California Red Scale Degree Days
The 2026 California red scale season has begun. Many PCAs report that they started catching male flight on pheromone trap cards between March 1–3 across Kern, Tulare, and Fresno Counties. We caught fliers in trap at Lindcove REC on March 2. As of now, male captures have not yet been reported from Madera County. These early male flights mark the beginning of the first generation and signal that growers and PCAs should begin closely monitoring orchards for crawler activity in the coming weeks. You can monitor degree days by using UCIPM Weather Model for California red scale. Click the link, and choose the nearest station. Enter biofix date, March 1 for Kern, Tulare, and Fresno Counties. The weather model will calculate the accumulated degree days for you. For stations that have more than 10 years of historical data, it will also calculate average DD accumulation for the future dates. However, not all CIMIS stations have ~10 years of data. For example, out of the three CIMIS stations in Tulare County, i.e., Delano, Lemon Cove, and Lindcove, only Delano has ~10 years of data.
What is CRS Biofix?
CRS Biofix is the start of California red scale activity for this season. As weather warms up and heat units are accumulated above the lower developmental threshold of this insects, overwintering females start producing crawlers which develop. Males’ complete development and fly to find third instar females to mate.
How to interpret CRS DD and incorporate it into CRS IPM: It takes 550 Degree Days (heat units above the lower developmental threshold of California red scale) from Biofix day (March 1 for 2026) to first generation crawler emergence. UCIPM recommends treatments be applied when the population consists mainly of immatures, as immatures are the most susceptible to treatments. Second generation flight will occur at 1100 DD after the Biofix, and second-generation crawler emergence begins at 1650 DD. By using the CRS Degree day model, we are able to predict the seasonal phenology of CRS, thereby making targeted applications. My team will be monitoring degree days and updating them on the LREC website. Stay tuned!
What do males on the trap cards mean for management?
Pest control advisors have long used pheromone cards to monitor males and degree days to predict successive life event (crawler emergence) for timely management of CRS. Trap numbers may be different depending on the management choice.
- IGRs and mating disruption – few male scales on the card as these options affect males more than it does females. You may have lower males on card but have high CRS populations.
- Aphytis and Movento – Aphytis targets third instar females, thus affecting females more than it does to males. Also, Movento controls CRS on twigs but not on wood. If Aphytis or Movento or both are used, you may see higher males. If Movento was used, check the inner canopy branches, top of the tree for CRS patches.
Check https://lrec.ucanr.edu/Citrus_IPM/Degree_Days/. for biweekly updates of CRS degree days.
For Management is targeted at 1st and 2nd generations as the crawlers are emerging. Based on previous years, first generation crawler emergence occurs around 2nd/3rd week of May. As the degree day accumulation is temperature dependent, monitoring is critical to predict accurately. Visit Pest Management Guidelines for CRS for more information.