Disease Du Jour (August 5)

Received today’s photo of a defoliated crape myrtle from Pat Hegwood (via Allen Owings). It has been a banner year for Cercospora leaf spots, particularly on crape myrtles, although in some areas the Leyland cypress have had their share of problems, too. Typically, we don’t see as much defoliation this early as we’ve seen this year, but with the high humidity and frequent rains we’ve been getting, the conditions have been ideal for disease development. Initial symptoms on crape myrtles are the appearance of dark brown spots that develop first on the lower leaves and progress upward in the canopy from mid-summer through fall.  In many instances, infected leaves develop a yellow or red coloration due to the production of a toxin by the pathogen. These leaves then fall prematurely, particularly in highly susceptible cultivars, and serve as a source of inoculum for spread of the pathogen and further disease development. Because of this, raking and destroying the fallen leaves should be a routine practice. The use of fungicides to control this disease has not been very effective because they would have to be applied repeatedly on a regular basis throughout the growing season. Getting adequate coverage on larger crape myrtles is also problematic.

Crape myrtles defoliated by Cercospora leaf spot.

Cercospora leaf spot on crape myrtle.

 

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About Don Ferrin

I am an associate professor and extension specialist in the Department of Plant Patholgy & Crop Physiology with the LSU AgCenter in Baton Rouge. I have statewide responsibility for issues and educational programs related to diseases of all horticultural crops in Louisiana.
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