Citricola Scale

Citricola Scale

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Description of the Pest

Citricola scale is a soft scale. Crawlers of the citricola scale appear from June through August. They settle primarily on the underside of leaves, but in severe infestations they also settle on the upper leaf surface and on twigs, rarely on fruit. Young scales are flat and almost translucent; they grow slowly over the course of the summer and fall, molting only once during that period. By November, second-instar scales turn a mottled dark brown color and begin migrating to twigs; this migration peaks in February and March. Once on twigs, they develop faster than they did on leaves and they turn a gray color. By late April, citricola scales molt and mature into the adult female stage. Females lay 1,000 to 1,500 eggs during the time from early May to early August. Eggs hatch after 2 to 3 days and crawlers move to leaves. There is only one generation a year, and there are no males.

Brown soft scale, another soft scale that is similar to citricola scale, may be found in the same areas as citricola scale but it has multiple generations and its colonies are composed of mixed instars and adults.


Citricola scale can be a serious pest of citrus in the San Joaquin Valley. A severe infestation may reduce tree vigor, kill twigs, and reduce flowering and fruit set. As they feed, citricola scales excrete honeydew, which accumulates on leaves and fruit. Sooty mold grows on honeydew and interferes with photosynthesis in leaves and causes fruit to be downgraded in quality during packing.


Citricola scale is completely controlled by Metaphycus and Coccophagus parasites in Southern California and is almost never seen. Even though these parasites are established in the San Joaquin Valley, biological control is not effective there, and insecticide applications may be necessary in groves where broad-spectrum pesticides are not regularly used to control other pests. In groves practicing biologically based pest management (e.g., releasing Aphytis melinus for California red scale control), growers may consider withholding broad-spectrum citricola sprays until Aphytis activity is over in the fall (e.g., late October or November).

Biological Control

Introduced and indigenous parasitic wasps, Metaphycus luteolus, M. stanleyi, M. nietneri, M. helvolus, and Coccophagus spp., control citricola scale in Southern California. Several of these parasites occur in the San Joaquin Valley but are unable to control citricola scale except in groves near urban areas or in those with high numbers of brown soft scale, which serves as an alternate host for the parasites when citricola scales are not in the stage that the parasite attacks.

Organically Acceptable Methods

Use biological control and organically approved petroleum oil sprays, such as 440 oil PureSpray Green in organically managed orchards. Oils alone only suppress citricola scale so multiple applications may be required.


Oil is the most selective pesticide available for control of citricola scale. However, oil simply reduces the scales’ overall numbers and in many cases must be applied 1 or 2 times every year. The organophosphate malathion and the carbamate carbaryl (Sevin) are broad-spectrum and toxic to most natural enemies. The neonicotinoids thiamethoxam (Actara) and acetamiprid (Assail) are fairly broad-spectrum (i.e., toxic to most natural enemies). The insect growth regulator buprofezin (Centaur) is a fairly selective pesticide, but it does affect vedalia beetles.


IIn the San Joaquin Valley, 40% of populations of citricola scale have been found to be resistant to organophosphate insecticides. There is likely cross-resistance to carbamates. Thus, low rates of these insecticides would be ineffective, and high rates only suppress citricola scale for a single year. Growers experiencing resistant scale should use other insecticides (buprofezin, thiamethoxam, or acetamiprid).

Monitoring and Treatment Decisions

Citricola scale is only a problem in the San Joaquin Valley. It is very sensitive to organophosphates and carbamates (if not resistant) and generally does not become a problem until growers stop using these insecticides for control of other pests. Check for citricola scale at all times of the year when monitoring for other scales, but look especially closely at the twigs in April and at the underside of leaves in late July.

Be sure to distinguish the citricola scale from brown soft scale. Brown soft scale has multiple generations and all stages will be present on leaves and twigs year round, whereas citricola scale has only one generation and is found on leaves only in the summer and fall, and the nymphs will be uniform in size.

