Hazelnut Branch Canker: Symptoms, Control and Pruning Methods

What Is Branch Canker?

Branch canker is a serious disease caused by the fungus Nectria galligena Bres. (current taxonomic name Neonectria ditissima), which creates chronic wounds on the trunks and branches of hazelnut trees. The disease was first described on apple and pear, and later found to cause significant damage on hazelnut as well.

Infection enters through wounds caused by frost, hail or pruning, and develops into typical canker wounds within 2-3 years. Canker wounds expand each year, encircling the branch’s vascular tissues, eventually causing the branch to dry out and die. If left untreated, the disease can significantly reduce the number of trees in an orchard.

Symptoms

Open Canker

Open cankers are the most prominent and common form of the disease. They are large wounds on the bark of trunks and branches, featuring nested elliptical callus rings with a sunken center. Each year the tree forms new callus tissue at the wound edges in an attempt to close the wound, but the fungus kills this tissue as well, creating concentric rings that resemble a target pattern.

• Size: Canker wounds can reach up to 20 cm
• Location: Trunk, main branches and base of lateral branches
• Appearance: Sunken center, raised edges, nested rings
• Bark: Cracked, dry and peeling bark tissue

Closed Canker

Closed cankers are generally observed on young branches. When the branch’s rate of callus formation temporarily exceeds the fungus’s spread rate, the wound appears to close. However, this is temporary; over time, closed cankers also develop into open cankers.

Perithecia (Spore Structures)

At the margins of canker wounds, beneath exfoliated dead bark or within bark cracks, the fungus’s reproductive structures called perithecia are visible. These structures:

• Are bright, vivid red in color
• Are spherical or pear-shaped
• Occur scattered or in clusters
• Are 1-2 mm in diameter, visible to the naked eye

Branch Dieback

When a canker wound completely encircles (girdles) a branch, water and nutrients can no longer be transported to the upper part. These branches:

• Cannot produce leaves in spring, or leaves remain pale
• Suddenly wilt and die during summer months
• Fruit and leaves turn brown but do not drop (remain hanging)

Disease Cycle

The branch canker fungus has a multi-year infection cycle. The stages of disease development are as follows:

Year 1 — Infection:

• Frost, hail or pruning wounds create entry points for the fungus
• Ascospores (sexual spores) are spread by wind and rain to open wounds
• The fungus begins developing beneath the bark, no external symptoms are visible

Year 2 — Canker Development:

• The bark at the infection site begins to sink and darken
• The first callus rings form
• Cream-white sporodochia (asexual spore structures) appear at wound margins
• Conidia (asexual spores) are spread to nearby branches by rain splash

Year 3 and Beyond — Mature Canker:

• The typical open canker wound is fully formed
• Bright red perithecia develop at wound margins
• Ascospores released from perithecia are carried long distances by wind
• The canker continues to grow each year, with growth rate highest in spring

Risk Factors

Altitude (Elevation)

There is a direct relationship between branch canker and altitude. In Turkey, the disease generally appears above 450 meters elevation, though it has been detected at 250-300 meters in some regions. As altitude increases:

• Frost events become more frequent and severe
• Frost wounds create entry points for the fungus
• Disease intensity increases in parallel with elevation

Frost and Hail Damage

Frost and hail events create micro-cracks and wounds in branch bark. These wounds are the most important entry points for the fungus to cause infection. In particular:

• Late spring frosts (April-May): Strike newly emerging branches
• Hail: Creates numerous wounds in bark, setting the stage for mass infection
• Early autumn frosts: Damage tissues that have not yet lignified

Humidity and Temperature

High humidity and rainfall are required for the fungus’s spore dispersal. Cool, humid climate conditions accelerate disease spread. For this reason, the disease is prevalent in the higher elevations of the Black Sea Region.

Susceptible Cultivars

All hazelnut cultivars can develop branch canker, but some are much more susceptible:

Cultivar	Susceptibility	Note
Fosa	Very susceptible	Planting should be avoided at high elevations
Mincane	Very susceptible	Prone to frost damage
Cakildak	Relatively resistant	Cold-hardy cultivar
Tombul	Moderate	Common in Giresun region
Palaz	Moderate	Common in Ordu region

Control Methods

There is no effective chemical treatment for branch canker. Control relies primarily on cultural measures and preventative spraying.

Control Through Pruning

Pruning of cankered branches is the most important step in disease management:

• Cut cankered branches at least 15-20 cm below the canker wound
• Remove pruning debris from the orchard and burn it — never leave them in the orchard
• Disinfect pruning tools between every cut with 10% bleach or 70% alcohol
• Prune in dry weather; pruning on rainy days increases spore dispersal
• Seal large pruning wounds with grafting wax

For detailed pruning techniques, see our Hazelnut pruning guide.

Chemical Control (Bordeaux Mixture)

While there is no effective chemical treatment, 1% Bordeaux mixture application is useful in preventing fungal entry through wound sites. The spray schedule is as follows:

1st Application — Post-harvest (late August - early September):

• Protects wounds created during harvest
• Applied immediately after pruning if pruning was performed

2nd Application — Leaf fall (November):

• Applied when 3/4 of leaves have dropped
• Prevents autumn infections

3rd Application — Spring (March):

• Applied when leaf buds begin to burst
• Provides protection against spring infections

For the complete annual spray program, see our Spray schedule.

Cultural Measures

• Cultivar selection: Choose frost-resistant cultivars for high-altitude orchards
• Orchard hygiene: Regularly collect and burn infected branches, bark and debris
• Ventilation: Reduce moisture accumulation by aerating the tree canopy through regular pruning
• Frost protection: Painting the trunk of young trees with lime wash can reduce frost cracking
• Balanced fertilization: Excessive nitrogen fertilization creates soft tissue that increases frost susceptibility

Susceptible and Resistant Cultivars

The resistance of hazelnut cultivars to branch canker is largely related to their frost resistance. Cultivars more prone to frost damage are also more susceptible to branch canker:

Cultivar	Branch Canker Susceptibility	Frost Resistance	Common Region
Fosa	High	Low	Giresun, Trabzon
Mincane	High	Low	Trabzon
Tombul	Moderate	Moderate	Giresun
Sivri	Moderate	Moderate	All regions
Palaz	Moderate	Moderate	Ordu
Cakildak	Low	High	All regions

Conclusion

Hazelnut branch canker is a long-term disease that can cause serious yield losses and tree death, especially in high-altitude orchards. Due to the disease’s 2-3 year latent development period, early diagnosis is difficult, which is why preventive measures are of great importance.

In summary:

• Regularly inspect your orchard; try to detect canker wounds early
• Prune cankered branches immediately and remove them from the orchard to burn
• Disinfect your pruning tools after every cut
• Apply 1% Bordeaux mixture after harvest, at leaf fall and in spring
• Choose frost-resistant cultivars for high-altitude orchards
• Avoid susceptible cultivars such as Fosa and Mincane

For all aspects of hazelnut care, see our Hazelnut guide. For disease and pest control, review our Spray schedule.

📚 Hazelnut Research Institute 📚 Agrowy - Hazelnut Branch Canker 📚 Agricultural Statistics 📚 TABIDER