearheaded by Dr. Shawn Askew (2017) and now make their initial spray early in winter to improve results. Tank mixing trinexapac-ethyl in follow-up applications in the spring may help reduce turf discoloration and improve seedhead suppression.
Application timing can vary a lot from year to year and between locations, so some superintendents use a growing degree-day model or websites that track seedhead emergence. Another tried-and-true method is to scout for plants that have initiated seedhead formation inside the stem, known as the boot stage. Although it can take some practice, this technique will give you site-specific information and let you know exactly when it’s time to make your first spray. Phenological indicators like the onset of forsythia bloom have long been used as well.
Although ethephon is an effective product, when the widely used PGR mefluidide was discontinued several years ago, it spurred turf researchers and superintendents to investigate other ways to deal with seedheads. Mechanical seedhead removal with vertical mowing, brushing or grooming is an approach that has gained some traction. Just take care to avoid injuring the turf since it hasn’t fully awakened from its winter slumber and will be slow to recover.
For more information on seedhead suppression or any other issues on your course, reach out to your regional USGA agronomist.
References
Mitich, L. W. (1998). Annual bluegrass (Poa annua L.). Weed Technology, 12(2), 414-416.
Askew, S. D. (2017). Plant growth regulators applied in winter improve annual bluegrass (Poa annua) seedhead suppression on golf greens. Weed Technology, 31(5), 701–713.
Northeast Region Agronomists
Darin Bevard, senior director, Championship Agronomy – dbevard@usga.org
Elliott L. Dowling, regional director, East Region – edowling@usga.org
Brian Gietka, agronomist, Northeast Region – bgietka@usga.org
Information on the USGA’s Course Consulting Service
Contact the Green Section Staff