Blisters on oak leaves - Knowledgebase Question

Deerfield, Il
Question by JFiremanMD
July 11, 2010
I get yellow blisters on the leaves of my oak tree in the spring and summer. What are they, and do I need to treat it?


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Answer from NGA
July 11, 2010

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The blisters are called galls and are the result of mites, midges or tiny wasps either feeding or laying eggs on the leaves. The galls form because of a chemical released by the insect. Although the galls are odd looking they don't really cause any damage to the tree and they are cyclic. Some years you'll see more damage than other years. It's difficult to control the insects because they fly around but if you don't like the galls you can use a systemic as a soil drench. It won't change the leaves this year but by next spring the insecticide will have traveled throughout the tree and will kill any insects that try feeding or puncturing the leaves to lay their eggs. I just leave them alone. The galls are interesting and the insects, especially the wasps are beneficial in the landscape.

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