3 Chalara dieback of ash Chalara fraxinea (asexual) Anamorph of new species called: Hymenoscyphus pseudoalbidus (sexual)
4 Ash DiebackThe causal agent of dieback of European ash (Fraxinus excelsior) was first (2006) described as Chalara fraxinea.Study of the teleomorph of C. fraxinea revealed a species complex but that the strain causing ash dieback should be re-assigned to Hymenoscyphus pseudoalbidus (2011).
5 Chalara fraxinea hosts Fraxinus excelsior (European Ash)F. angustifolia (Narrow-leaved Ash)F. nigra (Black Ash)F. ornus (Manna Ash / South European Flowering Ash)F. pennsylvanica (Green Ash)F. americana (White Ash / American Ash)F. mandschurica (Manchurian Ash)
7 Impact“The disease is particularly prevalent in Denmark where up to 90 per cent of trees in many locations are infected and all are expected to die. Chalara ash dieback has the capacity to inflict on common ash what Dutch elm disease did to English elm in the 1970s. That is to essentially wipe out the species as forest, woodland, amenity and landscape tree in the UK.”(British and International Greenkeepers Association Ltd. Sept. 2012)
8 PathwaysMovement of soil, plants for planting or wood are possible pathways for long-distance transmissionWind-borne spores can move up to 30 km/yearPlants for planting from known infected areas are considered to be the likely means of entry
9 Spread from plant to plant Aerial spreadAsexual spores are not thought to be an important means of dissemination
10 Sexual sporesSexually formed spores (Hymenoscyphus psaudoalbidus) can be dispersed by wind and would appear to be the more important means of dispersal
11 Dispersal rateEvidence from Norway has suggested a potential dispersal rate of km/year.There is evidence of insect (flies; sap-feeders) dispersing other Chalara spp.
12 SymptomsSymptoms of Chalara fraxinea can be visible on leaves, shoots and branches of infected treesIn severe cases the entire crown shows leaf loss and dieback