Bluegrass (Poa annua) is a common weed species in a varieties of regions. The Bluegrass growing degree day model developed by researchers, uses heat units and time as a method to estimate plant phenological stages through the growing season. This can be helpful to predict plant emergence and to time herbicide applications before seed production occurs.

Calculating Growing Degree Days

For this model, a lower temperature threshold of 13C is used to calculate growing degree day accumulation. For the Northern Hemisphere, April 1st, should be used as a biofix, the date when to start growing degree day accumulation. Growing degree days can be calculated from daily high and low temperatures, or via the Pest Prophet app, which uses hourly temperature data for a given field. Peak seed production will occur between 364 GDD (C) and 433 GDD (C).

Learn More:

Danneberger, T. K., and J. M. Vargas, Jr. 1984. Annual Bluegrass Seedhead Emergence as Predicted by Degree-day Accumulation. Agronomy Journal 76:756-758.tshade (Solanum nigrum and S. ptycanthum) growth using degree-days. Weed Science 40: 86-89.