Around the Seattle area this spring I noticed a number of Japanese Maples infected with what appears to be verticillium wilt (Verticillium dahliae and V. albo-atrum). This soil borne fungi can infect a very wide range of species. It causes withering, wilting, yellowing of foliage, and decline or death in woody and herbaceous plants around the world in temperate climates. The species I most often see affected are Japanese Maples, although it infects a very wide range of woody species .
While some plants and trees can fight off an infection for years by putting on new wood over the infected wood, when trees are put under stress is often when symptoms begin to show. Transplanting seems to make trees particularly vulnerable. A water stressed plant is also much more likely to become overwhelmed by the wilt. This is another reason to transplant in the cool season and keep your trees well watered through the dry season their first couple of years.
Trees that become infected while in nurseries often develop symptoms during the first one to two years after transplanting, but later enter long term remission. So don’t necessarily give up on a tree because it looses a few branches.
The reproductive structures of verticillium wilt remain in the soil for years, making it nearly impossible to control once an area shows signs of hosting this fungus. If a number of the trees in an area are dying from this, it may be best to replace them with a resistant species. A number of interesting and ornamental trees are known to be resistant, such as ceanothus, dogwood, apple and crabapple, honeylocust, and pawpaw, to name just a few.
Sources: Diseases of Trees and Shrubs 2nd edition W.A. Sinclair & H.H. Lyon. pgs. 242-245.