This doesn't appear to be a fungal disease of oak, so would not need removal or treatment, but might be a fungus growing on top of either armored scale (like Septobasidium do) or honeydew (like sooty mold). We can't see enough detail clearly to determine which is more likely. Are you able to take additional close-up pictures?

Miri

Thanks. We will get more pics. 

Melanie

Here are close up photos.

Thank you,
Melanie

Thank you for the photos. We agree with our earlier assessment that this appears to be a type of fungus called Septobasidium. These fungi do not infect trees and instead are parasitizing armored scale, a type of sap-feeding insect that lives on the bark. While the scale themselves are considered a pest, in low enough numbers they don't cause much harm to the tree and do not need control. (The fungus, in its own way, is helping to reduce the scale population by killing those it's growing over.) Since insecticides used to manage scale have the potential to impact harmless insects as well, if the tree appears to be in good health and is not declining (which may even be unrelated to a scale presence), then we do not recommend treatment.

Miri

Thanks!

Melanie

You're welcome!