KAC Citrus Entomology
University of California
KAC Citrus Entomology

California Red Scale Degree Days

Biofix: 1st male flight  (early March)
Lower developmental threshold:

Stage of Development

Degree-days from male flight biofix

Crawler emergence


Third instar virgin females


Beginning of next male flight


Current CRS Degree-Day Accumulations

DD as of 1 December 2019

Madera County: 4083

Biofix: 29 Mar


Fresno County: 4414

Biofix: 22 Mar 


Tulare County: 4534

Biofix: 22 Mar


Kern County: 4653

Biofix: 15 Mar

Cimis #125


Degree-Days to Complete a Generation: Approximately 550 degree-days after the males fly (the biofix) and mate with the females, the first generation of crawlers (1st instar scale) will begin to emerge. The crawler stage is most susceptible to pesticides and 1 to 3 weeks after they first begin to emerge is the optimal time to apply most pesticides. As the season progresses, the scales continue to molt and develop into 2nd instars, then at approximately 800 degree-days the females become virgin 3rd instars. This point in time is optimal for releasing Aphytis wasps because this is the growth stage that they prefer to parasitize.

Approximately 1100 degree-days after the first generation of males begin to fly, the 2nd generation of males begin fly. Each of the next three crawler generations will emerge 550 degree days after the preceding male flight. Thirty-year temperature data can be used to approximate when these events are likely to occur. Current temperature readings can then be used to adjust the model. Weekly pheromone trap counts and crawler tapes can be used to confirm that these events are happening as predicted.

Generations per year: 4 to 5 generations per year.

Webmaster Email: eegraftoncardwell@ucanr.edu