As we head into late August, we’re seeing an accelerated development of California Red Scale (CRS) across California caused by the higher temperatures this year. This is raising concerns about an earlier 4th generation and the possibility of a 5th generation.
Below, we’re sharing an update on CRS development across the state, how 2026 compares with previous years, and some strategies to help you better prepare for the later CRS generations.
Using data from the Semios weather station network, we've created the following map showing average CRS degree-day accumulation across California. The data is based on a March 15 biofix and shows degree-day accumulation as of August 6, 2026.
The chart below breaks out CRS degree-day accumulation by county in California:
Using Semios’ historical weather data collected across California, we also took a look at how this year’s degree-day accumulation compares against previous seasons.
From the March 15 biofix through August 6, the average CRS degree-day accumulation this year was 8.2% above the 2023–2025 average and the highest of the four years analyzed.
You can see how the average degree-day accumulations in 2023-2026 compare in the chart below:
The consistently warmer temperatures have been accelerating CRS life cycles, making the 4th generation arrive earlier and a 5th CRS generation more of a possibility. It's critical to keep the 5th generation under control to start off next season with lower overwintering pest numbers.
As temperatures keep climbing each year, it’ll become the norm for growers to apply more insecticides to keep CRS populations under control. Rather than relying solely on the insecticide chemistries available, growers can implement different IPM tools such as mating disruption to reduce the risk of building insecticide resistance for better long-term results.
Protecting your crop with mating disruption
Growers using passive mating disruption products may need to consider whether replacements are needed. Passive mating disruption products release 24 hours a day and the release rate is impacted by temperature. This means the hotter the season, the greater the risk of having insufficient pheromone coverage later in the season.
On the other hand, aerosol emitters like the ones used in Semios variable rate mating disruption products work differently as their release rates aren’t impacted by warmer temperatures. Instead, Semios’ aerosol emitters are metered with an optimized dispensing duration to target only when pests are active. This allows us to extend coverage late into the season, and growers are still covered even during hotter years.
Having an effective mating disruption program in place is valuable as it’ll help reduce the overwintering population of CRS for next year when accompanied with good IPM practices.
Leveraging on-site data to better time sprays
The trend of increasing temperatures is leading to even greater variability in pest and crop development across the state, which you can see in the regional reports above. It’s important to invest in on-site weather data to get the information you need to make more accurate pest management decisions.
On the Semios app, users can view their current site-specific CRS degree-day accumulation and a 14-day forecast. This helps them better time sprays to get the best coverage, targeting when the pest is most vulnerable and is easier to suppress.
Other helpful tools on the Semios app include:
Monitoring and scouting tips
It’s important to maintain regular scouting trips and leverage traps to keep on top of what’s happening in your blocks and avoid having undetected pockets of CRS grow into a bigger problem.
As a general guideline, visually checking roughly 20-30 fruits per trees, on 20-25 trees per block, helps you get a good representative sample of the pest life stage in your orchard.