English names: Oak Wilt
Nordic names: Egevisnesyge (DK), Eikevisning (NO), Visnesjuka på ek (SE)
Major host plants
Quercus spp. are the only hosts of Ceratocystis fagacearum. American red oaks are very susceptible, while the white oaks Q. robur, Q. petraea, Q. suber and Q. ilex, which are important forest and plantation trees in Europe, are more resistant.
C. fagacearum causes a vascular wilt disease.
On white oaks, the wilting and death of foliage often occur only on a few branches. Quite pronounced xylem stain can usually be found in these branches. Sporulating mats are only rarely found.
On red oaks, foliage on the entire tree rapidly wilts and turns brown. Some diffuse staining may be observed in the outermost xylem ring. Within a few months after tree death, grayish sporulating mats may form below the bark. The mats have a fruity smell. The symptoms may vary depending on the Quercus species involved.
C. fagacearum is indigenous to North America and has not spread to other continents.
A map can be downloaded from EPPO's website. See instructions here.
The fungus invades the vascular system of the host and blocks xylem vessels, interfering with water and mineral uptake. This process leads to symptoms of wilting and eventual death of the tree. In a diseased white oak, distribution of the fungus is restricted to xylem of the current year’s growth. If the tree recovers, the infected ring will be buried under new xylem and spore mats are lacking. In red oak C. fagacearum produces spore mats depending on temperature. Mats are commonly found in spring and fall on trees killed by C. fagacearum the previous year. C. fagacearum spreads from diseased trees to adjacent healthy oak trees through interconnecting root systems or by beetles which serve as vectors by carrying spores from fungal mats located under the bark of infected wood. Several different beetles such as Colopterus truncatus or C. sayi (sap-feeding Nitidulidae) or, in some areas, Pseudopityophthorus minutissimus and P. pruinosus (bark beetles, Scolytidae) can act as vectors.
International spread is most likely to occur through movement of oak wood carrying sporulating mats of the fungus. If the wood carries bark, bark beetles provide a high risk for transmission. The most important means of natural dispersal is through root grafts, while spread by vectors is rare.
Detection and inspection
C. fagacearum is recognized by the presence of grayish fungal mats beneath cracks in the bark of infected red oaks. Fungal mats are not seen on white or live oaks. Conclusive diagnosis can only be made with laboratory analysis of xylem chips.
Pest status and importance
C. fagacearum constitutes a real threat to European oak species. In addition, the European bark beetle (Scolytus intricatus) appears to have the potential to be a highly effective vector.
Source of information
See further information here:
Author:Eigil de Neergaard