April-May Sampling

Examine one 24-inch twig on the northeast side of 10 trees in each of four rows (for a total of 40 twigs) distributed throughout the orchard. On each twig count the number of scales and determine the average number of scales by dividing the total number in the sample by 40. If there is more than an average of one scale per twig and heavy production of sooty mold is occurring, the orchard may require an immediate pesticide application. If the population on twigs or leaves is observable but sooty mold is not a problem, then it is best to postpone pesticide application until fall when scales are small, positioned on leaves on the outside of the tree, and generally easier to control.

July-September Sampling

To sample for citricola scale in summer:

  1. Walk down four evenly spaced rows of the block.
  2. In each row, pick one leaf from the northeast side of 25 trees.
  3. Examine the scale on the underside of the leaf to determine if they are alive or dead.
  4. Count the number of leaves in the 25-leaf sample that are infested with live scale (presence-absence sampling). Record results (example form— PDF )

A spray is warranted if one or more of the four rows has five or more leaves infested with live citricola scale in a 25-leaf sample. If four or fewer leaves are infested, then a pesticide application could wait until the following season. Alternatively, count the number of nymphs on those 100 leaves (4 rows x 25 leaves) and if there are more than 0.5 nymphs per leaf then treatment is needed.

Treatment Timing and Relative Efficacy

Acetamiprid (Assail), thiamethoxam (Actara) and flupyradifurone (Sivanto) are the most effective insecticides for citricola scale control.

Spring Treatments

Assail and Actara are the only insecticides effective against adult scales in spring before petal fall. However, they are fairly broad-spectrum and at this time of year only suppresses the females. Thus, they should not be used unless there is a severe problem that cannot wait until a summer treatment.

Summer through Fall Treatments

Most foliar insecticides are applied during late July through September because at that time of year the female scales have died, the nymphs are small and located on the outside leaves of the tree, and temperatures are warm, which makes the insecticides more effective. Monitor eggs under the adult females during June and July and apply the insecticide after hatch is completed.

See also:  How to Get Rid of Bugs and Midges in the Yard, Hunker

About 40% of populations of citricola scale in the San Joaquin Valley have been determined to have resistance to organophosphate insecticides. Avoid malathion, dimethoate, or cabaryl insecticides if resistance is known to be a problem. The insect growth regulator buprofezin (Centaur) is fairly selective (toxic only to vedalia beetles) and will suppress citricola scale during the season that it is applied. The foliar neonicotinoids thiamethoxam (Acatara) and acetamiprid (Assail) and flupyradifurone (Sivanto) are fairly broad-spectrum and will control citricola scale for 1 to 2 years. Foliar neonicotinoids are more effective against citricola scale than systemic neonicotinoids. Citricola scale populations grow more rapidly and survive the summer better when the San Joaquin Valley experiences a cool, wet spring. When these conditions occur, the higher rates, careful spray coverage of the tree, and properly timed applications (late July to early August, when eggs have completely hatched and the nymphs are small) are most effective.

