Indian Paint Fungus
(Rust-red stringy rot)
Key Wildlife Value:Indian paint fungus causes decayed heartwood and hollow stems in living small-size and larger true fir and hemlock trees. Hollow stems are created during advanced stages of decay, when cylinders of rotted heartwood detach from surrounding sapwood and collapse, causing formation of a hollow chamber. Heartwood weakened by this fungus provides a substrate suitable for cavity excavation, while hollow stems provide ready-made cavities for nesting, roosting, resting, hunting, and denning. Decayed and hollow stems also provide areas of weakness where stem breakage may occur. Broken tops may provide points of entry to hollow stems, or, in conjunction with green limbs remaining near breaks, may provide structures useful for nesting or roosting. Stem breakage contributes to the formation of canopy gaps, increasing structural diversity, and adds decayed wood elements to the forest floor.
Distribution in Oregon and Washington:Commonly found east of the Cascades crest in Oregon and Washington, in the transition zone of the crest, and in southwestern Oregon; relatively uncommon west of the Cascades crest in northwestern Oregon and western Washington.
Hosts:Primarily true firs and hemlocks.
Diagnosis:Fruiting bodies are hoof-shaped, woody, and rough-textured conks, typically fist-sized or larger, with cracked, dull black upper surfaces and rough, gray to blackish lower surfaces that are comprised of closely-packed, coarse spine-like projections. The interiors of split-open conks and at their points of attachment to trees are bright orange-red to rusty-red. Conks occur most commonly in the mid-bole or lower trunk areas, attached to the trunk under branch stubs and at the locations of old, overgrown branches. Conks are perennial and persist on the bole for many years. When they get old, they eventually fall from the tree leaving rough-textured bark aberrations called “punk knots”. Sometimes the rusty-red context of the conk may still be seen in the center of a punk knot. The old conks remain on the ground at the base of the tree until they decay and, in combination with the presence of punk knots, may be used to diagnose the presence of heartrot even though no fruiting bodies remain on the bole.
Early decay appears as a light-brown stain in the heartwood that is softer than normal. Thin rusty-red or black zone lines may also be present. As the decay progresses, the soft heartwood appears to separate along annual rings, and is rust-red to brown and stringy when pulled apart. Advanced decay produces masses of long, stringy, rust-red fibers; eventually hollow stems may result.
Life History:Windborne spores infect new hosts, usually when the hosts are small and growing in the understory, through tiny (less than 2 mm) dead branchlet stubs. Slow-growing and suppressed trees are more likely to be infected than fast growing trees, because they tend to have more shade-killed branchlets and to overgrow dead branchlet stubs more slowly, providing increased opportunities for infection. Spores germinate and mycelia grow within the branchlet until it is overgrown by healthy tissue. The fungus then enters a dormant phase as a resting spore, surviving for 50 years or more until activated by a tree injury that allows air into the trunk interior near the resting spore. Wounds must be located within about 30 cm (1 ft) of the dormant infections to trigger activity. Activating wounds are commonly caused by mechanical injuries to the tree bole, frost cracks, or the breaking of a large-diameter branch close to the tree bole. Once activated, decay develops rapidly. Fruiting bodies form after extensive decay has developed and typically produce spores for several years. Conks on trees that have died or been felled may produce spores for long as 10 years after death. On average, trees with a single conk contain about 40 feet of continuous heartwood decay, with about half of the decay occurring above the conk and the other half below. Trees with many conks occurring at wide intervals up the bole are likely to be decayed for nearly their entire length.
Important Habitats and Spread Dynamics:Indian paint fungus is most common in stands that developed from dense, suppressed, true fir and hemlock understories growing under infected overstories, especially on sites where tree vigor is low. Advanced true fir and hemlock regeneration east of the Cascades crest that is more than 50 years old is likely to contain high levels of infection by Indian paint fungus. Cool, moist sites such as those found near water, on north aspects, on lower slopes, and under dense shade, as well as uneven-aged stand structures favor spread and infection by this fungus. Spores, which may be disseminated by wind over long distances, colonize tiny branchlet stubs then become dormant while host trees grow over the infections (see Life History). Activation of resting spores is favored by selective harvest activities and weather events that cause limb breakage and bole wounding.
