GDD model for PGR's

We use plant growth regulators (PGR’s) regularly on most of the playing surfaces on the course. We also use them on the driving range and both soccer fields. PGR’s play an important role in maintaining the turf all around Bretton Woods and this year we have fine-tuned the timing for application. We are now using a Growing Degree Day (GDD) model for all of our PGR applications.

PGR’s do exactly as their name implies, they regulate the growth of the plant. They do not stop growth (unless applied at very high rates), but limit the amount of growth that occurs. By limiting the growth, grass can become healthier because the plant’s resources can be used for other things. This is certainly a positive aspect for the Grounds department. Also, there can be surges in growth as a grass plant comes out of growth regulation, which is not healthy for the plant. So, by maintaining a relatively consistent amount of the PGR in the plant, the grass does not go through big swings of growth and stays generally healthier. The PGR effect extends to the maintenance side of our work as well.

PGR’s allow for less mowing. Less mowing means less labor, less fuel, and more time for other jobs. We can reduce the amount of times we have to mow greens or tees or fairways from every day to every other day or every third day depending on other circumstances. This leads to monetary savings and man-hours to be used elsewhere. All while not diminishing the product presented to members and guests.

There are many different varieties of PGR’s and several different modes of action. Without getting too technical, the bottom line is they all work to alter the natural growing habits of the plant. However, trying to time when you apply the PGR used to be very subjective. We would monitor how much grass clippings were in our bucket after we finished mowing, or visually inspect the fairways to see how long the turf was compared to when our last cut happened. Each of these methods can be useful and still provide information. However, in the last few years, more and more research has been conducted showing that by using GDD models, we can accurately monitor the amount of regulation the grass is under and time our next application based on the breakdown of the chemical inside the plant.

GDD models have been used for years and years to time all sorts of things in all agriculture. We have been using a GDD model for seed heads on the greens for several years. But, with this new research we have extended their use to include our PGR application timing. One of the lead researchers has even developed a spreadsheet and an app, both of which can be downloaded and adjusted to individual course needs to help monitor GDD. The research has determined at what point the amount of PGR still in the plant is too low to provide adequate growth regulation. This has been converted to a simple number of growing degree days. For example, for the PGR we use on greens, we need to re-apply every 200 GDD.

We are using the spreadsheet to monitor the fate of our PGR applications on the greens, all of the Bermuda grass, the driving range, and both soccer fields. We simply plug in the mean temperature of each day and the spreadsheet calculates the approximate percentage of chemical still in the plant. Once we reach 200 GDD, the percentage of chemical in the plant is below our needs and we re-apply. This number is different for different chemicals but the idea is the same.

Now, we can apply our PGR’s with more objective data. Keeping an eye on the weather, which we do anyway, no enables us to be more efficient and effective with our PGR applications as well.

Etiquette Reminder of the Month

In addition to repairing your own ball mark on every green, please repair at least one other as well.

See you on the course!

Joe

jvillegas@bwrc.org