Common name Amount to use REI‡ PHI‡
(Example trade name) (type of coverage)** (hours) (days)
Pesticide precautions Protect water Calculate VOCs Decision support Protect bees
Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide’s properties and application timing. Always read the label of the product being used.
(Centaur WDG) 34.5–46 oz/acre (TC) 12 3
RANGE OF ACTIVITY: Pests: narrow (scales, whiteflies); Natural enemies: predatory beetles
PERSISTENCE: Pests: intermediate; Natural enemies: intermediate
COMMENTS: Slow-acting; this product does not kill the scale until they molt, so decline in scale numbers is usually not observed for several months.
. . . PLUS . . .
(415) 0.5–1% See label See label
RANGE OF ACTIVITY: Pests: broad (unprotected stages of insects and mites); Natural enemies: most
PERSISTENCE: Pests: short; Natural enemies: short
MODE OF ACTION: Contact including smothering; also improves insecticide spread and persistence.
(Assail 70WP) 3.4–5.7 oz/acre (IC or TC) 12 7
RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most
PERSISTENCE: Pests: intermediate; Natural enemies: intermediate
COMMENTS: Effective against both adults and nymphs. Residues last for 4 to 6 weeks. Apply in 300 to 1000 gal water/acre; use higher volume if insects are inside the canopy on the wood. Toxic to vedalia beetle and should not be used in cottony cushion scale-infested orchards.
(Actara) 5.5 oz/acre 12
RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most
PERSISTENCE: Pests: intermediate; Natural enemies: long
COMMENTS: Effective against both adults and nymphs. Residues last for 4 to 6 weeks. Apply in 300 to 1000 gal water/acre; use higher volume if insects are inside the canopy on the wood.
(Sivanto 200SL) 12–14 fl oz/acre (IC) 12 1
RANGE OF ACTIVITY: Pests: sucking insects such as psyllids, soft scales and aphids; Natural enemies: parasitic wasps
PERSISTENCE: Pests: short; Natural enemies: short
COMMENTS: Safe for bees, and can be used during bloom. Do not exceed 28 fl oz Sivanto (0.365 lb a.i. flupyradifurone)/acre per year.
(Malathion 8 Flowable) 7.5 pt/acre (IC or TC) 72 7
RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most
PERSISTENCE: Pests: intermediate; Natural enemies: intermediate
COMMENTS: For use on all varieties. Do not apply during bloom.
RESISTANCE: 40% of San Joaquin Valley populations are resistant to organophosphate insecticides.
(Sevin XLR Plus) 3–5 qt/acre (IC or TC) See label 5
RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most
PERSISTENCE: Pests: long; Natural enemies: long
RESISTANCE: 40% of San Joaquin Valley populations are resistant to organophosphate insecticides.
. . . PLUS . . .
(415) 0.5–1.4% See label See label
RANGE OF ACTIVITY: Pests: broad (unprotected stages of insects and mites); Natural enemies: most
PERSISTENCE: Pests: short; Natural enemies: short
MODE OF ACTION: Contact including smothering effects; also improves insecticide spread and persistence.
(415, 435, 440) 1.2–1.4% (IC or TC) See label See label
RANGE OF ACTIVITY: Pests: broad (unprotected stages of insects and mites); Natural enemies: most
PERSISTENCE: Pests: short; Natural enemies: short
MODE OF ACTION: Contact including smothering effects.
COMMENTS: For use on grapefruit, lemons, navels, Valencias. Use higher rate for July or August applications only. To avoid phytotoxicity, use same spray timings as given for oil sprays for California red scale in Central California. Narrow range 440 (or higher) spray oil is preferable in the Central Valley during warmer months because of greater persistence, but risk of phytotoxicity increases unless using products with 99% unsulfonated residues (UR). Do not apply oil until hatch is complete (late July to early August). Caution: Serious hazards are associated with oil sprays to green lemons because of phytotoxicity after sweating; check label for preharvest interval. Oils alone only suppress citricola scale, so they may need to be applied multiple times.
** IC — Intermediate coverage uses 250 to 600 gal water per acre.
TC — Thorough coverage uses 750 to 2,000 gal water (or more)/acre, depending on tree size.
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
* Permit required from county agricultural commissioner for purchase or use.
1 Rotate chemicals with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; chemicals with a 1B group number should be alternated with chemicals that have a group number other than 1B. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee).

