White pine problem
From what you describe, it sounds as though your white pines have white pine blister rust. Here is a description of this disease. Although it is from Minnesota, the material would be applicable to Vermont as well. https://extension.umn.edu/plant-diseases/white-pine-blister-rust This material describes not only identification of the disease, but also management and control. To be absolutely certain, however, you might wish to send us a specimen from the tree where the single diseased branch has now appeared. Here is a link from our website that describes how to send us a specimen: https://www.uvm.edu/sites/default/files/Extension-Master-Gardener/plantinsectworksheetforwebsite3pgs...
Good luck to you.
Dana, UVM Master Gardener Extension Help Line Volunteer