Question of the Week
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Thank you to Larry for this great question! We consulted arborist Guy LeBlanc who confirmed what we thought: This is crown gall.
Guy reports, "It's usually caused by a bacterium, but some experts say other causes are possible. The source of entry is usually some kind of wound, oftentimes nematodes or other insects that invade roots. Some galls that occur low on a trunk can actually be fungal galls."
Guy also confirms that the white insects in the picture are termites. He's often seen them infest crown galls, but says that they won't harm the living portion of the tree, as our local termites just invade the dead tissue. Guy has consulted with entomologists who do not recommend treating the termites.
According to Guy, most trees he's seen with crown gall survive in very good condition without treatment. But he's also seen some that slowly decline over many years. And unfortunately, there is no successful treatment for crown gall that he knows of.
So, our advice to Larry is to keep the tree healthy, well-watered, correctly pruned, and to avoid damaging the bark.