Plant Disease Management Handbook

Cause Several fungi have been observed fruiting from decaying commercially grown hazelnut trunks and limbs in the PNW including Ganoderma sp., a Paxillus sp., Pycnoporus cinnabarinus and Trametes versicolor (also known as turkey tail). Most fungi that cause extensive wood decay of nut trees are classified in the phylum Basidiomycota.

Cause Unknown. Witches' brooms in hazelnut are an oddity that is seen every few years. Growers are curious about the problem but do not report that it affects production in any way.

Witches' broom symptoms were associated with hazelnuts infected with Candidatus Phytoplasma fragariae in Slovenia but trees with the same pathogen in the UK only had yellowing leaf symptoms.

Cause Hazelnuts will not tolerate saturated soil conditions for extended periods of time during the winter. Trees grow poorly under these wet conditions for years and eventually may die.

See:

Hazelnut (Corylus avellana) - Wood Decay

Cause A graft-transmissible agent yet unknown. Also called stubborn, or Dilly disease, the latter for the Oregon town near which the disease was first found. Causes investigated include soilborne fungi, nematodes, and nutrition. The disease is similar to hazelnut yellows, caused by the clover yellow edge phytoplasma. The disease spreads very slowly in the field, possibly through root grafts. The cultivars Barcelona, Clackamas, and Du Chilly are the only cultivars known to be affected.

Cause Phyllactinia guttata, a fungus that overwinters on fallen leaves and fallen infected twigs. Erysiphe corylacearum has been reported on Corylus californica. The conidia are readily wind disseminated. Chasmothecia develop within the external hyphae and form appendages late in their development.

Note: Apple mosaic virus (ApMV) and Tulare apple mosaic virus (TApMv) may produce irregular yellow line patterns, whitish vein banding, or irregular yellow flecks in hazelnut leaves. Symptoms might resemble herbicide injury and spread is very slow. Many cultivars show no symptoms. The disease has not been found in commercial orchards in the Pacific Northwest but is common in Europe. Does not seem to affect tree growth or yield.

See:

Algae, Lichens, and Mosses on Plants

Cause There are a number of fungi that can cause leaf spots on hazelnut. These are of minor importance in commercial production and are more common in native hazelnuts, hedgerows and abandoned orchards. Anthracnose is caused by Piggotia coryli and leaf blister (and leaf curl) by Taphrina coryli.

Cause "Mold" is defined as any visible growth of mold either on the outside or inside of the kernel. In practice, it means any white, fuzzy mycelial growth is classified as 'mold.' Many different fungi are easily isolated from the shell or kernel, with surface sterilization, with or without any specific symptoms, before or after harvest. In Oregon, Penicillium spp., Aspergillus sp., Cladosporium sp.