Important Links

UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441

E.E. Grafton-Cardwell, Lindcove Research and Extension Center, Exeter and Entomology, UC Riverside

J.G. Morse (emeritus), Entomology, UC Riverside (emeritus)

D.R. Haviland, UC IPM and UC Cooperative Extension Kern County

B.A. Faber, UC Cooperative Extension Ventura County

Acknowledgement for Contributions to Insects, Mites, and Other Invertebrates

J. Barcinas, E.S.I., Corona

R. Dunn, Badger Farming Co., Exeter

J. Gorden, Pest Management Associates, Exeter

C.E. Kallsen, UC Cooperative Extension Kern County

D. Machlitt, Consulting Entomology Services, Camarillo

C.H. Musgrove, UC Citrus Research Center and Agricultural Experiment Station, Riverside

K. Olsen, S & J Ranch, Pinedale

N.V. O’Connell, UC Cooperative Extension Butte County

P.A. Phillips (emeritus), UC Cooperative Extension Ventura County

T. Roberts, PCA, Integrated Consulting Entomology, Ventura

T. Shea, UC Cooperative Extension Riverside County

J. Stewart, Pest Management Associates, Exeter

P. Washburn, Washburn & Sons Citrus Pest Control, Riverside

Scale Insects

Scale are tiny sap sucking insects with protective coverings that can be found attached to plant leaves and stems.

Identify the problem

Scale are sap sucking insects that have protective coverings. The protective coverings can be hard and waxy to soft and foam-like. The shield like protective cover or frothy covering can make it difficult to identify them as insects. Scales are commonly brown, black, grey or white. See the gallery for some examples.

Scale insects fix themselves to leaves and stems and suck sap. Their waste products are a sweet honeydew that ants and wasps will feed on readily. The sticky honeydew will also encourage moulds such as sooty mould. It may be difficult to see the scale if they are covered by the mould. Infested leaves usually turn yellow. Some scale live beneath bark and are not easily seen.


To Get Rid of Scale Insects:

  • Scale insects can be difficult to get rid of but spraying with PLANThealth Spectrum and/or Organic Insect Control followed by Organic Super Spraying Oil is most effective, killing scale through suffocation. However, do not spray in the middle of the day or in strong sunlight or high temperature as this can cause burning of the plant. It is best to apply to the crawling and young stages of scale insect.
  • Once control has been achieved PLANThealth Spectrum is a good option for prevention and control of scale and the mould that often accompanies them. They can also be applied before (at least one day) application of Organic Super Spraying Oil.


Control Ants and the Sap Sucking Insects they ‘Farm’ in Trees, Shrubs and Ornamantals

  • Apply LawnPro Protect on the the soil around the roots of affected plants. This kills and prevents ants moving up the plants, and is systemic and taken up by the roots of the plant to control the sap sucking scale and other insects directly.

Did You Know

There are many species of scale insect in the family Coccoidea. In New Zealand common pest species include:

  • San Jose Scale — Quadraspidiotus pemiciosus
  • Rose scale — Aulacaspis rosae
  • Oystershell scale — Quadraspidiotus ostreaeformis
  • Soft brown scale — Coccus hesperidum
  • Apple mussel scale — Lepidosaphes ulmi
  • Greedy scale — Hemiberlesia rapax
  • Cottony cushion scale— Icerya purchasi
  • Juniper scaleCarulaspis juniperi
  • Brown scaleParthenolecanium corni

How to Manage Pests

Pests in Gardens and Landscapes

Black Scale

In this Guideline:

Black scale adult with “H” ridge and third-instar nymph at rubber stage.

Black scales and honeydew.

Black scale crawler and eggs.

Heavy scale infestation on an olive branch.

A parasitic wasp, Scutellista caerulea, emerging from a scale and two scales with exit holes.

Black scale, Saissetia oleae, is a soft scale insect native to southern Africa that is currently an agricultural and horticultural pest in southern Europe, North America, South America, Asia, Australia, and New Zealand. In North America, the insect is distributed in the southern and western United States as well as in Mexico and Central America. The insect was introduced to California before 1880 and has since become an economic pest primarily on olive, but it can also cause damage on citrus. Black scale is one of the more damaging soft scale pests in California and can be found on numerous hosts including almond, apple, apricot, aspen, bay, citrus, cottonwood, coyote brush, fig, fuchsia, grape, holly, maple, oleander, olive, palm, peppertree, pistachio, plum, pomegranate, poplar, privet, prune, rose, and strawberry tree.


