May is the time of year when annual bluegrass (ABG) is in full on seedhead production mode here in West Lafayette. The seedheads are unsightly and may disrupt playability in some instances. More importantly, compared to other fairway grass species as ABG populations increase the seasonal reliability of the surface becomes compromised and fungicide requirements for summer survival increase. Remember the old adage “one years seeding equals seven years weeding!” Thus, golf course managers are often asking what they can do to reduce seedheads and ultimately ABG populations. One starting point may be a fairway grass renovation to superior more contemporary bentgrasses. Improved species selection coupled with a chemical suppression program like regular use of root-absorbed PGRs and/or selective annual bluegrass herbicides. In September of 2020 we planted 24 bentgrasses as part of the National Turfgrass Evaluation Program to evaluate their seasonal performance over five growing seasons. In addition, to general cultivar evaluation, the bentgrass cultivar plots were “split” and one side has been receiving a seasonal ABG suppression program. To date there have been both differences in encroachment by cultivar as well as the ABG suppression program (see image). For the cultivars the ABG percentages ranged from 10-70% (mean = 25%) and for cultivars subject to a PGR/herbicide program percentages ranged from 0.5-18% (mean = 3%). In general, newer denser bentgrasses had substantially less ABG than older cultivars. The benefits of a root-absorbed PGR for seasonal ABG suppression is also noted. This study will be evaluated for two more growing seasons and stay tuned for 5-year summary at a future Indiana Green Expo or come see us and the turf plots at our July Field Day.

Overview of bentgrass cultivar trial May 2024, demonstrating the level of annual bluegrass encroachment in our NTEP bentgrass fairway trial. Notice some areas are mostly “clean” while others have substantial annual bluegrass populations in year 4 or this 5 year study.