Laminate Root Rot

Asked August 25, 2020, 4:45 PM EDT

I have FS permit cabin on the Upper Rogue River at Union Creek in Jackson County. We had a hemlock go down this past winter. Its roots were like paper and there was signs of rot in the trunk. My question is about neighboring tree? What is the chances of other trees being hazard trees? Thanks inadvance. Brad Cummings, RPh OSU Pharmacy 1987.

Jackson County Oregon

1 Response

C. sulphurascens is nearly ubiquitous throughout most Douglas-fir and grand fir forests in Oregon and Washington. It is particularly prevalent, commonly causing large infection centers, west of the Cascade Mountains and on the Cascades crest. In drier eastside types, laminated root rot is commonly found on north-facing slopes and stream bottoms, although it may also occur in other locations. Very large, circular infection centers (up to 40 ha, or 100 ac) are found in mountain hemlock stands in the high Cascade Mountains of central Oregon. This fungus depends for its survival upon the connected roots of live host trees and the dead underground portions of infested roots and stumps, especially large ones. It does not appear to be restricted by climatic or site conditions, or influenced by tree vigor-enhancing treatments such as thinning or fertilization. Continuous cover of highly susceptible species provides favorable habitat for C. sulphurascens, especially when large infected stumps are also present. Laminated root rot usually intensifies when infection centers and adjacent areas are regenerated with highly susceptible species.

Laminated root rot spreads primarily through root-to-root contact between infected and uninfected host trees. It does not spread through uncolonized dead wood, but may infect a live root that grows into contact with infected dead wood. It successfully infects host trees regardless of their vigor. There appears to be no reliable method of long-distance spread. Crown symptoms may appear within 5 to 15 years following initial infection, and larger trees live an average of 10 years after the onset of crown symptoms. Seedlings planted into inoculum may die within the first year. Colonized stumps and infected trees serve as “centers” of gradually expanding root disease infection areas as the fungus slowly moves down colonized tree roots and up the roots of previously uninfected individuals. Infection centers expand at a rate of about 30 cm (12 in) per year. The distribution of infection centers may be diffuse, with diseased individuals or small groups of 2 to 3 trees occurring scattered throughout the area of infection, or discrete, with discernable margins marking the transition from aggregations of diseased trees to healthy forest.

The ability of laminated root rot to survive in a location and to spread is influenced by the abundance, density and spatial arrangement of susceptible host species, the size of infected trees and stumps, and the amount of time since the site was occupied by living susceptible hosts. Because laminated root rot is able to persist on a site for very long periods, it may be considered a permanent resident unless suppressive management actions are undertaken to ensure either the removal of inoculum or the absence of host trees for at least 50 years.

Several management approaches are available for minimizing the adverse effects of laminated root rot. The most opportune time to apply most strategies occurs during final harvest and stand regeneration activities, although, depending the strategy selected, helpful actions also may be undertaken at other times.

One approach involves favoring less susceptible and immune species on sites infected with laminated root rot. This approach does not eliminate the pathogen from the site because the fungus continues to survive on the less susceptible species, but reduces the effects of disease upon the stand. This approach is usually preferred on heavily infested sites, because it is generally cost effective, and maintains conifer cover on the site. Less susceptible and immune species may be planted when a stand is regenerated, or they may be favored during intermediate entries such as thinning and partial cutting.

A second approach is to create a buffer between an expanding laminated root rot infection center and the adjacent portion of the stand that is judged to be healthy. This may be accomplished in several ways, from complete removal of trees for a prescribed distance, usually 15 m, surrounding the center, to removing only host trees from the buffer area. This approach requires accurate information on the spatial distribution of the root disease in the stand, obtained by conducting a root disease survey, before implementation is considered, and is appropriate only in situations where distribution of the fungus is discreet and not diffuse. To be effective, host trees that seed in following initial treatment should be periodically removed from the buffer area during subsequent management activities, e.g., precommercial thinning.

A third approach is to attempt to eliminate the pathogen from the site. This may be accomplished either preventing the growth of host tree species until the pathogen has died out or by removing inoculum from the site. The first strategy, preventing the growth of host tree species until the pathogen dies, limits site occupancy to immune species, such as various hardwoods, for a period of 50 years or more. West of the Cascades crest, red alder, which has been hypothesized to function as a natural biological control of laminated root rot, has most commonly been used in this capacity, because it can quickly occupy the site after being planted, effectively preventing susceptible conifer species from growing, while also providing commercial products. A possible disadvantage to this strategy, depending on management objectives, is the long period of time that conifers must be excluded from the site in order for the strategy to be effective. Periodic entries to remove host species ingrowth may be required to maintain effectiveness. The other strategy, inoculum removal (stump and root removal) has been shown to be effective, but is expensive and involves intense use of heavy equipment, which carries a risk of significant negative effects upon the soil and subsequent tree growth.

On recreational and administrative sites, forest work sites, and along prioritized roadsides, infected trees within striking distance of a target should be removed or topped to a safe height, or the situation arranged so that people are not exposed to danger.

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