Annosum root rot

Natural History
Conk growing just below the soil surface
Photo credit: G. Blakeslee - SFRC, University of Florida

Annosum root rot is a serious disease that affects trees throughout the United States but is most serious in the South and the West. Pine plantations on sandy soils in north Florida are generally high-risk areas. Annosum root rot can kill trees directly or it can weaken them and leave them more susceptible to wind damage and attack by bark beetles.

The disease is caused by a fungus (Heterobasidion annosum). This fungus produces shelflike mushrooms, called conks, that are tan to reddish brown on top and white or yellow underneath. The lower surface is covered with minute pores. Conks typically are produced at the base of the tree, often hidden from view by leaf litter. These conks produce spores that are released and carried by wind to newly cut stumps or wounds on trees. From there, the spores germinate and the fungus grows into the root system causing decay and infecting more trees as it spreads from tree to tree through root grafts and contact with other roots.


Identifying Characteristics

Identifying the disease: Infected trees tend to occur in pockets, called infection centers. The trees in the center die first. As the pathogen moves through the root systems, the spot enlarges and creates a gap in the forest. Infected trees may lose many of their needles, which turn light green to yellow. As the disease progresses, roots turn into a stringy, white mass of decayed tissue. Infected trees will often be surrounded by windthrown trees that have already lost their battle with the disease. The conks at the base of tree are usually covered by leaf litter and therefore hard to see. Conks are often absent, even on trees with advanced root disease.
Susceptible trees: Annosum root rot can affect any southern pine. Pine plantations on sandy soils with a low water table are at high risk when they are thinned and large numbers of freshly cut stumps are available for the fungus to infect.



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