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Horticulture and Home Pest News
Horticulture & Home Pest News is filled with articles on current horticulture, plant care, pest management, and common household pests written by Iowa State University Extension specialists in the Departments of Entomology, Horticulture and Plant Pathology.

Magnolia Scale Insect

This article was published originally on 8/27/2008

 
The magnolia scale is an occasional and widely scattered pest problem in Iowa on magnolia shrubs. Over the past 20 years infestations were reported in Des Moines west of downtown (The Art Center vicinity) and Beaverdale. This summer we have heard of infestations in Des Moines, Davenport and Jefferson.
 
Magnolia scale is the largest scale insect in Iowa. Sap feeding by the scales causes stress to heavily infested plants and can result in stunted growth, yellowish discoloration of the foliage and branch dieback or death of the plant. This scale insect produces large quantities of honeydew (sugary excretion) that makes the leaves shiny, and supports the growth of sooty mold, a fungus that causes the black color. Wasps (and sometimes flies, bees and even butterflies) will visit scale-infested plants to feed on the sweet honeydew.
 
To control magnolia scales remove and destroy heavily-infested branches. Treat with a contact insecticide (horticultural oil, insecticidal soap, other ornamental synthetic insecticide) or a systemic insecticide (imidacloprid) in late August or early September. Dormant horticultural oil can also be used in late fall or early spring.
 
 
Magnolia scale.  Note the discolored foliage and sooty mold.  Photo by Jannette Thrane.Magnolia scale. Note the discolored foliage and sooty mold. Photo by Jannette Thrane.
Magnolia scale.  Note the large size.  Photo by Duane Gissel.Magnolia scale. Note the large size. Photo by Duane Gissel.

Year of Publication: 
2008
Issue: 
IC-499(16) -- August 27, 2008