A Significant Root Pathogen
Ganoderma lucidum, the varnish fungus, is a pathogen that enters openings in root systems of many tree and shrub species. In our region, Red Oak, Cedar Elm, Pecan, Live Oak, Pears, and Photinia are all reported to be species commonly infected by this fungus.
The entry points can be from any activity that damages or severs a plant’s root system. Ganoderma lives in the soil as a saprophyte; that is to say, it can live on dead organic matter with no ill effects until it encounters live roots that have been cut.
Published literature suggests the fungus colonizes a plant’s root system slowly and may take several years, 10-20 has been proposed, to finally kill a tree or shrub. Some have theorized that is might just be a natural component of many old tree species. We contend it may be more aggressive than first thought. Regardless of the pathogen’s history, it causes significant damage to our shade trees by destroying a tree’s structural root system.
Trees have two primary root systems. The structural root system is responsible for anchoring a tree to the earth. A tree’s fine feeder root system is responsible for the daily demands of moisture and nutrients. Once the structural root system is compromised, a tree’s stability becomes a concern. Often, trees that fail during storms show evidence of colonization by ganoderma.
The fungus will produce a fruiting structure, a fungal conk, near the base of the tree. It is a shelf-like structure that varies in color from a rusty orange-red to a dark red with cream coloration, and is usually shiny in appearance. Once the fruiting structure is evident, the fungus has often destroyed a large part of the tree’s ability to stay anchored to the earth, thus creating a potential for failure and a potentially dangerous situation.
Above ground symptoms can mimic other problems. Trees infected with ganoderma often leaf out in the spring with significant dieback and large dead branches. Tree owners will report that the tree looked fine in the fall. Even at this stage of the infection, there may be no fungal conk apparent at the base of the tree. There is also the opposite scenario in that a tree’s canopy can look perfectly fine, but fruiting structures have developed. In either case, further investigation may be recommended. Recommendations should never include anything that is proposed to help or control the infection. Recommendations should be to immediately investigate a portion of the tree’s below ground structural root system to determine the extent of structural root loss.
The sad reality is that there is no prevention or control once a root system has been colonized. Prevention rests with the avoidance of root damage of any type, which is very unlikely in the urban environment. The positive aspect is that after investigation, immediate removal is not always necessary. Inspection of structural roots does give your Certified Arborist a baseline to make appropriate recommendations regarding a potential timeline for removal and replacement.
by Kevin Bassett and Russell N. Peters