Verticillium Wilt

This viewer thinks they have verticillium wilt in a Smoketree. Is there a way to tell before they take action? And if it is, then what happens?

Verticillium will be seen as yellowing of the foliage, followed by wilting on some branches.  It gradually progresses to more branches and will eventually kill the plant.  Once a plant is infected, there's very little you can do in terms of controlling it.  The fungus is in the soil and the vascular system of the tree. Light fertilization can mask the symptoms early on and increase the tree's vigor to it can better defend itself.  Apply a balanced fertilizer like 10-10-10, but avoid excessive fertilization.  Also keep the tree well watered, with a good soaking every two weeks. Prune out wilted branches, as the disease progresses.