Annosus Root Rot


Annosus root rot is a fungal infection that primarily attacks the coniferous trees in your home landscape, often creating complete devastation to otherwise healthy trees. This disease is indiscriminate in its attack, affecting the healthy or sick plant as well as the young or old. Due to its all-encompassing aggression, familiarizing yourself with ways to avoid infection and what to do if a problem arises will result in continued enjoyment of a healthy landscape.


Annosus root rot is caused by the fungi Heterobasidion annosum and Fomes annosus, according to the Washington State University Cooperative Extension. Fungal pathogens infect trees through two main methods of contact. One type of disease spread is caused by root contact; when a healthy tree's roots come into contact with the roots of a diseased host tree, the disease spreads into the otherwise-healthy root system. Additionally, the fungi spread sporadically, landing on trees and invading through newly cut areas or wounds.


All conifer trees are potential hosts for annosus root rot disease. However, certain species are more susceptible than others. When selecting trees for the home landscape, choose the least susceptible option for a higher chance of maintaining an uninfected tree. Some of the most susceptible species include grand firs and Western hemlocks. Trees that exhibit only moderate susceptibility include Ponderosa pines and lodgepole pines. The least susceptible of the coniferous species are Douglas-firs and spruce trees, according to the Washington State University Cooperative Extension.


Symptoms associated with the infection of annosus root rot in your conifer trees include trees that suffer from diminished health and yellowed and thinning foliage as well as malformed cones. The roots of affected trees display a red/brown color and the adherence of bark to the inner wood of the tree becomes weak. Inner wood looks speckled and covered in streaks of darker color, according to the Washington State University Cooperative Extension.


As trees decline from the fungal infection annosus root rot, they often display dark hued conks, or shelf-like fungal growths. Trees die, sometimes becoming windthrown due to interior rot. Tree stumps remaining from previously infected trees display a tell-tale sign; a conk fungal growth appear on the inside of aged stumps as well as on roots, measuring up to 10 inches in diameter with a dark top and light colored bottom, according to the Washington State University Cooperative Extension.


Trees within 50 feet of an infected tree will likely become infected, so all trees within a 50 foot radius of infected plants should be treated to establish control. Every tree within the diseased area should be cut down to a stump, according to the Washington State University Cooperative Extension. As long as stumps measure more than 18 inches in diameter, apply 1/8 inch thick layer of borax powder immediately after cutting, if possible, but no longer than after two days. Trees with smaller diameters are not a cause for concern as they rarely maintain a diseased state.

Keywords: annosus root rot, conifer root rot, annosus fungal infection

About this Author

Tarah Damask's writing career, beginning in 2003, includes experience as a fashion writer/editor for Neiman Marcus, short fiction publications in "North Texas Review," a self-published novel, band biographies, charter school curriculum, and articles for eHow. She has a love for words and is an avid observer. Damask holds a Master of Arts in English and creative writing from the University of North Texas.