Q. I have had a Harry Lauder’s walking stick in my garden for over 30 years. Beyond some Japanese beetle damage, there has never been a problem. But starting a few years ago, a branch would die here and there. It is almost completely dead now. Can you tell from the attached photo what is going on?
A. Harry Lauder’s walking stick (Corylus avellana ‘Contorta’) is a cultivar of European hazelnut that is grown for its distinct contorted branches rather than nut production. It is often grown as a specimen, and its bare branches are attractive in flower arrangements. Unfortunately, European hazelnut is very susceptible to a pathogen that is native to eastern North America known as eastern filbert blight.
Our native American hazelnut (Corylus americana) is relatively resistant to this disease. It causes minor cankers but does not cause the extensive dieback seen on the European species.
European hazelnuts are valued for their nuts; American hazelnut does not produce as high a quality nut, although it is a valuable food source for wildlife. Early attempts to establish European hazelnut orchards in eastern North American failed due to this disease. While orchards were later established in the Pacific Northwest, eastern filbert blight has found its way there. Much of what we know about this disease and its management is the result of years of research at Oregon State University.
The infection starts in early spring when wind-blown spores of the fungus land on the new growth. European filberts are most susceptible as shoots are elongating and producing new leaves. This fungus is able to penetrate through the bark – it does not require a wound or natural opening. In 12-18 months, elliptical-shaped, black stromata break through the bark, usually along a branch rather than around it. Stromata are masses of fungal tissue that bear the spore-producing structures of the fungus. They will release spores the following spring, resulting in new infections on healthy branches.
Management starts with careful scouting for the stromata, and then pruning 1-3 feet below where they stop on a branch. That is followed by four fungicide applications that begin as the tree starts to leaf out and continue at two-week intervals. Oregon State has developed a spray schedule for commercial hazelnut orchards that carefully rotates among classes of fungicides to minimize the chance of the fungus developing resistance.
Harry Lauder’s walking stick at a nursery
While this management regime is great for commercial orchards, it is a challenge for ornamental plants such as Harry Lauder’s walking stick. Commercial landscape companies are unlikely to care for enough of these plants to make it worth their while to try to manage eastern filbert blight for their customers. The recommended fungicides are mostly for commercial use, which means that they come in larger containers than anyone would need for a single plant, and they tend to be expensive. Some simply are not available to home gardeners.