SCALES

Integrated Management for Home Gardeners and Landscape Professionals

Scale can be serious pests on all Female soft scales, family , types of woody plants and shrubs. may be smooth or cottony and have a Scales are so unusual looking that diameter of 1⁄4 inch or less. They are many people do not at first recognize usually larger and more rounded and them as insects. Adult female scales convex than armored scales. The sur- and many immature forms do not face is the actual body wall of the in- move, are hidden under a disklike or sect and cannot be removed. Most waxy covering, and lack a separate immature soft scales retain their barely head or other recognizable body parts. visible legs and antennae after settling Scales have long piercing mouthparts and are able to move, although slowly. with which they suck juices out of Soft scales produce large quantities of plants. They may occur on twigs, honeydew, which is modified plant leaves, branches, or fruit. Severe infes- sap, that drips from their bodies. Ex- tations can cause overall decline and amples of soft scales are black scale, even death of plants. Most scales have brown soft scale, and European fruit Figure 1. Armored scale infestation on many natural enemies that often effec- lecanium. twig. tively control them. LIFE CYCLE Armored scales and soft scales are the Most armored scales have several gen- cycles and stages for scales are out- most common types of scales on erations a year, while most soft scales lined in Figures 2 and 3. woody plants. Common scales in each (brown soft scales are an important group as well as several other types of exception) often have only a single DAMAGE scales that are important on specific generation. Eggs of both types of scales Woody plants heavily infested with host plants are listed in Table 1. Excel- are usually hidden under the adult armored scales often look water lent color keys for scale insects in Cali- female. Eggs hatch into tiny, usually stressed. Leaves may turn yellow and fornia are available from the California yellow crawlers with legs. Crawlers drop, twigs and limbs on trees may Department of Food and Agriculture; walk over the plant surface, are blown die, and bark may crack and produce see “References” for titles. by wind to other trees, or can be inad- gum. Many armored scales attack vertently moved by people or birds. leaves or fruit as well, leaving blem- IDENTIFICATION Armored scales settle down perma- ishes and halos on fruit; the fruit dam- Armored scales, family Diaspididae, nently after a day or two in the crawler age is often just aesthetic. Some are less than 1/8 inch in diameter and stage, molt, and begin to form their armored scales can kill plants. have a platelike cover (Fig. 1). This characteristic covers. Soft scales move cover usually can be removed from the around for a while longer but also Soft scales also reduce tree vigor but scale body. They are called armored eventually settle at permanent feeding seldom kill trees. The major concern scales because the scale cover is quite sites; half-grown individuals of some with these scales is their production of dense and provides a degree of protec- soft scale species move once again in abundant quantities of honeydew, tion from and parasites. The fall from leaves to wood for overwin- which gets on leaves and fruit, armored scales hatch from eggs, settle tering. Adult female scales are immo- encouraging the growth of black sooty down, lose their legs, and form a hard bile and have a characteristic scale mold. Honeydew also attracts ants, cover that is usually separate from the cover. Adult male scales are tiny which protect soft scales from natural scale’s body. Armored scales do not winged insects that superficially re- enemies; the presence of ants on a tree excrete honeydew. Examples of ar- semble parasitic wasps. They are rarely or shrub is a good indication of an mored scales include California red seen, do not feed, and live only a few infestation by a honeydew-producing scale, greedy scale, oystershell scale, hours. Females of many soft scale spe- . Soft scales infest leaves and and . cies reproduce without mating. Life twigs and do not attack fruit directly.

PEST NOTES Publication 7408 University of California Agriculture and Natural Resources Revised April 2001 April 2001 Scales

