Thousand Canker Disease of Walnut - Geosmithia morbida
Symptoms / species
Impact / measures
Canopy initially pale green and sparse, later yellowish and finally brown; from August on, brown leaves are pending from dead twigs in a flag-like manner; within one season loss of leaves and drying of twigs, branches and the stem; on the surface of diseased twigs and branches small roundish bore-holes surrounded by fine sawdust; dark bark beetles, about 1mm in size (Pityophthorus juglandis. Removal of the outer bark layers reveals numerous dot-like or larger, oval shaped lesions (necroses) in the inner bark, with galleries of the beetle (=Thousand cankers). The wood remains undiscolored for a time. Death of trees usually within one year after appearance of the first symptoms.
Affected tree species
Leaf; Stem; Shoot/Twig/Branch;
Thousand Canker Disease is caused by the microfungus Geosmithia morbida. The disease has been affecting black walnuts (Juglans nigra) in the US from midth of the Nineties on, meanwhile it is widespread in North America as the most fatal disease of walnuts. It is vectored by the bark beetle Pityophthorus juglandis, which introduces the fungal spores into the living bark tissues. From the beetle galleries the fungus spreads causing the numerous necroses. The disease has been recently found in Europe (Italy), where it probably was introduced by timber from North America. There is no record of this disease from Austria up to now. Further information: Montecchio L. &
M.Faccoli 2014: First Record of Thousand Cankers Disease Geosmithia morbida and Walnut Twig Beetle Pityophthorus juglandis on Juglans nigra in Europe. Plant Disease 98,5, p.696.
EPPO: Alert List
Curative measures Thousand Canker-disease is not yet listed as the quarantaine organism in Europe (At present in EPPO Alert list). However it poses a high risk also to the indigenous European walnut (Juglans regia: for a sucessful control the disease has to be identified in an early stage. Therefore, for efficient measures (rigorose pruning of trees with low infection and removal of intensly infested trees as well as burning of the material on site!), high attention regarding any sudden decline symptoms of walnuts as well as the immediate information of the national and the regional plant protection authorities is essential.
Thousand Canker Disease, early infection stage: single branches with yellow leaves (Foto by courtesy of L.Montecchio, University of Padua)
Thousand Canker Disease, dying crown, brown leaves hanging in a flag-like manner (Foto by courtesy of L.Montecchio, University of Padua)
Thousand Canker Disease, numerous bark lesions of various size
Thousand Canker Disease, extended bark lesion
Thousand Canker Disease, twig with boring holes and sawdust
Thousand Canker Disease, vector: beetle (Pityophthorus juglandis); (Foto by courtesy of G. Fanchin, University of Padua)