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Martin, Engineer
Category: General
Satisfied Customers: 4776
Experience:  i'm 41 and i never stopped studying and experimenting
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What causes balls to form around the limbs of northern red

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What causes balls to form around the limbs of northern red oak trees in northern MO? Is this fatal to the tree or can the trees be saved? How is a MD going to help with my tree question???
Hello. This is usually caused by gall wasp:

Different kind of wasp can cause different "ball" configuration.

You can verify if the newer one have a larvae in them to see if it's really a wasp. This is not fatal to the tree but it can weaken it over time if there is lots of them and it then can die from oak wilt (another kind of parasite that block the vascular system).

It's kind of hard to control wasp population, the better is to let the system balance itself. An area that have lot of concentrated oak have larger chance to see a population explosion than a place with more varied tree.
Customer: replied 4 years ago.
I've read up on gall wasps & the galls or balls that we're having in the oaks are very large (4-6" diameter & up) and on both young and very mature trees. From what I've read on the gall wasps, I thought they infected the younger trees. Can all these balls be from wasps, really, that are killing the oaks around here? It doesn't seem possible.
Yep, those size are possible, even sometime bigger. One of the wasp doing those is Andricus Californicus. There is many kind of wasp and i don't think they are all discovered yet.

You should be able to see an exit hole when it's caused by a wasp (only visible when the larvae exited in adult form). Some can have hundred of hole when the wasp lay many eggs.
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