We chatted recently with Dr. Cale Bigelow, assistant professor of agronomy and turfgrass science at Purdue University, about the latest research, developments, and use of plant growth regulators on golf courses.
What has the latest research on PGRs shown in dealing with Poa growth shown?
The latest research has validated a lot of what we already knew: Certain products like flurprimidol and paclobutrazol work. What we are trying to figure out are the details. For example, are there things you can do to enhance effectiveness of the products. Annual bluegrass is such a genetically diverse plant, so the concept that there is a “one-size fits all” solution is unlikely to completely work. Some of the seedhead suppression work we did this spring was surprising. Most years we can get 80 percent suppression with some tried and true products, assuming that the “proper” application timing is targeted and hit. This spring was much less, even though we hit the right growing degree-day timings. Sometimes it just is what it is, and that is what keeps us asking questions.
When are the best times for superintendents to apply PGRs to control Poa?
For annual bluegrass suppression, based on nearly 20 years of personal observation, I have resigned myself to the fact that complete, 100 percent “control” is likely unachievable. However, in bentgrass areas, the critical period is basically September through October in most cool-humid regions. This may help suppress emerging seedlings and also perhaps affect winter hardiness of the weaker existing plants.
What are some of the biggest mistakes superintendents make when using PGRs?
Giving up too quickly! You have to be invested in a long-term program. A single or short period of low application rates will likely not be effective. Be holistic in your thinking, everything from growing environment (shade and excess soil wetness favor annual bluegrass), to fertility source and mowing height. If it is just general “regulation” of an area (fairways, tees, etc.), a product like trinexapac-ethly is metabolized under warm, humid conditions. This may result in rapid rebound, excess clippings and perhaps scalping.
How much of a difference can PGRs make on the course, especially on the greens?
They are a game-changer. In recent years, some colleagues have been exploring the economics and potential plant health benefits of alternating mowing and rolling programs. Green surface smoothness and trueness of ball roll is a legitimate concern for golfers of any ability. With PGRs in the program, “if” a manager wants to insert an extra roll instead of a mow (normally less expensive), the surfaces will remain smooth with reasonable ball speeds. Where I have seen the biggest benefit of PGRs has been during wet periods.