Opportunities for Manipulation to Increase Wildlife Habitat:Retain some older true firs and hemlock (120 years old or older) in mixed stands and manage some components of pure host stands on long rotations (120 years or longer). Intentional wounding (e.g. limbing or removing large sections of bark from the bole) to activate dormant infections may be desirable in stands with no evidence of previous wounding.
Potential Adverse Effects:Decay caused by Indian paint fungus may sometimes be so prevalent in older, predominantly host species stands that undesired degradation of the existing stand structure occurs as a result of high levels of stem breakage. Riparian stands having a very high incidence of advanced rust-red stringy rot decay may not provide adequate long-term coarse woody inputs to the aquatic system, because the trees tend to shatter when they fall across the stream channel, or to float away during high-water events. On recreational sites, trees having advanced decayed caused by Indian paint fungus (indicated by a single large conk), have a high potential for failure and present a significant hazard to public safety.
How to Minimize the Risk of Adverse Effects:Managing suppressed understories that develop under infected overstories for long-term goals will maintain high levels of Indian paint fungus and associated stem breakage within a stand. A hazard rating method has been developed by Filip et al. (1983) to estimate the percentage of infection by Indian paint fungus in advanced grand fir and white fir regeneration in eastern Oregon and Washington. For situations where lower levels of decay are a management goal, this hazard rating system also provides guidelines for deciding whether to manage existing advanced regeneration for overstory replacement and for determining optimal rotation lengths. Generally speaking, it is helpful to maintain good growing conditions for understory trees that are less than 50 years old by providing adequate space for vigorous tree growth. When regenerating, employ evenage or group selection regeneration systems. Promoting non-host tree species, or a mixture of host and non-host tree species, when regenerating or thinning will help to reduce the rate of breakage in the future mature stand. Avoid excessive wounding of residual host trees in during selective harvest or other silvicultural activities, because wounding activates dormant infections. When managing true fir or hemlock in areas with a high incidence of Indian paint fungus, avoid retaining advanced regeneration older than 50 years of age, and limit harvest rotations to 150 years or less. Trees on recreational sites having conks or discernable decay exceeding prescribed levels should be topped to a safe height or removed when they are within striking distance of a target.
ReferencesAho, P.E. 1982. Indicators of cull in western conifers. USDA Forest Service, Pacific Northwest Research Station, Portland, OR, Gen. Tech. Rep. PNW-GTR-144. 17 pp.
Bull, E.L., C.G. Parks, and T.R. Torgersen. 1997. Trees and logs important to wildlife in the interior Columbia River Basin. USDA Forest Service, Pacific Northwest Research Station, Portland, OR. PNW-GTR-391. 55 pp.
Etheridge, D.E., and H.M. Craig. 1976. Factors influencing infection and initiation of decay by the Indian paint fungus (Echinodontium tinctorium) in western hemlock. Can. J. of Forest Research. 6:299-318.
Filip, G.M., P.E. Aho, and M.R. Wiitala. 1983. Indian paint fungus: a method for recognizing and reducing hazard in advanced grand and white fir regeneration in eastern Oregon and Washington. USDA Forest Service, Pacific Northwest Region, Forest Health Protection, Portland, OR, R6-FPM-293-87. 24pp.
Filip, G.M., and C.L. Schmitt. 1990. Rx for Abies: silvicultural options for diseased firs in Oregon and Washington. USDA Forest Service, Pacific Northwest Research Station, Portland, OR, GTR-PNW-252. 34pp.
Goheen, E.M., and E.A. Willhite. In prep. Field Guide to the Common Diseases and Insect Pests of Oregon and Washington conifers. USDA Forest Service, Pacific Northwest Region, Forest Health Protection.
Hansen, E.M., and K.L. Lewis, eds. 1997. Compendium of Conifer Diseases. American Phytopathological Soc. Press. 101pp.
Harvey, R.D. and P.R. Hessburg. 1992. Long-range planning for developed sites in the Pacific Northwest: the context of hazard tree management. USDA Forest Service, Pacific Northwest Region, Forest Health Protection, Portland, OR, FPM-TP039-92. 120pp.
Website linksIndian paint fungus (Rust-red stringy rot) links, An Online Catalog of Western Forest Insects and Diseases
not yet available: Field Guide to the Common Diseases and Insect Pests of Oregon and Washington Conifers