The warm temperatures we have experienced this week remind us spring will be here shortly. Although the turf has not come out of dormancy, I'm already thinking about Poa annua seedhead suppression. Seedheads will not appear until May, but multiple growth regulator applications will be made before then to ensure the putting surfaces are pristine.
One way turf managers try to predict seedhead emergence is by monitoring growing degrees (GDD). GDD models have been developed to determine the best time to apply growth regulators to control the prolific seedheads that Poa annua produces each spring.
What are growing degree days (GDD)?
The sum of the number of degrees by which each days average temperature exceeds a base temperature (32°F).
How are GDD calculated?
GDD = [(maximum temperature + minimum temperature) /2] - (32)
For example on March 10, the high of 59°F and the low of 52°F resulted in 24 GDD.
GDD = [(59+52) /2] - 32
GDD = 24
GDD = 24
I keep track of the GDD accumulation and will start making seedhead suppression applications when we reach 200 GDD. Applications continue throughout the spring. Below is a spreadsheet of March GDD accumulation so far.
