What are GDD? In simple terms, GDD is a measure of heat accumulation. GDD can be used to track weed and insect activity, as well as more pleasant things such as when flowers will be blooming.
Whether it's a pre-emergent herbicide for Crabgrass, or a product for weevil control, these applications can't be timed for optimum efficacy if simply based on a fixed, predetermined date. More often than not, doing so will mean you made the application either too early or too late, and the results will reflect this.
This time of year, one of the most important green spray applications is for the prevention of Poa seedhead development on the putting surfaces.
|Limiting Poa seed development is critical in maintaining a smooth putting surface.|
In the case of spraying to prevent Poa seedhead development, we start tracking GDD in January, and use 32 degrees as a base. Each day, the high and low temperatures are averaged and 32 is subtracted from this. (Negative results are not included, based on the assumption that a plant's development basically remains static on those days.)
As you can see below, due to the record warmth this year, we accumulated over 500 GDD through February. How does this compare to other years?
|2017 Growing Degree Days|
Well, through February, 2015, we had only accumulated 68 GDD. In other words, we are way ahead of 2015, and spraying on the same date these two years would yield entirely different results. The initial spray for Poa seed prevention went out this year during the last week of February, whereas it was not made until the first week of April in 2015.
|2015 Growing Degree Days|
So, how have we done in the past with our seedhead control when using GDD? The untreated check plot in this photo had significantly more seeds develop than the rest of the green. While we'll never achieve 100% control, our goal is to avoid having the greens feel like you're putting on cauliflower in the spring.
|Untreated check plot.|