Annulohypoxylon canker, or Hypoxylon canker—Annulohypoxylon (=Hypoxylon) spp.
These fungi are secondary pathogens that can become opportunistic and cause disease when the host is severely stressed. For example, after tanoak and true oaks become diseased from Phytophthora ramorum, the cause of sudden oak death, Annulohypoxylon thouarsianum commonly causes sapwood decay that hastens tree death and increases the potential for limb and trunk failure.
Identification
Annulohypoxylon spp. produce hard, black to dark brown spore-forming bodies (stromata), sometimes in great numbers, on the surface of infected bark and wood. With A. thouarsianum, these fruiting bodies are black, hemispherical, and often about 1 inch in diameter.
Life cycle
Annulohypoxylon spp. can infect hosts without causing obvious symptoms of disease or infection. When hosts become damaged from other pests or injuries, Annulohypoxylon rapidly develops and causes white rot in sapwood.
Immature stromata emerge through the bark over wood infected by Annulohypoxylon. Stromata initially are covered with a dark, smooth, glossy membrane. The short-lived membrane ruptures, revealing powdery, dark olive green asexual spores (conidia) on the surface of the stroma.
Sexual spores (ascospores) form in a single layer of flask-shaped structures (perithecia) just below the surface of the stroma. Fine bumps covering the stroma surface are the rounded openings of the perithecia, from which ascospores are released.
Solutions
Avoid disease by planting species that are well adapted for conditions at that location. Protect plants from injury, stress, and other pests and provide proper cultural care, especially appropriate irrigation.
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Annulohypoxylon spore-forming bodies
Stromata on a dying coast live oak
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