The white “blotches” are a type of lichen. They will not harm your tree.

Keeping your fruit trees healthy and maintaining their vigor goes a long way to prevent lichens from growing on a plant. Always follow the recommended growing requirements -- watering, lighting conditions and fertilizing -- for the specific species of fruit trees. This will promote a healthy tree with a thick canopy, which reduces the possibility of lichen growth. Proper growing conditions and soil fertility can stimulate plant growth and inhibit lichens.

Copper sulfate is readily obtained online or at most garden stores, and is easiest to use in a fluid concentrate form. Although it is safe to use to treat fungus and lichen, keep children and pets away from it during application, as it can irritate skin and eyes, and can cause vomiting, and infrequently poisoning, when ingested. Wear protective clothing, and apply a watered-down solution carefully with a paintbrush (as opposed to spraying) to avoid getting it on yourself.

Lichens thrive in dark, shady, sheltered areas. If your trees are in no immediate danger and you prefer a natural route, wait for the next pruning season, and prune your trees to allow significantly more sunlight to penetrate to the trunk and branches, creating an inhospitable environment. As apples grow well in these conditions anyway, you won’t end up harming either your trees or your crop for the following season.

Hope this helps!