TABLE 1. Some Common Scales Found in California and Their Principal Hosts

Common Scales Principal Hosts

Armored Scales California red scale () acacia, boxwood, , eugenia, euonymus, grape, magnolia, mulberry, olive, palm, podocarpus, privet, rose cycad scale (Furchadaspis zamiae) bird-of-paradise, cycads (sago palm) euonymus scale (Unaspis euonymi) euonymus greedy scale (Hemiberlesia rapax) acacia, bay, boxwood, cactus, ceanothus, citrus, fruit trees, holly, laurel, magnolia, man- zanita, palm, pepper tree, pittosporum, pyracantha, redbud latania scale (Hemiberlesia lataniae) acacia, Cedrus, euonymus, Fatsia, fuchsia, gladiolus, grevillea, Hedera helix, Kentia, persea, philodendron, rose, Rubus, Salix, yucca minute cypress scale (Carulaspis minima) arborvitae, cypress, juniper oleander scale (Aspidiotus nerii) acacia, bay, boxwood, cactus, holly, ivy, laurel, magnolia, manzanita, maple, mulberry, oleander, olive, palm, pepper tree, redbud, sago palm, Taxus (yew), yucca oystershell scale (Lepidosaphes ulmi) alder, aspen, box elder, boxwood, ceanothus, cottonwood, most deciduous fruit and nuts, holly, maple, poplar, sycamore, willow purple scale (Lepidosaphes beckii) citrus San Jose scale (Quadraspidiotus perniciosus) acacia, aspen, citrus, cottonwood, most deciduous fruits and nuts, maple, mulberry, poplar, pyracantha, rose, strawberry tree, willow walnut scale (Quadraspidiotus juglansregiae) walnut

Soft Scales black scale (Saissetia oleae) almond, apple, aspen, bay, citrus, cottonwood, coyote bush, fig, holly, maple, mayten, oleander, olive, palm, pear, pepper tree, pistachio, poplar, privet, stone fruit, strawberry tree, walnut brown soft scale ( hesperidum) aspen, avocado, citrus, cottonwood, holly, manzanita, palm, poplar, stone fruit, straw- berry tree, willow calico scale (Eulecanium cerasorum) box elder, liquidamber, maple, pear, stone fruit, walnut citricola scale (Coccus pseudomagnoliarum) citrus, elm, hackberry, pomegranate, walnut European fruit lecanium (Parthenolecanium alder, almond, aspen, cottonwood, elm, grape, pear, pistachio, poplar, stone fruit, toyon, corni) (also called brown apricot scale) walnut frosted scale (Parthenolecanium pruinosum) ash, birch, elm, laurel, locust, pistachio, rose, sycamore, walnut green shield scale (Pulvinaria psidii) begonia, California pepper tree, camellia, croton, eugenia, gardenia, hibiscus, laurel fig or Indian laurel (Ficus retusa), pittosporum, plumeria, Schefflera irregular pine scale (Toumeyella pinicola) pine Kuno scale (Eulecanium kunoense) cotoneaster, pyracantha, stone fruit, walnut tuliptree scale (Toumeyella liriodendri) deciduous magnolias, gardenia, linden, tuliptree (yellow poplar) wax scales, including barnacle and California bay laurel, citrus, coyote bush, gardenia, holly Chinese wax scales (Ceroplastes spp.)

Other Scales cottony cushion scale1 (Icerya purchasi, citrus, cocculus, nandina, pittosporum family Margarodidae) European elm scale (Gossyparia spuria, elm, especially Chinese elm family Eriococcidae) oak pit scales2 (Asterolecanium spp., oak family Asterolecaniidae) sycamore scale3 (Stomacoccus platani, London plane, sycamore family Margarodidae)

1 See Pest Notes: Cottony Cushion Scale, UC DANR Publication 7410 2 See Pest Notes: Oak Pit Scales, UC DANR Publication 7470 3 See Pest Notes: Sycamore Scale, UC DANR Publication 7409

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MANAGEMENT on honeydew produced by scales or plant. Prune to open up tree canopies Scales are often well controlled by other insects that suck plant juices. in warm-climate areas, such as the natural enemies, especially when Central Valley of California. This in- predator and parasite activities are not Cultural Control creases scale mortality resulting from disrupted by ants or applications of Provide plants with good growing heat exposure and helps to control broad-spectrum insecticides such as conditions and proper cultural care, black scale and possibly other scale carbaryl, malathion, or pyrethroids especially appropriate irrigation, so species. applied to control other pests. If scale they are more resistant to scale dam- populations, especially armored scale age. Prune off heavily infested twigs Biological Control species, become abundant, you should and branches to eliminate scales when Scales are often controlled by natural take action. In the case of soft scales, infestations are on limited parts of the enemies, including many species of controlling ants may be sufficient to bring about gradual control of scales as natural enemies become more abun- dant. If not, well-timed sprays of oil Figure 2. Life stages of a typical armored scale, the California red scale. applied either during the dormant season or when crawlers are active in spring (or, in the case of black scale, in summer) should provide good control.

