Silver leaf disease is a destructive fungal infection that targets a range of trees and shrubs, particularly those belonging to the rose family. This disease is caused by the fungus Chondrostereum purpureum, which infiltrates the wood of susceptible plants. It progresses internally, leading to a decline in tree health and, if not addressed, can ultimately result in the death of the affected parts or the entire plant.
Identifying Silver Leaf Disease
The most recognizable symptom of silver leaf disease is a distinct silver or leaden sheen that appears on the leaves of affected branches. This silvery appearance is not the fungus itself but rather a reaction within the leaf tissue. The fungus produces a toxin that causes the upper surface of the leaf to separate from the underlying tissue, creating tiny air pockets that reflect light and give the leaf its characteristic metallic luster.
A more definitive diagnostic sign of silver leaf infection is observed when an infected branch is cut open. Upon cross-sectioning, a dark, purplish-brown stain will be visible in the central wood, indicating the presence of the fungal mycelium. The bracket-shaped fruiting bodies of Chondrostereum purpureum are another indicator, though these typically appear only on wood that has already died. These purplish growths release the spores responsible for spreading the disease.
Susceptible Plants and Spread
Many woody plants are susceptible to silver leaf disease, with a strong emphasis on the Prunus genus, including plums, cherries, apricots, and laurels. Other common hosts include apples, pears, and hawthorns. The fungus spreads primarily through airborne spores, released from fruiting bodies found on dead infected wood.
Spores find entry into trees through fresh wounds on the bark. Wounds can result from pruning, accidental damage, or natural causes like broken branches. The fungus does not spread through the soil or casual contact between healthy and diseased leaves. Infection relies on direct access to the tree’s internal wood via an open wound.
Management and Prevention
There are no chemical treatments or fungicides that can cure silver leaf disease once a tree is infected. The only effective management method is removing diseased wood. When pruning, cut well below visible signs of infection, ensuring removed wood shows no purplish-brown staining.
To ensure all infected tissue is removed, cuts should extend at least 10 to 15 centimeters (approximately 4 to 6 inches) into healthy, unstained wood. Pruning susceptible trees during their active growing season, typically in the summer months, is recommended. During this period, trees heal wounds more quickly, and airborne fungal spore concentration tends to be lower, reducing infection risk.