Cottony cushion scale
Cottony cushion scale is a sap-feeding scale insect. The female is orange-brown, and her white, fluted egg sac holds 600–800 red eggs, the two together about 1/2 inch long. It feeds on citrus, pittosporum, nandina and cocculus, and it drips honeydew that grows black sooty mould. In the 1880s it nearly wiped out California's young citrus industry, until the vedalia beetle, a small red-and-black lady beetle from Australia, was imported in 1888–89 and brought it under control within months. The beetle and a parasitic fly usually still keep it under control. Outbreaks usually mean something has killed them, most often an insecticide. Keep the natural enemies alive and the scale takes care of itself.
Icerya purchasi female with its fluted white egg sac, and a vedalia beetle feeding. Photo: pending.
Identification
The adult female is orange-brown. Once she starts laying, she pushes out an elongated, fluted white cottony egg sac. With the sac, she is about 1/2 inch (13 mm) long, and the sac holds 600–800 red eggs. Unlike most scales, cottony cushion scale keeps its legs and can move throughout its life.
Newly hatched nymphs are red with black legs and antennae. The long, fluted egg sac behind an orange-brown body is the thing to look for. Look on the sacs for oblong red eggs or red-and-black beetles. Those are the vedalia beetle at work.
Easily confused with
- MealybugsAlso a pestMealybugs have distinctly segmented bodies and older ones can still walk; the cottony cushion scale female carries a large white egg sac with fluted (ridged) sides.
- Cottony maple scaleAlso a pestA brown female with a cottony egg mass pushing out from her rear, found on maples (especially silver maple), honeylocust and linden rather than citrus.
- Cottony camellia scaleAlso a pestAn oval, yellow-tan cover with a brown rim, up to 1/8 inch (3 mm), with a white egg sac about 1/4 inch (6 mm) behind it, mostly under the leaves of camellia, holly and yew.
- Young vedalia beetle larvaeBeneficial — leave itReddish and oblong like the scale's crawlers and found on the egg sacs, but they have red legs and no obvious antennae; crawlers have dark legs and antennae.
Damage symptoms
Cottony cushion scale sucks sap and excretes honeydew, which is usually followed by black sooty mould and ants. When natural enemies are working, the damage is slight. In an outbreak, UC IPM reports leaf and fruit drop, dieback of twigs and small branches and, in extreme cases, defoliation and a severe fall in citrus yield. Cocculus laurifolius is often heavily infested and can decline.
- White, fluted egg sacs along twigs and on the undersides of leaves
- Sticky honeydew on leaves and fruit, then black sooty mould
- Ants running up the trunk
- Leaf and fruit drop, and twig dieback in heavy infestations
Lifecycle & degree days
Males are rare and females reproduce without mating, so a single scale can start a colony. The life cycle takes about three months in warm weather, with two to three generations a year in California. The vedalia beetle develops four times as fast and completes four generations for each one of the scale's. Adults and older larvae eat every stage of the scale; young larvae feed mainly on the eggs. Vedalia struggles in heat: UC notes that it stops laying eggs, and its larval development slows or halts, when daily temperatures exceed 90 °F. The parasitic fly Cryptochaetum iceryae is the more important of the two in coastal areas.
- Generation
- About 3 months in warm weather
- Generations / yr
- 2–3 (California)
- Eggs per female
- 600–800
- Vedalia generation
- 4–6 weeks in warm weather; egg-laying stops above 90 °F
Host crops
UC IPM names citrus, cocculus, nandina and pittosporum as the main hosts in California landscapes. Cocculus laurifolius is often highly infested. On citrus and most other hosts the scale is normally held under biological control, so an outbreak is a sign that the natural enemies have been knocked back.
Monitoring & action thresholds
The home-garden test is whether the natural enemies are present. Look for red vedalia eggs, larvae or adults on the egg sacs. The one numeric figure is for commercial citrus: UC IPM warrants a spray in June only if there are more than 4 live adult female scales per 2-foot branch. Its options there (buprofezin, malathion) are toxic to vedalia, and malathion is also toxic to bees, so it must not go on during bloom.
In early spring, March to April in California, look into the interior of the tree for adult females and their egg sacs, and check the sacs for vedalia eggs, larvae and adults. Ants on the trunk are a warning sign, because ants tending the honeydew fend off natural enemies. To time an oil spray, wrap double-sided sticky tape round infested twigs and watch for red crawlers.
Biological control
The vedalia beetle, Rodolia (now Novius) cardinalis, is the textbook case of classical biological control. By the 1880s the scale was killing trees in California's commercial citrus orchards. In the winter of 1888–89, 514 vedalia beetles were imported from Australia. (Two UC pest pages say the 1890s, but Cornell's dated account and UC's vedalia page put it in the 1880s.) Cornell's account records that they multiplied so fast that by June 12, 1889, officials were handing out 10,555 beetles to 208 growers. By autumn 1889 the scale was controlled wherever the beetle had been released. The project cost about $1,500. Vedalia is a lady beetle, about 1/8 inch (3 mm) long and red and black. It lays red eggs on the scale's egg sacs, and its larvae and adults eat every stage of the scale. A parasitic fly, Cryptochaetum iceryae, was also introduced from Australia and is the most important enemy near the coast. The catch is that vedalia cannot be bought: UC IPM says no commercial insectary rears vedalia, and the way to establish it is to collect beetles from another tree and move them. As few as 20 will found a population. The mealybug destroyer also eats soft-bodied insects that produce waxy egg sacs, but no trial against cottony cushion scale was found.
Cultural controls
Management is mostly about not getting in the vedalia beetle's way.
- Do not use imidacloprid on citrus with this scale: UC IPM says it does not kill cottony cushion scale but is very toxic to vedalia beetles
- Avoid broad-spectrum and persistent insecticides, especially from March to June when vedalia is most active
- Control ants climbing the trunk, and keep dust down. Both protect the scale from its enemies
- If no vedalia can be found by late March, collect some from an infested tree nearby and release them onto the egg sacs
- Prune out dense canopy, as UC IPM advises for commercial citrus
- If a spray is needed, use narrow-range horticultural oil on deciduous hosts in the dormant season, or on the foliage when crawlers emerge. It is the least disruptive to natural enemies and bees; keep drift out of water
Chemical, last resort
- Horticultural oil (narrow-range)REI 12 h
- BuprofezinREI 12 h
- ImidaclopridREI 12 h
- MalathionREI 72 h
Sources
UC IPM Pest Notes 7410, Cottony Cushion Scale (E.E. Grafton-Cardwell, 2012)
UC IPM Pest Management Guidelines: Citrus — Cottony Cushion Scale (updated 2017)
UC IPM Citrus PMG, Selectivity of Insecticides and Miticides (2022)
UC IPM Natural Enemies Gallery, Vedalia beetle
Cornell Univ., Biological Control guide: Vedalia beetle, Rodolia cardinalis (A. Shelton)
Bonide Horticultural & Dormant Spray Oil label, EPA Reg. 4-80 (2024)
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
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