Corylus avellana · Shrub
Powdery mildew: Improve air circulation by thinning the canopy and apply a fungicide if infection is severe.
Honey fungus: Remove infected roots and replace soil, as there is no chemical cure for established infection.
Silver leaf: Prune out affected branches well below the visible symptoms and burn them immediately.
Aphids: Encourage natural predators like ladybirds or use a strong jet of water to dislodge them.
Gall mites: Prune out severely affected growth in winter to reduce populations before they spread.