See:
Cherry (Prunus spp.) - Silver Leaf
Cause Chondrostereum purpureum, a fungus that attacks shoots, branches, trunks, and roots. In Oregon, the disease has been a problem in some sour cherry and prune orchards but is also known to affect willow as well as sweet cherries, apples, apricot, pears, peaches, plums, nectarines, some small fruits (such as blueberry), alder, and poplar. The fungus is a saprophyte growing on dead trees, prunings, stumps, posts, and fallen logs. It can become an active parasite by entering living tissue through a fresh surface wound such as pruning cuts, mechanical injury, winter injury, and insect damage. Pruning cuts are most susceptible within 1 week of wounding. After infection, fungus growth is systemic.
Much of the literature about this disease on willow is about use of the fungus as a biocontrol for willow where it is not wanted in forest situations. Fresh stump cuts inoculated with the fungus results in efficient mortality of willow trees.
Symptoms A silvering of the leaves usually shows first on one or two small branches, extending rapidly to affect all branches on a limb and eventually to all limbs on the tree. The silver leaves become ashy colored, sometimes tinged with green, and edges tend to curl slightly. The leaves' light color shows a marked contrast to the normal dark green of healthy leaves. Soon after leaves silver, the branch begins to decline in vigor and dies either the same season or after one or several seasons during which leaves continue to silver.
After the branch dies, the fruiting structure of the fungus pushes its way through the dead bark and takes the shape of a bracket fungus. Brackets are quite variable in form. They appear either as flat incrustations up to several inches long covering the branches' undersides or the sides of the trunk, or as bracket-shaped projections, 1 to 3 inches wide, arranged in tiers. Bracket undersurfaces, the sporulating surfaces, usually are purple although color may vary from salmon pink to purple.
Cultural control
- Burn all prunings. The fungus will fruit only on dead wood, and pruning piles are often the source of reinfection.
- Take care to prevent unnecessary injuries to trees. Use proper branch pruning techniques.
- Prune trees in dry weather.
Reference Spiers, A. G. and Hopcroft, D. H. 1988. Factors affecting Chondrostereum purpureum infection of Salix. European journal of forest pathology, 18:257-278.