Armillaria root rot, also known as shoestring root rot, is a soilborne disease that can affect several fruit crops, but it is most common in the eastern United States on peach and apple trees. Its host range also includes numerous species of deciduous and evergreen trees, shrubs, and woody vines. The greatest prevalence of the disease is in orchards planted on newly cleared land in which the soils are sandy and well drained. In these locations, pieces of wood invaded by the fungus serve as inoculum for infecting roots of fruit crops. Find more information in the article on Armillaria Root Rot of Apple.
Answer provided by Alan R. Biggs, West Virginia University.