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How to identify it
- Young scales on the leaves are flat and almost translucent, and they grow slowly through summer and fall.[1]
- By November the second-stage scales turn a mottled dark brown and start moving from the leaves to the twigs, where they turn gray.[1]
- On leaves they appear only in summer and fall, and the nymphs are all about the same size.[1]
- Crawlers settle mainly on the undersides of leaves; in severe infestations they also settle on upper leaf surfaces and twigs, and rarely on fruit.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Brown soft scale | A similar soft scale found in the same areas, but it has several generations a year, so colonies mix every stage and all stages are present on leaves and twigs year-round.[1] |
Where it lives
A citrus pest in California. UC IPM says it is a problem only in the San Joaquin Valley; in Southern California parasites keep it so scarce it is almost never seen.[1]
Biology and life cycle
Crawlers appear from May through August and settle on the leaves. The scales molt only once during summer and fall.[1]
Their move from leaves to twigs peaks in February and March. On the twigs they develop faster, and by late April they molt into adult females.[1]
Each female lays 1,000 to 1,500 eggs from early May to early August. The eggs hatch in two to three days and the crawlers move out to the leaves.[1]
There is only one generation a year, and there are no males.[1]
Damage and signs
- A severe infestation reduces tree vigor, kills twigs, and reduces flowering and fruit set.[1]
- The scales excrete honeydew onto leaves and fruit. Sooty mold growing on it interferes with photosynthesis and gets fruit downgraded at packing.[1]
- In field experiments on Valencia oranges, adult scales cut average tree yield by up to 43% and raised sooty mold prevalence by at least 45%, with significant effects at densities below 0.1 adults per branch or 1 nymph per leaf.[2]
Health risk
The sources describe it only as a citrus pest; neither mentions any risk to people or pets.[1][2]
Control
Prevention
Check twigs closely in April and leaf undersides in late July, and make sure you are not looking at brown soft scale. UC IPM's leaf sample calls for a spray when any one of four sampled rows has five or more of 25 leaves with live scale; researchers have suggested lowering the twig threshold because damage occurs at lower densities.[1][2]
Biological control
Parasitic wasps, Metaphycus luteolus, M. stanleyi, M. nietneri, M. helvolus and Coccophagus species, control it in Southern California. In the San Joaquin Valley they work only in groves near urban areas or with plenty of brown soft scale, which hosts the parasites when citricola scale is at the wrong stage.[1]
Pesticides
Most foliar sprays go on from late July through September, after egg hatch is complete, when the females have died and the small nymphs sit on outside leaves. UC IPM names acetamiprid, thiamethoxam, flupyradifurone and tolfenpyrad as the most effective. About 40% of San Joaquin Valley populations resist organophosphates, with likely cross-resistance to carbamates.[1]
In organic groves, petroleum oil sprays only suppress the scale, so several applications may be needed. Where Aphytis wasps are released against California red scale, growers can hold off broad-spectrum citricola sprays until Aphytis activity ends in fall.[1]
Common questions
- Why is citricola scale a problem in the San Joaquin Valley but not in Southern California?
- Parasitic wasps control it completely in Southern California. They are present in the San Joaquin Valley but do not control it there except in some groves near urban areas.[1]
- How do I tell citricola scale from brown soft scale?
- Citricola scale has one generation, so the nymphs on leaves are all about the same size and appear only in summer and fall. Brown soft scale has several generations, with every stage on leaves and twigs all year.[1]
- When is the best time to spray for citricola scale?
- Usually late July through September, after the eggs have finished hatching and the young scales are small and on the outer leaves.[1]
Sources
- University of California Statewide IPM Program, “Citricola Scale, UC IPM Pest Management Guidelines: Citrus.” ipm.ucanr.edu/agriculture/citrus/citricola-scale (accessed 2026-11-09)
- Entomological Society of America (Journal of Economic Entomology), “Grafton-Cardwell EE, Gu P, Daugherty MP. Impact of citricola scale Coccus pseudomagnoliarum (Hemiptera: Coccidae) on Valencia orange, Citrus sinensis production and fruit quality. Journal of Economic Entomology 115(6):2121-2124 (2022) (abstract).” doi.org/10.1093/jee/toac169 (accessed 2026-11-09)
- iNaturalist, “Coccus pseudomagnoliarum taxon page (order and family).” www.inaturalist.org/taxa/878358 (accessed 2026-11-09)