that looks like scale and i'd treat that right away so you don't go through months of frustration. I'd go get some bondie insect control systemic pesticide. IT works great i'm just geting over scale good luck
Besides scale (which it does look like), some fungal infections show their fruiting bodies as brown nodes, too. Not sure what type of fungicide to try, but I would start with the cheapest and see if it halts the spread- some fixed copper or sulfur to start; then visit a good farm and garden store (not HD or Lowe's) where the employees are familiar with the products, and can advise you.
Regards - Nancy