Armillaria root rot
Armillaria mellea (Vahl:Fr.) P. Kumm.
The bark at the crown and roots sloughs off easily, exposing the dense white growth of the fungus (A). The growth extends in a fan-like pattern underneath the bark. Black shoestring-like strands (rhizomorphs) may be obvious on the surface of the bark (B). In the fall, yellow/brown mushrooms may appear at the base of the tree, especially if killed trees are left in place (C). Trees in affected orchards will often die in a circular pattern from one or more foci in the orchard.
Occurs in all fruit-growing regions in eastern North America, but uncommon.
Any disease or disorder affecting the root system or rootstock/scion union can produce similar above-ground symptoms. The presence of rhizomorphs distinguishes this disease from similar disorders.
There are no practical control options. Stone fruit tend to be more susceptible to infection than apple and pear; however, susceptibility varies with the choice of rootstock. Of the stone fruit rootstock, Lovell, Mahaleb, Myrobalan, and Nemaguard are considered most susceptible, whereas Marianna and Mazzard are considered moderately resistant.
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