The term 'Growing Degree Days (GDD)' is becoming increasingly common in golf course management. While it might still seem unfamiliar, it's highly likely to become an essential metric that course management teams must adopt in the future. The reason is quite simple.
Because grass doesn't grow according to a calendar.
Even if the same three weeks pass, three weeks in spring are completely different from three weeks in midsummer. During cooler periods, turf growth progresses slowly, while during warmer periods, it accelerates significantly. If you simply calculate work timing by date, such as "3 weeks after the last application," the actual turf growth response and management timing can become misaligned.
The Korea Golf Course Management Association emphasizes course management utilizing Growing Degree Days.This also aligns with the current trend. The core concept isn't difficult. Now, course management shouldn't solely rely on past experiences like 'this time last year,' but rather, also verify with data the actual growth conditions the turf has experienced.is essential.
Growing Degree Days (GDD) are the cumulative sum of temperatures conducive to turf growth, accumulated day by day. Simply put, it's a quantitative metric that shows how much growth-promoting conditions the turf has actually experienced.
Understanding this difference completely transforms how you approach course management timing. The paradigm shifts from asking "How many days have passed since the last task?" to "How much growth-promoting conditions has the turf experienced during that period?"
Growing Degree Days (GDD) are particularly useful when determining the reapplication timing for PGR (Plant Growth Regulator).
PGRs are used to regulate turf growth, reduce clippings, and maintain consistent green speed and course quality. However, The duration of the effect varies each time depending on the weather. Even if a 3-week interval was appropriate in spring, in summer when temperatures soar, the growth of clippings can increase sharply even before 3 weeks have passed. This is because the growth rate of turfgrass varies depending on temperature conditions, even when applying the same product in the same amount.
Therefore, it's time to shift our operational standards.
If accumulated temperature is building up quickly, you can anticipate and prepare for the PGR effect wearing off sooner than expected. Conversely, if accumulated temperature accumulation is slow, there's no need to rush operations simply because a certain number of days have passed, thereby reducing unnecessary resource waste.
Of course, you cannot determine all course management tasks based solely on accumulated temperature data. The actual turfgrass response can vary depending on on-site soil moisture, drainage conditions, shade, ventilation, fertilization history, and disease occurrence history.
Therefore, it's best to understand accumulated temperature not as an absolute answer, but as a 'signal indicating when to physically inspect the site'. When the accumulated temperature signal is triggered, you must cross-verify whether clippings have increased on-site, if there are changes in turf color and density, or if green speed has changed, to maintain a perfect course.
What's important for future golf course management isn't just "doing well by feel." Explain with data why those pest control and operational decisions were made at that time.You need management that can do this.
Accumulated temperature is the most objective criterion to support such decisions. It serves as a shared indicator for both headquarters and the field, and provides a clear common language for course management team members to coordinate operational timing.
Meisa Green currently offers a tool for greenkeepers to easily determine the optimal timing for PGR reapplication, the 'Accumulated Temperature Calculator'. We are preparing a new feature. Before the calculator launches, we are first distributing the [Key Guide to Growing Degree Day Utilization], which explains how to understand and immediately apply Growing Degree Days in the field.
For PGR reapplication timing, manage it precisely with Growing Degree Days instead of dates. You can instantly download the practical guide from the link below.