Cause Environmental. Hazelnut bark is very susceptible to damage from full sun in summer. Newly planted trees or thick branches exposed to full sun after heavy pruning are at highest risk of damage and need protection. Wood-rotting or heart-rot fungi can colonize these areas and further weaken the tree. Young sunburned trees are also attractive to the Pacific flatheaded borer.
Application of some pesticides in the spring has been associated with increased sunburn potential of leaves in the summer. Chlorothalonil (FRAC M5) applications in the spring for eastern filbert blight management in the 1990s occasionally resulted in summer leaf sunburn. As a result some labels do not allow tank mixes with other products. Applications of elemental sulfur (FRAC M2) in spring for management of big bud mite in 2021 resulted in leaf sunburn during an extreme heat event that summer. Multiple applications of sulfur had more sunburn than single applications.
Symptoms Necrotic leaves and trunk or limb cankers on the tree's southwest side. Most severe on young trees or trees that have been pruned back severely.
- Shade southern part of trunks.
- Whitewash trunks.
- Growers have found that plastic grow sleeves are useful for newly planted trees. Use types that are opaque and do not let in sunlight. Trunks may still sunburn just above the sleeves if not shaded or painted.
- Some growers report a benefit from planting trees so they lean slightly to the southwest.
Chemical control Use before hot summer weather. Always follow pesticide label directions.
- Surround CF at 6.25 to 37.5 lb/A. A dry white film will result on all treated plant parts. 4-hr reentry. O
Reference Wiman, N.G., Webber III, J.B., Wiseman, M., and Merlet, L. 2019. Identity and pathogenicity of some fungi associated with hazelnut (Corylus avellana L.) trunk cankers in Oregon. PloS one 14(10):e0223500.