Hi Mary, thanks for using Ask Extension 

The white fuzzy material you’re seeing on the trunks is consistent with pine bark adelgid (sometimes referred to as wooly aphids) a small conifer‑feeding insect that produces a white, cottony wax on bark surfaces. A trunk wash can remove the visible white buildup, but it is not required for tree health. On mature white pines (like your ~30‑year‑old trees), pine bark adelgid feeding is generally cosmetic and does not harm the tree.

If you prefer treatment for appearance, a horticultural oil trunk wash is acceptable, but it should be applied under the right weather conditions and only when the trees are not drought‑stressed.

You do not need to treat the rest of the trees on your property. Adelgid populations are usually patchy, and even when present, they rarely require whole‑property management. Monitoring is sufficient. 

Check out the following links:

Pine bark adelgid becoming active in white pines - Christmas Trees

Pine Bark Adelgid | Yard and Garden

I hope this is helpful.