Fruit IPM Fact Sheet
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Forbes Scale

Scienctific Name--Quadraspidiotus

Reference: Common Tree Fruit Pests, NCR 63,
Angus Howitt, 1993
Michigan State University

This pest has been known in the Midwest since 1894.  Originally, it was thought to be primarily a pest of cherry.

Life Stages
Egg: The female gives birth to living young.
Crawler: These are small and lice-like, with six legs and one pair of antennae.
Adult: The adults are similar to San Jose scale, except that Forbes scales have a raised, reddish area in the center and San Jose scales have a pale yellow nipple in the center.

Host Range
Forbes scale is found anywhere east of the Rocky Mountains on apple, cherry, apricot, pear, plum and currant.

Injury or Damage
Like the San Jose scale, the Forbes scale feeds on the sap of the tree, weakening and eventually maybe killing the tree.

Factors Affecting Abundance
Predators and parasites are important factors in the control of this pest.  Mild winters favor the Forbes scale, while severe winters cause high mortalities.

Life History
The scales pass winter partly grown.  The males emerge in the spring and make with the females.   The nymphs appear in May and June, being produced oviparously and ovoviviparously.  In the north central states, one generation occurs per year.

Monitoring
This pest is much less prevalent than the San Jose scale.   To distinguish between the Forbes and San Jose scales, examine the nipples of the insects.  The San Jose scale has a pale yellow nipple, while that of the Forbes scale will appear as a raised, reddish area in the insect’s center.  In the late crawler stages, this pest is similar to the San Jose scale but is a little larger.  It is also brown, compared with the San Jose scale’s dull black.

Control
Summer applications of chemicals will control this pest.

*Data from JSU PETE model.

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created: October 13, 1998
Last modified: October 19, 2009