The adult female black scale is the easiest of the life stages to identify based on size, shape, and color. Adult females are the largest of the life stages, with a body measuring up to 1/5 inch long and 1/8 inch wide. They are dark brown to black, convex in shape, and have a distinctive H-shaped ridge on their back. Black scale infestations are often associated with sooty mold fungus because the insect exudes sticky carbohydrate-rich honeydew on the plant surface that serves as a substrate for fungal growth. Because the first- and second-instar nymphs are sensitive to hot, dry conditions, black scale is more common in coastal regions or on trees with dense canopies that foster a cooler, more humid microclimate than found in the interior valleys.


Black scale has either one or two generations per year depending on climate. For example, in coastal California climates, black scale has two generations per year. In the inland areas of Southern California and in the San Joaquin Valley, the insect has only one generation per year, although a partial second generation can be found as well, especially in trees with dense canopies.

Although black scale males are known to occur, they have never been recorded in California and reproduction is parthenogenic, meaning the female black scale adult doesn’t have to mate with a male to produce offspring. Mature females may produce more than 2,000 eggs each, and the egg color changes from pale yellow to orange as the eggs mature. Eggs are laid directly under the adult female body, and the subsequent egg hatch may take several weeks to complete.

First-instar nymphs (called “crawlers” until they settle and start to feed) are pale yellow to light brown and only 1/64 inch long, making them difficult to detect without a hand lens. After hatching from eggs, crawlers may spend up to seven days searching for a feeding site, typically on foliage. Black scales go through two more immature stages, or instars, before becoming adults, molting or shedding the cuticle between each stage. In the interior valleys, where there is one generation per year on olives, egg hatch is typically in May. The first molt occurs in the summer, around three to eight weeks after hatching, depending on temperature and host plant condition. There is little development during the summer, as summer heat hampers the scale’s development and survival. For this reason, the second molt often occurs around two and a half to three months after egg hatch, revealing the third instar, a sexually immature adult.

Soon after the second molt, the third-instar nymphs tend to migrate from leaves to twigs, where they will typically overwinter. In spring, the late third instar begins to enlarge as her ovaries develop and is then commonly referred to as the “rubber stage.” The rubber stage is 1/16 to 1/5 inch long, is ash gray to brown, and has a distinct H-shaped ridge on its back. By April most black scales have progressed to the rubber and adult stages. This is the period of rapid growth and when most honeydew is produced. The adult female’s coloration changes from dark brown to black as she matures.


Black scale can adversely affect plant vigor and productivity. The impact on productivity is perhaps most evident in olive trees where heavy scale infestations may reduce return bloom and the size of next year’s crop. Additionally, sooty mold colonization of honeydew deposits may reduce the plant’s photosynthetic activity by effectively shading leaf surfaces from the sun, resulting in some defoliation. Honeydew and sooty mold detract from the aesthetic value of landscape plants and render harvest of fruit an unpleasant activity due to the sticky nature of the honeydew. In commercial orchards, sooty mold infestation may result in downgraded fruit quality. The honeydew may also attract tephritid fruit flies (i.e., olive fruit fly) and vinegar flies (i.e., Drosophila species) as well as other insects such as wasps and ants that use the honeydew as a food source.


Management of black scale in the home landscape may be approached with combined cultural, biological, and chemical control strategies. In many cases biological control is sufficient unless broad-spectrum sprays for other pests have killed natural enemies. Few home gardeners in most parts of California need to spray for black scale.

Cultural Control

Because the second- and third-instar nymphs are susceptible to desiccation (extreme dryness), pruning the plant canopy may eliminate cool microclimates that promote black scale survival. If possible, prune out infested branches of the plant to physically reduce black scale populations on site. Pruning is the best cultural control practice available both in commercial orchards and in home landscapes. Hand removal or crushing of scales on individual plants can also be an effective management tool in the landscape.

