California red scale updates: This season is early!

California red scale updates: This season is early! 

California Red Scale development is running well ahead of schedule, monitor now for fourth generation flights and prepare for additional generations. As of July 26, 2026 CRS development across the San Joaquin Valley continues to progress significantly ahead of what has been observed during most recent seasons, and about 4-6 week ahead compared to 30 year average. Degree-day accumulations indicate that the fourth generation is approaching rapidly, with the potential for a complete fifth generation in many citrus-growing regions if warm fall temperatures persist.

As of July 26, 2026, accumulated degree-days (base 53°F) from the county-specific biofix are: 

Historically, fourth-generation activity begins late in August or early September. However, based on the current season's accelerated heat accumulation, these events are expected to occur substantially earlier than normal.

What Should Growers and PCAs Do Now?

1. Monitor orchards immediately for the fourth male flight.

Deploy or replace pheromone traps now to detect the onset of the fourth male flight. Monitoring this flight is especially important because it provides valuable information about how advanced the season has become and helps anticipate late-season crawler activity that can threaten fruit quality and influence management decisions for the remainder of the year.

2. Evaluate live California red scale populations and take action if needed.

If live CRS populations are present on fruit or wood, there are still two major crawler emergence periods remaining this season. Existing infestations are likely to continue increasing unless managed. Depending on orchard conditions and your integrated pest management program, consider timely insecticide applications targeting crawler emergence or augmentative releases of Aphytis melinus where appropriate.

3. Continue monitoring clean orchards.

Even if fruit appears clean, continue monitoring both fruit and woody tissue. California red scale frequently survives on twigs and interior wood where coverage can be less effective and infestations may go unnoticed until populations build. Detecting these populations early will improve management decisions before late-season crawler emergence.

Seasonal Phenology Update

California red scale development is closely tied to heat accumulation, allowing degree-day models to accurately predict key biological events throughout the season. These predictions remain one of the most valuable tools for timing monitoring and management activities.

Major seasonal events, crawler emergence and male flight occur at approximately at 550 DD. For example, after biofix, first generation male flight occurs at 550 DD, and second generation flight occurs 550 DD after crawler emergence. Historically, average weather would place major events like 4^th generation flight for late August or early September and fifth generation crawler emergence rarely occurring. However, this season the projections are considerably earlier.

Compared with historical averages, the entire seasonal phenology is advancing by approximately two to three weeks in many production areas.

EXTERNAL IMAGE

Figure. Figure showing historical occurrences comparing it with 2026 projections. Note, historically not enough heat units for fifth generation crawler, except in Tulare County in November. 2026, all three counties are predicted to have fifth generation crawlers. 

Why this matters for CRS management?

California red scale populations can increase rapidly during the latter half of the season. When infestations become established during mid-summer, each subsequent crawler generation has the potential to further increase fruit infestation prior to harvest.

The current season is progressing much faster than growers have experienced in recent years. If temperatures during October and November remain above the lower developmental threshold (53°F), much of Tulare and Kern Counties, and potentially Fresno County could experience a biologically complete fifth generation. This would extend crawler activity well into the fall and increase the risk of late-season fruit infestation.

Because two additional crawler emergence periods remain, orchards with active populations today are likely to experience increasing pressure unless management actions are taken.

Conversely, orchards that currently have little or no fruit infestation should not become complacent. Monitoring should continue because populations often persist on interior wood and scaffold branches where they are less visible and more difficult to control. Detecting these populations before crawler emergence allows growers to make more effective management decisions and protect fruit through harvest.

Using Degree-Day Models to Improve Timing

Monitoring trap captures together with degree-day accumulations remains the foundation of an effective California red scale management program. Pheromone trap catches identify the onset of male flights, while the degree-day model predicts crawler emergence, allowing treatments to be timed when the susceptible crawler stage is present.

For county-specific degree-day accumulations and predicted biological events, visit: Lindcove Research and Extension Center California Red Scale Degree-Day Updates
For monitoring guidelines, treatment thresholds, and current management recommendations, consult the: UC IPM California Red Scale Pest Management Guidelines

Take-Home Message

The 2026 California red scale season is developing substantially earlier than normal across the San Joaquin Valley. Fourth-generation activity is approaching rapidly, and many orchards may experience a complete fifth generation this fall if warm temperatures persist. Timely monitoring over the next several weeks will be critical for protecting fruit quality, making informed treatment decisions, and preparing for an extended California red scale season.