In this article on tree diseases, Steve Nix discusses non-living agents that can act as if they were tree diseases, even though they aren't, technically. They can often look like fungi agents, for instance, until closely observed -- in other words, like the living agents that we normally associate with "tree diseases." About's Forestry Guide can tell you more about these "abiotic" tree diseases.

_{Photo ©2005 David Beaulieu (licensed to About, Inc.)}