Extension Advisory for Citrus Growers on California Red Scale as of April 24, 2026
California red scale is a key pest of citrus in the SJV. Its life cycle starts as crawlers produced by overwintering females from the past season. Crawlers move and find a suitable place to start feeding. Once they have settled, they do not move. Current degree-day accumulation since the March 1 biofix (base 53°F) indicates that California red scale (CRS) is actively progressing through a critical early-season phase across the southern San Joaquin Valley. As of April 24, conditions are as follows:
- Kern County: 721 DD
- Tulare County: 738 DD
- Fresno County: 639 DD
The biological threshold for first-generation crawler emergence is approximately 550 DD, meaning all three counties are now firmly within the active crawler emergence window.
What is happening in the field?
Across Kern, Tulare, and Fresno counties, CRS populations have reached or exceeded the point where first-generation crawlers are emerging and dispersing. This stage represents the most vulnerable period in the insect’s life cycle, as crawlers move from under the protective scale cover to new feeding sites on fruit, leaves, and wood.
EXTERNAL IMAGE
- Kern and Tulare (720+ DD): Crawlers are actively emerging and dispersing, with populations likely slightly more advanced and sustained due to higher heat accumulation.
- Fresno (~639 DD): Early crawler emergence is underway and expected to increase steadily over the coming days to weeks.
This period represents the primary management window for targeting CRS immatures.
Scouting: First and most important step
Growers and PCAs should prioritize field-specific monitoring, as degree-day models indicate timing but not pest pressure.
Key scouting actions:
- Look for white cap stage on fruit and twigs (indicator of crawler emergence)
- Pay attention to hotspots, especially:
- Orchard borders
- Dusty blocks
- Areas with ant activity, which can protect scale colonies
As field conditions vary significantly within and between orchards, management decisions should always be based on confirmed crawler presence and population levels, not degree days alone.
Management implications: targeting crawlers
This is the optimal window for control actions, if treatment is needed. Once crawlers settle and develop wax coverings, they become significantly harder to manage.
When populations justify treatment:
- Time applications to peak crawler emergence (NOW!!)
- Target immature stages (crawlers/early settlers) for best efficacy (IGRs only work when immatures are present, other pesticides also work best on immatures)
- Ensure good coverage, especially in dense canopy and interior wood
Where possible, growers are encouraged to:
- Use softer chemistries that are compatible with beneficial insects
- Preserve natural enemy populations (parasitoids and predators) that contribute to long-term suppression
- Release Aphytis melinus to augment biocontrol
- Integrate treatments within a resistance management program
Mating disruption reminder
For orchards using mating disruption as part of their CRS IPM program:
- Mating disruption dispensers are likely already in place prior to first flight (March 1)
- If not yet in place, they should be applied before the second male flight (~1100 DD; expected late May)
- Timely deployment is critical to prevent successful mating in the upcoming generation
What to watch in coming weeks?
- Second male flight: ~1100 DD (late May)
- Second-generation crawlers: ~1650 DD (early–mid summer)
Current actions directly influence the size of the next generation. Early suppression now reduces later-season pressure.
Stay Updated
My team updates Degree days for three counties Kern, Tulare, and Fresno and posts information on Degree Days. Growers are strongly encouraged to follow ongoing degree-day and pest development updates. More citrus pest-related information on Citrus IPM. Also subscribe to Citrus IPM News for updates related to citrus pests, extension and outreach activities via UC.