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Black Root Rot

Xylaria mali and X. polymorpha

Black root rot, caused by Xylaria mali and X. polymorpha, is a disease of mature trees. Affected trees usually decline over a period of 3 to 4 years or more and often lean or break off just below the ground. The disease is not widespread in the Southeast, though a few orchards have experienced losses of 50% or more.

Symptoms

Above ground symptoms are similar to those caused by many root problems: trees appear weak with little terminal growth, and fruit are small. Infected roots are covered with a black fungal encrustation. The wood of infected roots is cinnamon brown, dry, brittle, and marked with brown zonations. Black fruiting structures, known as dead man's fingers, are often produced at the base of infected trees or can be found appressed to the collar. The initial source of inoculum is unknown, although several forest trees are hosts. Infection occurs when healthy roots contact infected root pieces left in the soil.

Weak tree 'Dead man's finger's'
Weak tree 'Dead man's fingers'

Control

There is no satisfactory control for black root rot. If possible, orchard sites with a history of the disease should not be replanted. If replanting is attempted, the site should be deep plowed and sub-soiled, old roots removed, and the site allowed to remain fallow as long as possible. All rootstocks are susceptible; MM.106 and seedling rootstocks are less susceptible than MM.104. MM.111 is intermediate in susceptibility. Peaches are not susceptible, and peach orchards have been successfully established in infected sites.

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Format updated March 29, 2011