Contributors: J.R. Baker, Extension Entomology Specialist; D.M. Benson, Plant Pathology,
Professor; L.F. Grand, Plant Pathology, Professor; R.K. Jones, Extension Plant Pathology
Specialist; M.A. Powell, Extension Horticulture Specialist; D.L. Stephan, Extension Entomology
Specialist; J. Scott, North Carolina Department of Agriculture; H. Singletary, North Carolina
Department of Agriculture
Crape Myrtle Diseases
POWDERY MILDEW ON CRAPE MYRTLE BUDS
Photo by P. Pritchard, North Carolina State University
Powdery mildew, caused by Erysiphe lagerstroemiae, is the
most important disease of crape myrtle. It is usually most serious in
spring and early summer and in the fall on outside plants, and it occurs
year-round on greenhouse and lath-house potted plants. It can be
especially severe in the greenhouse on plants grown for forcing. The white mycelium and spores
of the fungus coat leaves, shoots, and inflorescences, causing stunting and distortion, leaf curling,
and failure of flower buds to open properly. The entire plant may be affected. There seems to be some variation in severity on different cultivars,
especially the dwarf types. The cultivars Catawba, Cherokee, Conestoga, Potomac, Powhatan,
and Seminole were released in 1962 by the United States National Arboretum, and they are reported to be highly resistant to powdery mildew. General sanitation and good
air circulation is important in powdery mildew control on susceptible cultivars.
APHIDS AND SOOTY MOLD ON CRAPE MYRTLE
Photo courtesy of Dr. Jim Baker, North Carolina State University
Sooty mold, caused by Capnodium sp., is a dark brown or black growth of
fungus in blotches or as a complete coating on leaves and stems of plants. It results from a
non-parasitic fungus which grows on "honey dew" excretions of insects such as aphids and scale. It is a common problem on crape myrtle when the crape myrtle
aphid is not controlled.
The unsightly coating of the sooty mold fungus can be easily wiped or washed from the plant
parts. It does not damage the shrub or tree unless it coats the tree heavily. If left unchecked, this
heavy coating will interfere with the amount of light that reaches the plant. Sooty mold is
controlled by insecticide applications to
control aphids and scale insects. When the insects are controlled, no food supply is available for
the sooty mold fungus and it cannot grow.
Cercospora leaf spot, caused by Cercospora lythracearum,
is a common disease of crape myrtle from midsummer through fall in southern areas during wet
or humid conditions. The fungus causes large, dark brown, spots to develop on leaves starting at
the bottom of the plant and progressing upward. The leaves soon develop large yellow areas
around each spot and defoliation occurs. Even one or two spots will
cause a leaf to drop. In severe cases, 75 to 80 percent of leaves may be lost from a plant prior to
frost. This premature defoliation weakens the plant over a period
of years and will reduce its longevity.
Spores of the fungus are produced on the surface of diseased leaves and are spread by wind or
rain. Large numbers of spores are produced, and secondary spread to other leaves is rapid.
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Last Modified: 07/10/96