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EUONYMUS SCALE

Prepared by: Steven D. Frank, Extension Entomologist

CAUTION - This information was developed for North Carolina and may not apply to other areas.
[General Information] [Biology] [Control] [Other Resources]

female scaleUnaspis euonymi (Comstock), Diaspididae, HOMOPTERA

General Information

Euonymus scale female armor is dark, oyster-shaped and 1/16 inch long. Mature males are tiny two-winged insects that emerge from their armor to mate with the females (Females do not leave the protective covering).

Eggs are tiny, yellow, oval and are only found beneath the mother's armor. Young crawlers are yellow and very small before they secrete the protective scale covering (armor).

The armor of male nymphs is narrow (1/32 in. long) and white, whereas the armor of female nymphs is dark and oyster shaped (up to 1/16 in. long). Males are usually more numerous than females, and with dense infestations, clusters of the white male armor on the leaves and twigs is noticeable from a distance.

Biology

scale encrusted stem

Euonymus scale is found throughout North Carolina wherever its host plants grow. Euonymus scale is the most commonly reported insect pest of euonymus, pachysandra and celastrus in North Carolina.  Female scale feed by inserting microscopic, thread-like mouth parts into the plant and sucking out fluids.  This results in yellow splotches on the top of leaves wherever there is a scale feeding underneath.   Leaves and stems may become encrusted with the scales to such an extent that whole branches or the entire plant may die.

This scale usually has two or three generations per year. The males emerge and mate with the females. The females lay eggs under their protective shell, and the tiny crawlers hatch and emerge from the mother's shell in April, May and June. They crawl along the leaves and stems before inserting their mouthparts.

Another brood hatches in late summer, and a partial third brood may appear even later so that all stages of development are present during most of the year. Although this scale is small, infestations are often dense and plainly visible particularly with heavy populations where males usually greatly outnumber female scales.

Management

scale infested leaf

Euonymus scale is relatively easy to scout because they make yellow blotches visible from the tops of leaves.  However, scale covers, like turtle shells, do not disappear when the insect dies. Therefore, the first thing to do is flip over female covers to determine if the scales are still alive. A live female will be an orange blob that releases juice when you smash it.  If no live scales are present, no treatment is necessary.  These will eventually weather away.

Timing is critical when trying to manage euonymus scale. The hard waxy cover protects adult scale from contact insecticides. Therefore, adults treated with a contact insecticide will live to produce another generation later that year.  Crawlers can be killed easily because they are small and unprotected by a cover. Thus, nearly all products specifically target this stage. Monitor to determine when crawlers are present.

crawlersCrawlers emerge from under adult female covers and move about the plant in April or May.  At this point the whole population is extremely vulnerable because the crawlers are exposed and all the adults from last year have died. 

Euonymus scale has 2 – 3 generations per year. Therefore, if you miss the spring emergence and crawlers are not present you will have another opportunity later in the summer.  Euonymus scale crawlers emerge about every 60 days. 

Scales are often treated with broad spectrum insecticides such as pyrethroids or organophosphates that must contact scale to kill them and also kills beneficial insects.  Horticultural oil is effective at killing crawlers on contact and has low impact on beneficial insects.  Therefore, coverage is important with these products. 

Do not spray the tender new growth of euonymus to avoid any phytotoxic effects. Spray before bud break or wait until the new growth has hardened-off somewhat. Water the plant well before spraying or spray after adequate rainfall. If the shrub is under moisture stress, the pesticide (especially oils) may damage the foliage.

Some newer products are available that offer systemic activity for longer control and are softer on beneficial insects (Table 1).  Systemic or translaminar activity allows the product to be absorbed into plant tissue.  Others can be applied as a drench to be taken up by the roots.  Thus, it reduces the need for thorough coverage on difficult to spray plant parts such as the underside of leaves. 

Another intervention option is removing problem plants.  Plants that are severely damaged from years of scale infestation or that require yearly treatment to keep scale free may not be worth the work.  Consider replacing with a newer Euonymus variety that is more resistant to scale or with another plant altogether.  Research has found Euonymus fortunei to be less susceptible to scale infestations than E. japonicas and E. kiatschovicus species.  In addition, variegated Euonymus varieties increase scale reproduction and survival more than green varieties.  The lady beetle, Chilocorus kuwanae, has been shown to be highly effective in controlling euonymus scale, but it difficult to find commercially and has been hard to locate in natural settings in NC. 


Table 1. Some of the insecticides labeled for use on armored scale in ornamental
systems that are more compatible with beneficial insects
than pyrethroid and organophosphate products.

Active ingredient

Trade name

Scale stages affected

Labeled location

Activity

Signal word

IRAC MOA group

Compatible with beneficials

acetamiprid

TriStar

Crawler, adult

G, N, L

TranslaminarSystemic

Caution

4A

Yes

dinotefuran

Safari

Crawler, adult

G, N, L, I

Systemic

Caution

4A

Yes

*horticultural oil

many

Crawler

G, N, L, I

Contact

Warning

-

Yes

*insecticidal soap

many

Crawler

G, N, L, I

Contact

Warning

-

Yes

pyriproxyfen

Distance

Crawler

G, N, L, I

TranslaminarSystemic

Caution

7C

Yes

* Suitable for homeowner use.   G=greenhouse, N=nursery, L=landscape, I=interiorscape.


Other Resources

For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service personnel.

Published by North Carolina Cooperative Extension Service Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
© 2001 NC Cooperative Extension Service
Originally Prepared by: James R. Baker, Extension Entomologist

ENT/ort-15
July 1994 (Revised) Feb. 2001 by S. Bambara.  Current revision by Steven Frank, April 2009.  

Web page last reviewed January, 2011 by webperson.