College of Forestry
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)
- Symptoms of Swiss needle cast
- NON-Swiss needle cast fungi & common damage agents of Douglas-fir
- Table: P. gaeumannii vs. other foliar fungi
- A closer look at P. gaeumannii with advanced microscopic techniques
Identification of Phaeocryptopus gaeumannii fungal fruiting bodies (pseudothecia)
- Pseudothecia are found on the undersides of needles and occupy needle stomates
- Pseudothecia:
- 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
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
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
Photo 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
Photo 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
Photo 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
Photo 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
Photo credit: J. Schwandt, S. Tunnock, USDA Forest Service, Bugwood.org
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:
Cooley spruce gall adelgid on Douglas-fir
Phaeocryptopus gaeumannii (SNC)
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
Photo credit: Stone et al. 2008, Histopathology of Phaeocryptopus gaeumannii
Photo credit: Stone et al. 2008, Histopathology of Phaeocryptopus gaeumannii
Photo credit: Stone et al. 2008, Histopathology of Phaeocryptopus gaeumannii
Photo credit: Stone et al. 2008, Histopathology of Phaeocryptopus gaeumannii
Photo credit: Stone et al. 2008, Histopathology of Phaeocryptopus gaeumannii
Photo credit: Stone et al. 2008, Histopathology of Phaeocryptopus gaeumannii
Photo credit: Stone et al. 2008, Histopathology of Phaeocryptopus gaeumannii
Photo credit: Stone et al. 2008, Histopathology of Phaeocryptopus gaeumannii