Small Broomrape is a common weed species that can destroy red clover populations if not controlled. The Small Broomrape growing degree day model, uses heat units and time as a method to estimate plant phenological stages through the growing season. This can be helpful to time herbicide applications before stalk emergence.

Calculating Growing Degree Days

For this model, a lower temperature threshold of 32F is used to calculate growing degree day accumulation. A biofix date (for beginning gdd accumulation) of January 1 is recommended for the Northern Hemisphere. 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. The window for herbicide application will occur between 1440 and 1800 GDD (F), flower stalks will emerge at 1980 GDD (F).

Learn More:

Hanan Eizenberg, et al. “A Predictive Degree-Days Model for Small Broomrape (Orobanche Minor) Parasitism in Red Clover in Oregon.” Weed Science, vol. 53, no. 1, 2005, pp. 37–40. JSTOR. Accessed 20 Mar. 2023.