SNC Identification and Images

How to Identify SNC in Your Stand:  Phaeocryptopus gaeumannii & SNC symptoms

Proper identification of Phaeocryptopus gaeumannii, the fungus that causes Swiss needle cast (SNC) disease, is critical to determining whether SNC is causing the disease symptoms observed in your stand, or whether other damage agents may be to blame.

 


Identification of Phaeocryptopus gaeumannii fungal fruiting bodies (pseudothecia)

  • Pseudothecia are found on the undersides of needles and occupy needle stomates
  • Pseudothecia:
    • are brown to black and are always centered on stomates
    • have “clean” margins (not “hairy” or otherwise irregular)
    • are not significantly larger than stomates (will never overlap multiple stomates)
  • Pseudothecia of different sizes are frequently found on the same needle; large fruiting bodies are more mature than small fruiting bodies; larger pseudothecia are spherical, and begin to swell outward from stomates
  • Proper identification of Phaeocryptopus gaeumannii generally requires 10x or higher magnification with a hand lens, as other fungi may look superficially similar without sufficient magnification; 40x magnification with a binocular dissecting microscope is recommended

Photo credit: R. Mulvey

Photo credit: R. Mulvey (left), A. Martin (right)

Photo credit: R. Mulvey

Photo credit: P. Kapitola, State Phytosanitary Administration, Bugwood.org

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Symptoms of Swiss needle cast

  • Chlorosis (yellow to brown coloration) of the needles and crown
  • Premature needle loss (fewer than 3 years of needle retention)
  • Growth loss
  • Changes to wood density and other wood properties due to increased proportion latewood

Photo credit: R. L. James (left), FS 599 presentation, Oregon Department of Forestry (right)

Photo credit: D. Shaw

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NON-Swiss Needle Cast Fungi & Common Damage Agents of Douglas-fir

  • Stomiopeltis:
    large brown to black spots (large enough to overlap two or more stomates); not necessarily associated with stomates; round to oval or elongated; does not protrude from needle surface

StomiopeltisPhoto credit: R. Mulvey (Note: needles are tan due to drying and that this is not a character associated with Stomiopeltis)

  • Rasutoria:
    Large, spherical, black fruiting bodies, not necessarily associated with stomates; “hairy” margins

RasutoriaPhoto credit: R. Mulvey (Note: needles are tan due to drying and that this is not a character associated with Rasutoria)

  • Rhabdocline pseudotsugae:
    Rhabdocline needle cast; symptoms include red-brown banding and needle shed 12-15 months after infection; fungal fruiting in spring and fall; fruiting bodies are tan, and can be found under flaps in the epidermis on the underside of the needle, on either side of the midrib

Rhabdocline pseudotsugaePhoto credit: Top: J. Schwandt (USDA Forest Service) and Far Right: W. Jacobi (Colorado State University),
Bottom: P. Kapitola (State Phytosanitary Administration), J. Schwandt; Bugwood.org

  • Cooley spruce gall adelgid (Adelges cooleyi):
    Feeding on upper needles surfaces of first-year Douglas-fir needles causes yellow spots and needle kinking; insects present spring and fall; adults are covered by white, cottony wax; crawlers are small and black; damage is not usually associated with needle shed; alternate life stages for galls on spruce new growth

Cooley spruce gall adelgidPhoto credit: Left: W. Cranshaw (Colorado State University), Right: USDA FS Ogden Archive, Bugwood.org

  • Douglas-fir needle midge (Contarinia pseudotsugae):
    Feeding by small, yellow midge larvae (legless maggots) causes yellow to red spots and swelling on new growth; insects present spring to summer and cause needle shed in late summer

Douglas-fir needle midgePhoto credit: J. Schwandt, S. Tunnock, USDA Forest Service, Bugwood.org

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P. gaeumannii  vs. Other Foliar Fungi

P. gaeumannii Stomiopeltis Rasutoria Rhabdocline
Pseudothecia are brown to black, are always centered on stomates, have “clean” margins, and are not significantly larger than stomates; larger pseudothecia are spherical, and begin to swell outward from stomates; fruiting bodies are present on needles year-round, and are most abundant on older needles  Large brown to black needle spots (large enough to overlap multiple stomates); not necessarily associated with stomates; round to oval or elongated; does not protrude from stomates; grows superficially (on needle surface) and does not cause significant damage or needle shed Large black fruiting bodies (often large enough to overlap multiple stomates), often associated with stomates; “hairy” margins; protrude from stomates; only weakly parasitic and rarely cause needle senescence or shedding  Tan fruiting bodies on the undersides of needles beneath flaps in the epidermis; similar needle shed symptoms to SNC, but red brown needle banding and distinctive fruiting bodies in spring & fall

For more images of damage agents of Douglas-fir, follow these links to forestryimages.org:

Rhabdocline

Cooley spruce gall adelgid on Douglas-fir

Douglas-fir needle midge

Phaeocryptopus gaeumannii (SNC)

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A closer look at P. gaeumannii with advanced microscopic techniques

  • Cross section of a pseudothecium
  • Ascospores and germinating ascospores on water agar
  • Germinating ascospores on needle surfaces
  • Ascospore germination and penetration via stomata
  • Cross sections through stomata
  • Scanning electron micrographs of internal needle colonization
  • Pseudothecium development
  • Epiphytic hyphae 

Cross section of a pseudothecium

# Cross section of a pseudothecium
Photo credit: Stone et al. 2008, Histopathology of Phaeocryptopus gaeumannii

Ascospores and germinating ascospores on water agarPhoto credit: Stone et al. 2008, Histopathology of Phaeocryptopus gaeumannii

Germinating ascospores on needle surfaces
Photo credit: Stone et al. 2008, Histopathology of Phaeocryptopus gaeumannii

Cross sections through stomata
Photo credit: Stone et al. 2008, Histopathology of Phaeocryptopus gaeumannii

Scanning electron micrographs of internal needle colonization Photo credit: Stone et al. 2008, Histopathology of Phaeocryptopus gaeumannii

Pseudothecium developmentPhoto credit: Stone et al. 2008, Histopathology of Phaeocryptopus gaeumannii

Epiphytic hyphaePhoto credit: Stone et al. 2008, Histopathology of Phaeocryptopus gaeumannii

Epiphytic hyphae
Photo credit: Stone et al. 2008, Histopathology of Phaeocryptopus gaeumannii

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