Diamond willow

Diamond willow
A stick of diamond willow.
Causal agents	Valsa sordida
Hosts	willow trees
EPPO code	VALSSO

Diamond willow is willow with wood that is deformed into diamond-shaped segments with alternating colors. This is most likely the result of attack by a fungus (Valsa sordida and possibly others), which causes cankers to form in the wood in response to the infection. Diamond willow is prized by wood carvers and furniture makers for its strong contrasting colors (red and white) and its sculptural irregularity of shape.

There are at least six different species that have been identified as being susceptible to diamonding, including Salix bebbiana, the most common diamond willow, plus S. pseudomonticola, S. arbusculoides, S. discolor, S. scouleriana, and S. alaxensis.

The diamonding is usually found with a branch at its center or is found in the Y of a tree. Diamonding in willow does not seem to be specific to an area that willows grow in, and where one bunch of willow will have diamonds, the next clump of willows may have none at all. Although diamond willow is often thought of as being a northern phenomenon, of the boreal forest, there is mention of diamond willow growing as far south as Missouri.

The tree grows diamond-shaped cankers in response to the fungus. The cankers seem to result from the tree growing away from the site of attack. This usually happens at the crotch of a branch on a larger branch or main stem. If the branch is relatively small it seems to die very quickly. If the branch is larger, it may continue to grow and the diamond is formed on the branch and the stem. By growing away from the fungus, new layers of growth occur further and further away from the site of the fungal attack. Thus the affected area gets larger and deeper. If the tree has been affected in several places close together, then the diamonds run into each other. This can result in pronounced ridges if some sapwood continues to survive, or it may strangle the small ridge of sapwood, which then dies.