Plant growth regulators seemingly failed at suppressing annual bluegrass seedheads on putting greens this year.
We have been evaluating different products and different application timings for seedhead suppression for about 20 years at the Michigan State University Hancock Turfgrass Research Center. Embark is no longer being produced, so those who haven’t stockpiled it over the years can no longer use what has always been considered to be the most effective product for seedhead suppression.
Over the years, we have developed growing degree-day (GDD) models to better time applications of Embark, and Proxy plus Primo Maxx. After years of research and talking with other researchers and golf course superintendents, many applications still fail to effectively suppress seedhead production in annual bluegrass greens and fairways. Efforts to suppress seedheads in East Lansing, Michigan, failed in 2018 and many golf course superintendents also appeared to have struggled with seedhead control.
We applied different combinations of plant growth regulators in 2018 using the Proxy/Primo GDD timer within the application window of 200 and 500 GDDs base 32 F, available at GDD Tracker. This year in East Lansing, the application window was from March 30 to May 1, 2018. First applications were made April 25 and although there was some seedhead suppression, we consider it a failure as more than 10 percent of the surface area was covered with seedheads. We waited for the end of the application window because we had yet to mow until a few days before April 25 because it was so cold.
Many in Michigan experienced the same process by waiting for growth before making the first application. In 2017, the application window using the same GDD model ended April 10.
So, what went wrong this year? What good is a window of application if it can still fail?
It’s important to remember that seedhead production in annual bluegrass can be affected by many factors. We use a GDD model to time our applications that only accounts for the accumulation of heat units. There may be other climatic factors that affect the timing of peak seedhead flush that we aren’t measuring. Furthermore, annual bluegrass is so biologically diverse that seedhead production can vary greatly.
It’s difficult to know exactly why many seedhead suppression efforts failed this year. However, here are a few thoughts.
There is evidence to suggest that a PGR application must be timed before a seedhead emerges from the plant. The model is designed to signal application timing before emergence. Seedheads may emerge and not be easily viewed without some hands-on investigation of plants, so investigate. Look closely for emergence in south-facing slopes or other areas that may heat up faster than others. You could use these observations to help fine-tune your application even within the window given by GDD models. In the end, apply early rather than late. Once seedhead emergence begins, it is too late.
If you are applying Proxy plus Primo, start your applications in late fall. Proxy plus Primo fall applications followed by GDD-timed Proxy plus Primo applications in spring have proven to consistently provide better seedhead suppression than spring only applications. We have made our fall-timed applications in the end of October to the beginning of November and had good results. If you are spending the time and money in spring to control seedheads, add a fall-timed application for a little insurance.
Whether your seedhead suppression failed or not in 2018, keep trying. As a researcher, we observe the “failed” treatments next to the untreated plots, although the objective is 100 percent seedhead control, any amount of control makes a big difference when compared to the untreated plots.