Black Walnut Tree- Leaf Disease?

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Black Walnut Tree- Leaf Disease?

Question

Black Walnut Leaves Jim,

Our Black Walnut tree, planted in the desert of AZ, has developed little red and green growths growing on the leaves. They almost look like a flower bud and are soft if you break them open. See attached picture.

Will this growth hurt the tree? If yes, how do we control it?

Answer
These are insect galls formed by insects (more than likely small wasps or mites) that lay their eggs on the leaf secrete a chemical that causes the of the leaf to expand and form the gall over the egg. These are not harmful to the tree but if numerous could cause the leaves to drop early. There is no control since the life cycles of the insects and short and any treatment would need to be applied as the insects are laying their eggs--timing would be a problem and since the damage is slight no treatment is recommended.

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