Q: We have planted several trees to try to make a natural area at the rear of our property. One of the trees is a pin oak and it seems to have some kind of bug or fungus growing on it.
Can you please identify and give advice on treatment if any is needed?
A: Your trees are infested with obscure scale.
This sucking insect can severely weaken the plants it attaches to. My guess is that it came in with the trees you bought.
For now, spray each tree thoroughly with horticultural oil in March and again in four weeks
Do again next spring.
see Obscure Scale