Japanese Knotweed Psyllid (Aphalara itadori), is an important insect used for biological control of weeds in the knotweed family. Researchers have developed a growing degree day model for Japanese Knotweed Psyllid that can help predict emergence and egg-laying of overwintered adults and timing of the following generations.

Calculating Growing Degree Days

The Japanese Knotweed Psyllid model uses a lower threshold of 43F and an upper threshold of 95F. It can be calculated with daily high and low temperatures, using the sine model to estimate growing degree day units, or the Pest Prophet app can be used to calculate GDD accumulation from hourly temperature data for a specific field.

For this model, the “biofix” date, or date from which to start accumulating growing degree days, should be set to Jan. 1st for the Northern Hemisphere.

Spring emergence begins at approximately 420 GDD(F) and with egg-laying beginning at 521 GDD (F). Egg-laying/ adult stage of the next generation occurs at approximately 2167 GDD (F) after the biofix date. The model can then be used to predict adult emergence for the next 3-4 generations in a season.

Sources:

Myint, Y.Y., K. Nakahira, M. Takagi, N. Furuya, R.H. Shaw. 2012. Using life-history parameters and a degree-day model to predict climate suitability in