Contorted Filbert Blight
Tom Creswell, P&PDL Director, Plant Disease Diagnostician
Contorted filbert is an ornamental cultivar of European Filbert, (Corylus avellana 'Contorta'), grown for its twisted, gnarly stems. The plant is also sold under the name Harry Lauder's Walkingstick. While it’s unique architecture can be impressive, it’s highly susceptible to a fungal canker that can cause extensive damage to the tree. Eastern Filbert Blight is caused by the fungus Anisogramma anomala and occurs in most regions where filbert is grown. Spores of the fungus are spread by wind to new trees and by splashing water to new branches within an infected tree. Dying branches signal the presence of the disease but the contorted nature of the growth may mask the distortions, swellings and cracked bark caused by the cankers. If cankers are not pruned out quickly they will continue to spread down the branches, eventually reaching the main trunk and killing the tree. This disease is difficult to control because spraying fungicides would only work if used every week throughout the growing season, making it impractical in the home landscape. Pruning to remove the cankers requires cutting several inches below any sign of discolored wood and often requires removal of so many branches that the ornamental value of the tree is lost. Infection takes place several months before the tree begins to show any symptoms so it’s easy to miss existing first year infections and the dieback may continue the following year as those young infections begin to expand and cause dieback and cankers. There are several resistant varieties of nut-bearing filberts but so far no resistant types of contorted filbert.
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Figure 1: Young contorted filbert tree showing extensive dieback
Figure 2: This branch shows swellings and bark cracks, symptoms that often point to a fungal disease.
Figure 3: The same branch with the bark peeled away shows the early stages of a fungal canker just below.
Figure 4: Swollen cankers are cut away to reveal groups of spore bearing structures shown here as individual black dots.