By Andrew Hollman
At the Turfgrass Research, Outreach and Education Center (TROE) we plant numerous trials by national organizations to help evaluate newer cultivars of species commonly used in Minnesota. In our ratings of these plots we often see cultivars that stand out in their response to a disease, tolerance to moisture stress, or maintenance of quality with lower inputs. At extension events and field days we often talk about these trials and show off these well-performing cultivars or species and encourage their use. The ability of a turfgrass manager to incorporate different species or new cultivars may present different challenges depending on the site and use of the area. Some turfgrass managers might have the time and resources to re-grass an area and keep it out of use until it is established. For others, the site might be used well into the fall and is too critical to take out of use. Golf courses are a good example of sites where users will continue playing until the weather no longer allows it. Also, golf course putting greens are an area that takes a considerable amount of resources to re-grass and affects the overall usability and profitability of the course.
With our previous studies we have seen that we can kill perennial ryegrass turf when herbicide is applied in late October and even in November at the time of dormant seeding, and that dead vegetation serves as a mulch through which the new seed can grow and establish. This led us to wonder whether we could use this same approach on a creeping bentgrass green. Transitioning a putting green to a newer creeping bentgrass cultivar without stripping out the old turf would be a great management tool for golf course superintendents.
In the fall of 2024 we laid out a trial area on our ‘L-93’ creeping bentgrass green that was established in 2003 on a USGA specified rootzone (Figure 1). Since creeping bentgrass is stoloniferous, we were concerned that a single application of herbicide would not be sufficient to kill it. For this reason we imposed four different treatments to assess herbicide timing and whether multiple applications were needed: 1) untreated control (no herbicide), 2) late October herbicide application, 3) dormant seeding herbicide application (usually middle of November) and 4) late October and middle November herbicide application. The entire plot was seeded following the November herbicide application. Seeding was done with a drop spreader using bentgrass seed mixed into an organic fertilizer to aid in its dispersal. After seeding half of each plot was heavily topdressed with sand. By the time we seeded the plot on November 19, 2024 (Figure 2), we could clearly see the herbicide effects on the plots that had received a late October application.
Whether the herbicide application in November would be effective is hard to assess visually until growth resumes in the spring. In January when we did not have snow (Figure 3), it did not appear that we could pick out the untreated plots from the dormant seeding herbicide application. By the end of February (Figure 4), it was still difficult to see whether the dormant seeding herbicide application had an effect. With some warmer temperature in March we started to see differences in green-up corresponding only to the untreated plots (Figure 5). As we continue through the spring we will see how effective our herbicide applications were and whether the dormant seeding can successfully re-grass this area and maintained.
