Unusual growth in oak leaf - Ask Extension
One of our oaks has these white unusual formations or tumors in its new leaves. Most of the new leaves have this, and we found no trace of an insect o...
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Unusual growth in oak leaf #309312
Asked March 26, 2016, 3:44 PM EDT
One of our oaks has these white unusual formations or tumors in its new leaves. Most of the new leaves have this, and we found no trace of an insect or aracnid. Could you tell us what it is and how to fix our tree? Thanks.
County Outside United States
Expert Response
Good Morning,
These are likely cynipid wasp or midge galls. They are structures created by the mother insect inserting her eggs into the buds or very young leaf tissues. Usually, there are some fluids that mimic plant hormones and perhaps some viruses as well that hijack the tree's systems and cause it to create these structures for the larval insects to grow in.
Unless the tree is being defoliated repeatedly by these galls (they'll drop off in a month or so) it is unlikely the tree is suffering much. I suggest a wait and see approach.
There are treatments you can use, depending on tree size, if the galling becomes extreme and the tree begins to suffer. These treatments are themselves a bit hard on the tree or the general environment around it. Drenches with neonicotinid insecticides to be taken up by roots in the fall, trunk injections (very invasive), or foliar sprays (if the tree is small enough).
These are likely cynipid wasp or midge galls. They are structures created by the mother insect inserting her eggs into the buds or very young leaf tissues. Usually, there are some fluids that mimic plant hormones and perhaps some viruses as well that hijack the tree's systems and cause it to create these structures for the larval insects to grow in.
Unless the tree is being defoliated repeatedly by these galls (they'll drop off in a month or so) it is unlikely the tree is suffering much. I suggest a wait and see approach.
There are treatments you can use, depending on tree size, if the galling becomes extreme and the tree begins to suffer. These treatments are themselves a bit hard on the tree or the general environment around it. Drenches with neonicotinid insecticides to be taken up by roots in the fall, trunk injections (very invasive), or foliar sprays (if the tree is small enough).
