WSU Extension

Hortsense

Common Diseases : Leaf spots and blights
(revision date: 4/30/2013)


Biology
Leaf spots are localized lesions on host leaves consisting of dead and collapsed cells. Blights are general and extremely rapid browning of leaves, branches, twigs and floral organs resulting in their death. Leaf spots and blights can be caused by fungi, bacteria, viruses and environmental conditions. Many host plants are affected by leaf spots and/or blights. Determining the cause of the problem is the first step in managing a leaf spot or blight problem.
Management Options

Non-Chemical Management
  • Remove and destroy affected plant parts if an organism is the cause of the problem.
  • Protect unaffected plant tissue with appropriate fungicide applications if the problem is caused by a fungus. Application timing is critical. Read and follow label instructions.
  • Avoid wetting leaves if the leaf spot or blight is caused by a fungus or bacteria.
  • Increase plant spacing to improve air circulation and speed drying of foliage.
Select non-chemical management options as your first choice!

Chemical Management

Fungicides may be effective in managing some leaf spots and blights. Applications are made to protect plants prior to infection and generally do not cure or eradicate infections. However, the fungicide must be registered for the host plant. Contact your county extension office for additional information.

Images
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Caption: Madrone leaf spots
Photo by: R.S. Byther
Caption: Carnation fungal leaf spots
Photo by: R.S. Byther
Caption: Needle blight
Photo by: R.S. Byther
Caption: Dogwood Cylindrosporium leaf spot
Photo by: R.S. Byther
Caption: Geranium stem rot
Photo by: R.S. Byther
Caption: Pansy leaf spot
Photo by: R.S. Byther
Caption: Quince leaf spot
Photo by: R.S. Byther
Caption: Strawberry common leaf spot
Photo by: R.S. Byther
Caption: Rose Mycosphaerella leaf spots
Photo by: R.S. Byther