NATIVE RANGE: East Asia (China, Korea, Japan)

FIRST FINDING IN SLOVENIA: 2006

PATHWAYS: transported by people with tree cutting tools. Secondary spreading by wind and insects

POSSIBLE TO FIND: year-round

DESCRIPTION: Symptoms of this diseases include brown lesions on leaves and leaf-petioles, which are the entry points of the fungi. Later, the fungus infects bark and causes lesions and dieback of shoots. Oval lesions ap-pear on the bark of the trunk, which quickly increase in size. Sometimes the tree does not die back but a canker is formed at the wound. Trees are often heavily infected and many branches die back but, at the same time, the tree also forms new shoots.

HOST PLANTS: Common ash (Fraxinus excelsior) and narrow-leaved ash (F. angustifolia) are particularly susceptible, while manna ash (F. ornus) is unaffected.

STATUS: Widespread throughout Europe.

SIMILAR SPECIES: Dieback of ash trees may also be caused by honey fungi (Armillaria spp.), which cause armillaria root disease. Weakened and dying trees are of-ten attacked by ash bark beetles, for example Leperesinus fraxini.

SOURCE: Field Guide to Invasive Alien Species in European Forests