I had asked about the white pine bark infection, where bark became white on several branches. Thank you for your answer. I checked the site for White pine blister rust which you suggested, and it seems that this is not the what my pine has, since the white areas do not have spindle shape. I am now resubmitting the question, since the first time a server error was reported. Thank so much for your help and support!
Thank-you for contacting Toronto Master Gardeners with your question. Unfortunately, I cannot make a definitive assessment of the problem from the attached photo of your tree. I can see a white colouration on one large branch, but I cannot see the bark clearly. The previous TMG answer wondered about a lichen on the branches. I’m not sure if you have ruled that out.
In checking on other problems of White Pine (Pinus strobus) that could have caused the whitening of the bark of the branches, I came up with a list of resources on diseases of white pine (see below). One of the main underlying problems is a general decline of white pine due to environmental stressors. Excessive heat or wetness can be issues, as can winterburn from dry, cold winds. White pine requires moist but well drained soil. These trees are also very sensitive to city conditions such as road salt.
The only condition other than white pine blister rust (WPBR) causing white patches on the branches seems to be the insect, Pine bark adelgid. According to Michegan State University’s MSU Extension on Pine bark adelgid identifying symptoms are: “Infested trees can be recognized by the presence of patches of this white, cottony material on the smooth bark of the trunks and limbs and at the bases of needles or buds. Heavily infested trees may appear whitewashed. The insect uses its long, needle-like mouthparts to pierce the tree bark and feed on the sap. Feeding is limited to the bark of the tree.” The article includes this photo of a diseased limb:
As a general reference, please have a look at the following sources on diseases of White Pine:
Finally, the other suggestion out of the first TMG answer that you might want to consider is to consult an arborist. Your tree is large and may be difficult to treat once you have determined the problem. Keep in mind that you may need to call in an arborist if your tree declines and begins to die off. It may be worthwhile to consult a professional now while you may be able to save your tree. Landscape Ontario is a good place to find a certified arborist near you Landscape Ontario
Best of luck with your tree!