Disease Problems - Cercospora Leaf Spot

   

SYMPTOMS

Circular to angular brown spots begin occurring on the older, lower leaves in late June and July. The leaves begin to turn bright yellow, orange or red and fall from the tree. As the summer progresses, many infected trees will have dropped all but the newest leaves. Repeated infections year after year will severely stress a tree and reduce its longevity.


DESCRIPTION OF PEST

This fungus colonizes leaf tissue and causes distinct sunken brown spots on leaves. Within the spots, there may be black fruiting structures evident with magnification.
 

spots and yellowed leaves

Small distinct spots and yellowed leaves
may be evident in early summe

LIFE CYCLE

Spores are produced within tiny stromata which erupt through the leaf surface. These spores can be splashed from leaf to leaf causing new infections during warm, wet weather.

sunken angular lesions

A closer view showing the sunken,
angular lesions

MANAGEMENT

CHEMICAL
Fungicides can be utilized to control Cercospora leaf spot on susceptible crapemyrtle varieties. This should be started in early summer when the spots are first noticed and continued at one to two week intervals when the weather is warm and wet. Consult your local Extension office for fungicide recommendations.

BIOLOGICAL
The best biological control is selecting a planting site with good air circulation so that the foliage will dry quickly. Thinning interior branches will also promote air flow. The varieties Apalachee, Caddo, Catawba, Sioux, Tonto, Tuscarora, Tuskegee, and Yuma have been shown to have resistance to this disease.

leaves have dropped

By late summer all but the newest leaves
have dropped from this tree.

stromata

A magnified view of the lesion shows the
small, black fruiting structures (stromata) which contain masses of spores.
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