I had never experienced eastern filbert blight (Anisogramma anomola) until this year, and my first exposure was a rude awakening. Last year my glorious contorted filbert (Corylus avellana var. contorta) was a prime specimen. By late summer, strange patterned cankers appeared on some of the branches accompanied by dieback. By this spring, new leaves barely appeared and the death of my beloved shrub was nearly complete. Never have I seen a disease consume a large, woody plant so completely and with such speed.
Here's the story. This North American fungal blight attacks the native hazelnut or filbert (Corylus americana) but native species are resistant and don't die. Some stem dieback will occur with natives, but diseased branches are easily pruned away. Non-native hazelnuts have a different fate.
European hazelnuts (Corylus avellana), Turkish hazelnuts (Corylus colurna), giant filberts (Corylus maxima) and other Old World species are quickly taken by the disease with no chance of survival. For this reason, hazelnuts are not grown as a crop in the Northeast US.
Once stems show the telltale signs of disease, there is no need to try to save your ornamental filbert. It must be replaced with something else.