Monitoring Monitor scales by inspecting plants for crawlers, mature females, or ants. Dead second-instar virgin female gravid female scales from previous generations can female adult (underside) remain on plants and it is important to distinguish live scales from dead ones. crawler white cap On landscape plants, action thresholds nipple stage have not been established for scales. Develop thresholds for your local situ- ation. Monitor and record scale densi- first instar ties and use the density that caused damage (dieback or unacceptable hon- eydew) as your preliminary control second-instar third- and fourth-instar action threshold. Refine this threshold male male (underside) male adult over time as you gain experience.

Examine deciduous plants when leaves are gone in winter. Armored scales overwinter primarily as first-instar nymphs and adult females, whereas Figure 3. Life cycle of a typical soft (family Coccidae). soft scales commonly overwinter as mature females second-instar nymphs. On deciduous crawlers trees and bushes, twigs and branches heavily infested with scales may retain eggs their leaves during winter and be easy beneath female scale to spot. Citrus, avocado, and other plants that do not enter a winter dor- mancy can be monitored by examining leaves, twigs, limbs, and fruit for evi- dence of a scale infestation. settled first females before instars During the growing season, inspect egg laying trunks for ants, which may indicate a soft scale infestation. If the descending second instars on twig ants have swollen, almost translucent abdomens, they are probably feeding

N 3 N April 2001 Scales small, dark, lady . Hyperaspis Ant Control problems from their runoff in urban species are tiny, shiny, black lady If large numbers of ants are climbing surface water and contamination of beetles with several red, orange, or up trunks to tend scales they should municipal wastewater. yellow spots on the back. Rhyzobius be controlled. Deny ants access to lophanthae is a lady that has a plant canopies by pruning branches Oil Precautions. Don’t apply oils dur- reddish head and underside, and a that provide a bridge between build- ing the fog or rain, or during or before grayish back densely covered with tiny ings or the ground and by applying a hot or freezing weather (over 90°F or hairs. The twicestabbed lady beetle, sticky material (such as Tanglefoot or under 32°F). Do not apply oils to decidu- orbus, is shiny black with Stikem) to trunks. If trees are young, ous trees within 30 days before or after two red spots on its back, and reddish thin-barked, or recently pruned, wrap applications of sulfur, captan, or certain underneath. The larvae of certain pre- the trunk first with a strip of fabric other fungicides to avoid damage to trees. daceous lady beetles can be found un- tree wrap, duct tape, or another mate- der the female soft scales feeding on rial to prevent injuring the tree. Alter- Spring/Summer Treatments. Dormant scale eggs and crawlers. natively, or as a supplement, place season applications of oils are not ap- enclosed baits such as ant propriate for scales on citrus or avo- Many parasitic wasps are important stakes near nests or on ant trails be- cado because these trees do not enter a natural enemies of scales, including neath plants. winter dormancy; oils are best applied species of Aphytis, Coccophagus, Encar- to these trees in spring or summer. sia, and Metaphycus. Estimate parasite Chemical Control Horticultural oils can also be used in activity by checking scale covers for Dormant Treatments. Dormant- spring or summer against scale crawl- the round exit holes made by emerging season applications of specially re- ers on deciduous plants. Treatment at adult parasites. Remove the covers of fined oils, often called narrow-range, this time requires more spray volume armored scales and examine beneath supreme, or superior type oils, are than a dormant treatment because foli- them for immature parasites. Grow effective against most scale pests of age as well as bark must be thoroughly flowering plants near scale-infested deciduous trees and landscape plants, covered. Spring or summer applica- trees and shrubs to help augment natu- especially San Jose scale, walnut scale, tions must be carefully timed to reach ral enemies. Adult parasitic wasps live and the lecanium scales, but not crawlers, which are the most suscep- longer, lay more eggs, and kill more against oystershell or olive scales be- tible stage. Use traps made of double- scales when they have nectar or honey- cause susceptible stages of these pests sided sticky tape to determine when dew to feed on. are not present during winter. Avoid crawlers are hatching. Before crawlers oils called dormant oil or dormant oil begin to emerge in spring, tightly en- Dust control is crucial to the success of emulsions, which are more likely to circle several twigs or branches on the biological control. Wash plant surfaces injure plants. Treatments can be made infested tree with transparent tape that midseason, or when the foliage is any time during dormancy or, for is sticky on both sides (this tape is dusty, to encourage biological controls. sycamore scale and oak pit scales, available at stationery stores). Change during the delayed dormant period, the tapes at regular intervals, about Natural enemies are commercially which is the time after the buds swell weekly, and examine the tapes with a available for release against black scale but before they open. Be sure that the hand lens to identify the crawlers. and California red scale. However, plants are not water stressed to avoid Once eggs begin hatching, scale crawl- conserving resident natural enemies is injury. A good time to apply oils is ers get stuck on the tapes and appear a more efficient and longer lasting right after a period of rain or foggy as yellow or orange specks. strategy than buying and releasing weather. them, particularly in garden situations. If a spring or summer foliar insecticide An application of oil or soap alone is application is planned, spray after a Depending on the scale species and the usually adequate. One study (of syc- sharp increase in crawler production extent to which biological control has amore scale) found that organophos- occurs or after crawler numbers have been disrupted, it may take several phates (e.g., malathion) combined peaked and begin to decline. For more months of conservation efforts before with oil were no more effective than a information on sticky tape monitoring, scale populations are reduced by bio- properly timed, thorough application consult Pests of Landscape Trees and logical control. If current levels of of oil or soap alone. Shrubs, listed in the “Compiled From” scales are intolerable, use a short re- section. sidual insecticide such as oil or soap to Avoid using the organophosphates reduce scale populations while con- chlorpyrifos (Dursban) and diazinon In addition to narrow-range oil, insecti- serving natural enemies. in landscapes and gardens because of cidal soap and carbamate insecticides

