Cercospora Leaf Spot of Hydrangea

Received these photos of Cercospora leaf spot on hydrangea from Gerald Roberts, county agent in Lafayette Parish.  This disease is caused by the fungus Cercospora hydrangeae, which reproduces on infected leaves that have fallen to the ground. The spores produced on these fallen leaves are either splashed onto the lower foliage or are spread by air movement.  The pathogen requires moisture on the leaves to grow and cause disease, so avoiding overhead watering is one means of reducing the chance of disease. Many of the standard fungicides available to home gardeners are also effective in controlling this disease, but they must be applied to prevent the disease from becoming established.

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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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2 Responses to Cercospora Leaf Spot of Hydrangea

  1. lynne schwartz says:

    I just bought a healthy limelight hydranga. When and how often should a fungicide be sprayed? It is hot and humid all summer in Savannah.
    Lynne

    • Don Ferrin says:

      Lynne,

      I would not begin to spray until I started to see leaf spots developing on the foliage. This disease usually starts on the lower leaves and works its way up the plant. Removing infected leaves and any that may have fallen to the ground will help to control this disease without the use of fungicides. Should you choose to use a fungicide, any of them containing chlorothalonil, myclobutanil or thiophanate-methyl should be effective. Begin spraying when you first see the disease and repeat every 10-14 days as needed.

      Donald M. Ferrin
      Associate Professor
      LSU AgCenter
      Department of Plant Pathology & Crop Physiology
      302 Life Sciences, Baton Rouge, LA 70803

      Office: 225-578-8537
      Cell: 225-573-6510
      E-mail: dferrin@agcenter.lsu.edu

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