Eastern Filbert Blight on Hazelnut: Identification and Management

Eastern filbert blight (EFB), caused by the fungus Anisogramma anomala, is the most serious hazelnut disease in North America and is now a concern wherever American or hybrid hazelnut varieties are grown. It can kill susceptible plants within a few years of first infection. Understanding the disease and knowing which varieties are resistant is essential if you are growing hazelnuts where this pathogen is present.

Origin and Distribution

Anisogramma anomala is native to eastern North America, where the native American hazelnut (Corylus americana) has evolved a degree of tolerance. When European hazelnuts (Corylus avellana) or their cultivars were planted in North America, they proved highly susceptible. The disease is currently most severe in the Pacific Northwest of the United States and in commercial hazelnut-growing regions of Oregon and Washington. In Europe, it was detected in Italy and some other southern European countries and remains under phytosanitary control, though outbreaks have occurred.

Symptoms

EFB produces elongated, diamond-shaped cankers on branches and the main stem. Young cankers are sunken with a brown discolouration under the bark. As the canker expands it girdles the branch, causing wilting and dieback of the shoots beyond the canker. In late winter and spring, distinctive black stromata (fungal fruiting bodies) erupt through the bark surface of older cankers, looking like rows of raised black dots or pustules. Shoot dieback with the characteristic black fruiting bodies is the definitive sign of EFB.

How It Spreads

Spores are released from the black fruiting bodies during rainy periods in spring and spread by water splash and wind to infect new shoots. The fungus infects only very young, actively growing tissue — typically during the two to three week period when new shoots are elongating in spring. Once tissues harden, new infection does not occur. Infected plants remain infectious for years through the persistent cankers.

Management

On a susceptible variety with established infection, management options are limited. Pruning out all visible cankers — cutting well below the canker margin into clean wood — removes the source of new spores. Sterilise tools between cuts with disinfectant to avoid spreading the pathogen mechanically. In severe cases, coppicing the plant to ground level removes all infected tissue; the new regrowth will initially be disease-free but will reinfect if susceptible spores remain in the area. The most reliable long-term solution is growing EFB-resistant varieties.

Resistant Varieties

Oregon State University has bred hazelnut varieties with strong resistance to EFB, including 'Jefferson', 'Dorris', 'Yamhill', and 'Wepster'. These are the recommended choices for commercial and home growers in affected areas. European Corylus avellana varieties are generally more susceptible, though tolerance varies. If you are planting hazelnuts in a region where EFB is established, choosing a documented resistant variety is by far the most practical long-term strategy.