Black spots and curling leaves on Aspen & Hydrangea - Knowledgebase Question

Parker, Co
Question by pam_cohn
July 8, 2010
I sent in 2 questions last week about black spots on Aspen tree leaves (new growth) and curled leaves (new growth) on Hydrangea. I realize it was holiday, but it's been much longer than 24 hours for a reply.


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Answer from NGA
July 8, 2010

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It's difficult to diagnose a plant problem without actually seeing it so we'll have to provide only general information. Aspen leaf spot, or Marssonina leaf spot, is common on aspen trees and usually follows a spring of warm, rainy conditions which creates the perfect environment for the disease to spread.

When affected by the disease, black spots develop on aspen leaves. Symptoms occur between July and frost. Leaves affected with the disease will be scattered randomly throughout the tree and spots will appear randomly on the leaves. The spots are dark brown to black circles containing more rings, looking almost like a bulls-eye. Sometimes the edges of the spots may appear irregular or feathery.

To manage aspen leaf spot, rake fallen leaves in the autumn to prevent the spread of the fungus in the spring. Aspen leaf spot is usually not severe enough to warrant the use of fungicide, but if the symptoms occur year after year, apply a product such as Daconil 2787 in the spring when leaves are emerging from the bud. It's too late to apply fungicide once the symptoms are evident. Read and follow label directions carefully. Aspens are very sensitive to many pesticides. If applied incorrectly, pesticides can cause the leaves to turn black.

Curled leaves on Hydrangeas can be the result of a fungal disease (again from rainy spring weather), from insect feeding on the unopened bud which cause disfigured leaves, or from leaf roller insects that are currently active. Closely inspect the leaves for signs of insect activity and remove any leaves that are harboring leaf rollers. If you find no signs of insect activity, chalk the problem up to a weather related condition. You can prune away the affected leaves and your hydrangea will develop new growth and leaves that look more normal.

Best wishes with your landscape.

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