Root Rot – The Cancer of Our Forests

Fall 2005


Root rot, also referred to as root disease, has decimated many Inland Northwest forests. In fact, our area is considered by many to be the “root rot capital of the world.” Thankfully, there are methods to minimize the impacts of this malady.

First, let’s discuss the characteristics of root disease and how it works. As its name implies, this disease infects the roots of a tree. It is a fungus that travels between trees either by direct root contact or small fungal growths. Many tree species and brush varieties can be infected with this disease. Some are generally killed by the root rot, while others show few negative effects. Douglas fir and grand fir are highly susceptible to the disease. Western larch and pine species are generally much less susceptible.

There are many tell-tale signs of infection including thin, yellow tree crowns (needled portion of the tree), dark staining of the bark and excessive pitch near ground level. Another indication of root disease is the presence of numerous snags in the forest. One aspect of the disease that makes it so challenging is that often times two-thirds of the roots are infected before any above- ground symptoms are evident.

It should be mentioned that at least three distinct species of root disease impact trees in our local forests. Fortunately, the treatment for each of these species is very similar so it is not necessary to identify each individual species of root disease.

How do we reduce the impact of root disease? Primarily, the most successful approach is to favor the growth of tree species that are less susceptible to root disease. As previously mentioned, these species include larch, ponderosa pine, and western white pine. Favoring these species during harvest operations is highly recommended. Another approach is to create small openings during the harvest operation to allow for planting of larch and pine. These species are sun loving so the openings must be large enough to allow adequate sunlight to reach the seedlings. Many times root rot pockets are dominated by brush species. In order for the reforestation effort to be successful, this brush must be treated by mechanical or chemical means.

Hopefully, this brief overview will help you recognize and better understand root disease. Please contact our office or another professional forester for more information on this challenging forest health problem.

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