California Red Scale Advisory Issued

Sandipa Gautam, University of California area citrus integrated pest management (IPM) advisor, issued an Extension advisory for California red scale (CRS). The scale is a key pest of citrus in the San Joaquin Valley. Key points of the advisory are as follows:

CRAWLERS ARE ACTIVE

The CRS 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 March 1 indicates that CRS is actively progressing through a critical early-season phase across the southern San Joaquin Valley.

As of April 24, Kern, Tulare and Fresno counties were firmly within the active crawler emergence window. Across those 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.

In Kern and Tulare counties, crawlers are actively emerging and dispersing, with populations likely slightly more advanced and sustained due to higher heat accumulation.

In Fresno County, 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.

PRIORITIZE SCOUTING

Growers and pest control advisers should prioritize field-specific monitoring, as degree-day models indicate timing but not pest pressure.

Look for the white cap stage on fruit and twigs (indicator of crawler emergence). Pay attention to hotspots, especially orchard borders, dusty blocks and areas with ant activity, which can protect scale colonies.

TREATMENT TIPS

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.

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 (Insect growth regulators only work when immatures are present; other pesticides also work best on immatures).
• Ensure good coverage, especially in dense canopies and interior wood.

Where possible:

• 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. 

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 (expected in late May).
• Timely deployment is critical to prevent successful mating in the upcoming generation. 

Current actions directly influence the size of the next generation. Early suppression now reduces later-season pressure.

See Gautam’s full advisory here.

Source: University of California Agriculture and Natural Resources