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SOFT SCALE IDENTIFICATION & MANAGEMENT ON ORNAMENTAL PLANTS

Steven D. Frank, Extension Entomologist

CAUTION: This information was developed for North Carolina and may not apply to other areas.

Coccidae & Eriococcidae, HOMOPTERA

Scale insects feed on leaves or branches of many ornamental plants grown in landscapes and nurseries. They attach themselves to a plant and feed by sucking fluids through straw-like mouthparts. Scale insects can be divided into two broad categories: armored scale and soft scale. The distinction is important because behavior and management of the two groups are different. Both groups live beneath waxy covers that protect them from predators, parasitoids and pesticides. Soft scales secrete a waxy layer over themselves that cannot be separated from their body. Soft scales also excrete sugary honeydew and may move from branches to leaves during their life cycle. Black sooty mold fungus is often associated with this honeydew. In contrast, armored scales live beneath a waxy cover that is not attached to the adult body. Thus the cover can be removed to reveal the scale insect hidden below. Armored scales typically do not move once they begin to feed and do not produce honeydew.

Many soft scales have a life stage that is very dome-like or cottony so they are relatively easy to see when scouting. However, crawlers and second instars are extremely small and inconspicuous.  Soft scale damages plants by extracting plant fluids through a stylet.  This can reduce plant growth and vigor.  The most common symptom of soft scale infestation is accumulation of honeydew and sooty mold on or beneath a plant.  Other symptoms include premature leaf drop and branch dieback.  Heavy infestations can kill trees and are common on trees stressed by physical damage, drought, or improper planting. 


Common soft scale

Wax scale – There are many species of wax scale that look similar.  The most common in our area is Indian Wax scale that infests plants such as holly, barberry, cherry laurel, box wood.  Wax scale can be 3-8mm in diameter and are white, cream, pink, or gray.  Crawlers hatch around June which is the best time for control. 
indian wax scale

Fig. 1. Indian wax scale
crawlers under wax cover.

indian wax scale on maple Fig. 2. Maple tree infested with Indian wax scale.

 

Oak lecanium scale – This scale is abundant on oak and some willow species.  The most noticeable stage is a brown, convex, egg case 2-4 mm across that occurs in spring.  Crawlers emerge in late May, migrate to leaves for the summer and back to branches before fall.  There is one generation per year. 

oak lecanium scale

 

 

Fig. 3. Egg case made from dried up female oak lecanium scale on willow oak.

oak lecanium instar

 

 

Fig. 4. Oak lecanium scale 1st instar settled on willow oak leaf.

 

Cottony maple leaf scale – Characterized by white cottony ovisacs (egg sacs), this scale occurs primarily on maple but also on dogwood.  There is one generation per year. Crawlers migrate from leaves to branches where they feed and overwinter.  In early spring mature, mated females migrate to leaves for oviposition after which they die.

cottony maple leaf scale

 

 

 

Fig. 5. Cottony ovisac on maple leaf with dried, dead adult female present.

 

 

Tulip tree scale – A serious pest of tulip trees and magnolias, the 6-12mm mature females can completely encrust branches.  Females give live birth to crawlers in late summer that settle on twigs and overwinter there.  There is one generation per year.  Leaf loss, branch dieback, and tree death can result from severe infestations.

tulip tree scale

 

 

Fig. 6. Mature female tulip tree scale covering a tulip tree branch.  Honeydew is a major problem with this scale.

 

 

Soft Scale Management

Scouting for scale should be done in early spring so scale populations can be monitored for crawler activity.  Many natural enemies help suppress scale abundance and reduce damage.  If evidence of predation (scales chewed open) and parasitism (circular holes in scale covers) are present you may decide to monitor the populations rather than treat with insecticides.  When insecticide applications become necessary, dormant oil applications can be made in winter to kill scale on trunks and branches.  Otherwise target the crawler stage with horticultural oil or a systemic insecticide. 

Table 1. Insecticides labeled for use on ornamental plants to manage soft scale in greenhouses (G), nurseries (N), and landscapes (L).
*Suitable for homeowner use.

Active ingredient

Trade name

Labeled location1

Activity

 Signal word

 IRAC
MOA
group

Compatible with
beneficials

acetamiprid

TriStar

G, N, L

Translaminar Systemic

Caution

4A

Yes

buprofezin

Talus

G, N

Contact

Caution

16

Yes

dinotefuran

Safari

G, N, L, I

Systemic

Caution

4A

Yes

horticultural oil

*many

G, N, L, I

Contact

Warning

-

Yes

imidacloprid

Marathon II

G, N, I

Systemic

Caution

4A

Yes

imidacloprid

*Merit

G, N, I

Systemic

Caution

4A

Yes

insecticidal soap

*many

G, N, L, I

Contact

Warning

-

Yes

pyriproxyfen

Distance

G, N, L

Translaminar

Caution

7C

Yes

thiamethoxam

Flagship 25 WG

G, N

Translaminar Systemic

Caution

4A

Yes

 


Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data.

Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. © 2001 NC Cooperative Extension Service

For assistance, contact your county North Carolina Cooperative Extension Service agent.

Other Resources

Prepared by: Steven D. Frank, Extension Entomologist
ENT/ort-156 August, 2010 by S.D. Frank. Photos by S.D. Frank

Web page last reviewed January, 2011 by the webperson.