You need to ask your yard service what they're using (weed and feed kills trees and shrubs). And who planted the trees? Did you see how they were planted and did you direct the planting party to soak the roots, untangle them from the pot and spread them in the shallow hole? And not to pile dirt too deep around the roots (you shouldn't have dirt over the root flare or the tree graft.)
Switching to an organic program, detoxing the yard, replanting the tree if necessary, and not over watering are probably the things that will help. If needed, the sick tree treatment can revive an injured or ailing tree.