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are registered as foliar sprays for scale COMPILED FROM control. Foliar sprays of the more per- Gill, R. J. 1982. Color-Photo and Host Keys Flint, M. L. 1998. Pests of the Garden to the Soft Scales of California. Scale and sistent, broad-spectrum insecticides and Small Farm: A Grower’s Guide to Whitefly Key #4. Sacramento: Calif. Dept. (carbamates) cause greater disruption Using Less Pesticide, 2nd ed. Oakland: Food Agric. of biological control than oil or soap Univ. Calif. Agric. Nat. Res. Publ. treatments because persistent residues 3332. Gill, R. J. 1988-1997. The Scale Insects of continue to kill natural enemies mi- California Parts 1–3. Sacramento: Calif. grating in after the application. Flint. M. L., and S. H. Dreistadt. 1998. Dept. Food Agric. Natural Enemies Handbook: The Illus- Soil applications of imidacloprid trated Guide to Biological Pest Control. UC Statewide IPM Project. Mar 2000. (Bayer Advanced Garden, Marathon, Oakland: Univ. Calif. Agric. Nat. Res. Pest Notes: Cottony Cushion Scale. Oak- Publ. 3386. Merit) will provide long-term control land: Univ. Calif. Agric. Nat. Res. Publ. of soft scales but not armored scales. 7410. Also available online at Dreistadt, S. H., J. K. Clark, and M. L. www.ipm.ucdavis.edu Additional insecticides are available to Flint. 1994. Pests of Landscape Trees and licensed pest control applicators for Shrubs: An Integrated Pest Management UC Statewide IPM Project. Mar 2000. Pest use in landscape plantings. In addition, Guide. Oakland: Univ. Calif. Agric. Notes: Oak Pit Scales. Oakland: Univ. Ca- the insect growth regulators Nat. Res. Publ. 3359. lif. Agric. Nat. Res. Publ. 7470. Also avail- diflubenzuron (Adept—greenhouse able online at www.ipm.ucdavis.edu use only—and Dimilin) and kinoprene REFERENCES (Enstar II—greenhouse use only) are Gill, R. J. 1982. Color-Photo and Host UC Statewide IPM Project. Dec 2000. Pest available and are applied as sprays to Keys to the Armored Scales of California. Notes: Sycamore Scale Oakland: Univ. Ca- infested plants. These materials are Scale and Whitefly Key #5. Sacra- lif. Agric. Nat. Res. Publ. 7409. Also avail- relatively slow acting but eventually mento: Calif. Dept. Food Agric. able online at www.ipm.ucdavis.edu highly effective.

For more information contact the University of California Cooperative Extension or agri- cultural commissioner’s office in your coun- ty. See your phone book for addresses and phone numbers.

CONTRIBUTORS: S. H. Dreistadt, R. J. Gill, J. G. Morse, P. A. Phillips, and R. E. Rice EDITOR: B. Ohlendorf TECHNICAL EDITOR: M. L. Flint DESIGN AND PRODUCTION: M. Brush ILLUSTRATIONS: Fig. 1: V. Winemiller; Fig. 2: D. Kidd; Fig. 3: S. Dreistadt

Produced by IPM Education and Publica- tions, UC Statewide IPM Project, University of California, Davis, CA 95616-8620

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