My wife and I recently moved out of the big city and bought our first house in the country, meaning that we're now responsible for a large, beautiful, and desperately overgrown garden in the back. We're starting to learn our way around the world of plant care (the forum has been a great resource!) but we're still extremely new to this. So sorry if this is a stupid question!

While I was weeding the other day I noticed these reddish growths on the bark of our large (probably 45') willow tree. I have no idea how to ID them and haven't turned up anything conclusive on the internet. Can anyone help? I'd love to be able to save the tree if it's sick, as it's really pretty. Thanks in advance!