This week's topic is of a rather delicate nature but nevertheless must be dealt with as promised in a previous HHPN article. Does your tree suffer from butt rot? Don't be embarrassed if you can't answer because this disease often takes place under our noses for years without our knowledge. It may eventually manifest itself in the form of shelf or bracket fruiting bodies or mushrooms. We may consider these fruiting bodies at the base of the tree or on the ground under the canopy of the tree as fair warning that a considerable amount of rot has already taken place in the roots or in the wood at the base of the tree. It tells us that the support structures that are holding the tree up are no longer sound. Since this increases the likelihood that it will fall with a strong wind, removal may be necessary to prevent the tree from damaging people or property. On the other hand, a tree with either condition may unceremoniously keel over or snap off in a wind storm without any warning at all.
So how does this condition begin? As in heartwood rot discussed previously, a butt rot or root rot pathogen can invade a susceptible tree through wounds. Unlike heartwood rot, however, root rot and butt rot can also be transmitted through naturally grafted roots from infected trees, or even dead trees. If invasion and subsequent rotting occurs in the wood at the base of the tree, it is called "butt rot." If it occurs in the roots, it is called "root rot." Both rots may be caused by the same fungus, and a number of different species can attack tree roots and butts. Wounds to the tree base can be caused by lawnmowers, wayward automobiles, heavy equipment, etc. Roots can be wounded by trenching equipment when work on gas or water lines is being done; by digging into the root zone while building driveways, sidewalks, roads, etc.
Symptoms may include die back of branches in the canopy, and fewer and smaller than normal leaves, but these are symptoms of other problems as well. The sure sign of butt rot is the production of fruiting bodies such as hen of the woods (Grifola frondosa), honey mushroom (Armillaria mellea), or artist's conk (Ganoderma applanatum) near the base of the tree. A common root rot fungus in the Midwest is Laetiporus cincinnatus, an apricot colored sulfur shelf with white pores that appears on the ground, but is actually growing from infected roots.
Unfortunately, there is nothing that can be done to cure a tree once root rot or butt rot is discovered. Prevention is the best way to avoid these diseases. Put mulch around the base of trees both to prevent accidents with the lawnmower and to keep down competition with other plants such as grass; work with your contractors to make sure that they understand the importance of avoiding injury to your tree trunks or roots; keep your trees healthy by watering them deeply during drought; and avoid stresses such as compaction and soil overtopping under the canopy.
A healthy tree has the tools and energy necessary to keep its roots and butt safe from fungal invaders, and keeps the homeowner safe from embarrassing questions.
Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on July 11, 2007. The information contained within may not be the most current and accurate depending on when it is accessed.