Forest Health Notes:
A Series for the Non-Industrial Private Forest Landowner

Hosts: True firs (especially grand fir) and hemlock, rarely Douglas-fir and spruce

Quick ID:

• Woody hoof-shaped conks attached to trunk under dead branch stubs
  
• Early rot: Light brown heartwood stain
  
• Late rot: yellow or rusty red stringy rot
  
• Punk knots
  
• Decay within old wounds

Field Identification

Tree & Stand: Early in the decay process, the heartwood is stained yellowish to light brown. The wood is softer in relation to uninvaded heartwood. The heartwood turns pale reddish-brown and rust-red streaks appear following the grain. Later on, a yellow or rusty red stringy rot is observed. Rotted wood may separate along annual rings. "Punk knots," or swollen knots with red interiors, may be found on the stem.

Fungus: The easiest way to diagnose this stem rot is the presence of conks on the infected tree. Conks are large (4 inches by 6-12 inches) perennial woody, hoof-shaped fruiting bodies that are black and cracked on top, grey and toothed underneath, and have a brick-red interior (the common name Indian paint fungus came from certain tribes' use of the interior for red pigment). Conks generally are formed under old branch stubs, and one large conk indicates about 20 feet of cull on either side.

May be confused with: Nothing, if conks are present.

Disease cycle: Indian paint fungus is considered to be the most serious heart rot of true firs and hemlock in Eastern Washington. Conks release airborne spores which enter new hosts through broken-off branchlets which are very small (0.1 inches). Mycelia (fungal fibers) develop within the branch stub until the stub is overgrown. Once this occurs, the fungus enters a resting state which can last for 50 years or more without causing decay. All fungi require air, moisture and a food source for development, so until air is readmitted to the interior of the trunk the disease remains dormant. Although a single tree may have several infections, most do not cause trunk decay because they either are not close enough to the trunk or do not become reactivated. Reactivation can be the result of mechanical injuries such as cat faces, frost cracks, the formation of large branch stubs, or even tiny wounds caused by fir engravers (bark beetles), all of which permit air to enter the trunk interior. The amount of decay that follows depends on the tree's age, genetic makeup, habitat type, and wound size.

Predisposing agents: This is typically a disease of overmature or mismanaged stands. Trees less than 40 years of age are not affected because of their low proportion of heartwood. Stands that are overstocked and lack vigor are more susceptible, as fast-growing, vigorous trees remain sound. Live crown ratio (percentage of trunk with a full crown, usually a function of stocking level) affects vigor and hence susceptibility. North-facing slopes have a higher incidence of decay than south-facing slopes as they are generally more moist. The species makeup of the overstory influences disease incidence for two reasons: 1) Grand fir and Douglas-fir overstories are generally more dense and moist, while pine overstories are more open and hence drier, and 2) Grand fir old
growth trees with conks can infect advanced regeneration (younger trees growing under the older trees that will be left after harvest to form the next crop). These trees are suppressed, growing very slowly as they do not receive much light. For this reason they are slow to heal small branchlet stubs, permitting a longer interval for spores to enter and cause infection. Additionally, they have more dead branchlets in their crowns which, as they are broken off, increases the total number of places the spore may enter. Later, wounding of trees through logging or other silvicultural activities can reactivate a dormant infection.

Impact: In mature and overmature grand fir stands in the Blue Mountains, expect a 50% volume loss. About one-quarter of stands sampled in eastern Washington were heavily infected, while two-thirds were lightly infected. Current management practices that favor true firs, such as overstory removal and crop replacement by advanced regeneration, may predispose stands to future volume losses.

Management: Advanced regeneration in grand fir stands should be rated for decay hazard. Some factors that may influence infection levels include: percentage of infected trees, species composition in the overstory, stand age, live crown ratio, site aspect, and percentage of trees with wounds.

It is extremely important to minimize wound damage when entering a stand to implement silvicultural treatments. As no chemical or biological method will protect a tree, wound prevention is the only effective way to keep from reactivating dormant infections. The following actions should minimize heartrot in Washington:

1. Manage susceptible species on short rotations, not longer than 150 years.
   
2. Thin trees early to increase growth and maintain stand vigor, but use care to minimize trunk wounds.
   
3. When partial cutting, select crop ("leave") trees with at least 50% live crown ratio, at least 8 inches of
   current leader growth, and the best form and height.
   
4. Minimize wounding in thinning operations, prescribed burns, slash disposal, or overstory removal. Wounds may be prevented by:
   
   • Not logging in the spring and early summer, when trees are more susceptible to injury than later in the year.
     
   • Using the proper equipment for the site.
     
   • Marking "leave" trees rather than "cut" trees.
     
   • Planning straight-line skid trails before logging, and avoid sharp turns. Leave designated "bump" trees or cull logs along the edge of skid trails.
     
   • Matching log length with final spacing. A close final spacing means skidding short logs, while longer logs are OK for wide spacing.
     
   • Logging skid trails first, before the rest of the stand, so that the skid trail is clear.
     
   • Cutting low stumps (less than 3-4") in skid trails, to keep the skidder or logs from being shunted into crop trees.
     
   • Falling trees so they are at a 45 angle directly towards or directly away from skid trails, to prevent too much maneuvering by the machinery or sharp turns by the log.
     
   • Cutting limbs flush to the bole before skidding to prevent branch stubs from shunting logs into crop trees.
     
   • Removing slash and other fuels from around the base of crop trees before underburning the stand.
     
   • Talking to anyone operating in your stand about minimizing damage to crop trees, and if necessary make contract specifications regarding penalties for damages.

Adapted from G. M. Filip et al, Strategies for reduction of decay in the interior Douglas-fir and Grand fir types, in: Silvicultural management strategies for pests of the interior Douglas-fir and Grand fir forest types, proceedings of a symposium held February 14-16, 1984; available from WSU Cooperative Extension.