Biological Control

Efficacy of biological control for management of black scale may vary by region. In the southern San Joaquin Valley, biological control of black scale may be ineffective because the timing of the scale life cycle isn’t conducive to insect parasitoid reproduction and development. However, in Northern California and the state’s coastal areas, a number of parasitoids (tiny wasps, barely visible to the naked eye) may attack black scale, including Scutellista caerulea and Metaphycus helvolus, providing effective control in many landscapes. The presence of resident natural enemies in landscapes can be determined by observing mature female scales with a hand lens. Parasitized scales will have a small exit hole chewed by the adult parasite. To protect resident natural enemies, avoid using broad-spectrum persistent insecticides in landscapes.

Biological control of soft scales can often be inhibited by the activities of ants, which protect them from natural enemies. If ants are active, manage them by circling trunks with a sticky material such as Tanglefoot placed on trunk wraps, and prune to prevent bridges between plants that may allow ants to move from the ground or infested plants to vegetation above the sticky barrier. Ant baits may also be effective.

Chemical Control

A narrow-range mineral oil, applied at high spray volumes (beyond the point of runoff), may be utilized to manage black scale. A recent study also suggests that canola oil (1% by volume) may be utilized as a nonpetroleum-based product to manage black scale on olive. Oil essentially suffocates the insect and is most effective at the crawler stage (early first instar); therefore, monitoring of the insect population is essential for successful control. Because black scale attacks a diverse range of host plants, it is important to consider the potential for oil applications to cause phytotoxicity (damage to plants). Before widespread use in a landscape, test for potential phytotoxicity by applying oil to a small group of plants or plant parts.

If scale populations are high and there are few signs of parasitization, an oil application may be employed to manage black scale. In the San Joaquin Valley, a winter oil application may be effective when applied between November and late January—a timeframe when the rubber stage and adult insects aren’t generally present. In both the Sacramento Valley and the San Joaquin Valley, a summer oil application may be applied when crawlers have hatched, generally from mid-May through August. To properly time a summer oil application, double-sided sticky traps can be suspended in the tree canopy to monitor for presence of crawlers. Oil applications must be completed before the insect enters the rubber stage or adult stage; thereafter, applications aren’t effective. For more information about managing scales, see Pest Notes: Scales.


Alford, D. V. 2007. Pests of Fruit Crops: A Color Handbook. Boston: Academic Press.

Daane, K. M., R. E. Rice, F. G. Zalom, W. W. Barnett, and M. W. Johnson. 2004. Arthropod Pests of Olive. In G. S. Sibbett and L. Ferguson, eds. Olive Production Manual, 2nd ed. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 3353. pp. 204–213.

Dreistadt, S. H., J. K. Clark, and M. L. Flint. 2004. Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, 2nd ed. Univ. Calif. Agric. Nat. Res. Publ. 3359.

Nicetic, O., Y. R. Cho, and D. J. Rae. 2011. Impact of physical characteristics of some mineral and plant oils on efficacy against selected pests. J. of App. Ent. 135:204–213.

Quayle, H. J. 1941. Insects of citrus and other subtropical fruits. Ithaca, N.Y.: Comstock Publishing Company Inc.

Sibbett, G. S., J. E.,Dibble, and J. D. Babcock. 1976. Black scale now a major olive pest. Calif. Ag. 30:12–13.

Wang, X.-G., M. W. Johnson, S. B. Opp, R. Krugner, and K. M. Daane. 2011. Honeydew and insecticide bait as competing food resources for a fruit fly and common natural enemies in the olive agroecosystem. Entomol. Exp. et Appl. 139:128–137.


Pest Notes: Black Scale
UC ANR Publication 74160

Authors: E. J. Fichtner, UC Cooperative Extension, Tulare Co.; and M. W. Johnson, Cooperative Extension Specialist and Entomologist, UC Riverside.

Produced by UC Statewide IPM Program, University of California, Davis, CA 95616

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Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2019 The Regents of the University of California. All rights reserved.

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