Mushroom Root Rot (Oak Root Rot) (fungi – Armillaria tabescens, Ganoderma lucidum or Armillaria mellea) attacks a wide range of orchard and shade trees as well as shrubs. First symptoms range from a slow, gradual decline to rapid death. Slow death of the tree or shrub after the affects of infection are noticed in the aboveground parts is the most common.
Dead areas are produced in the bark on the main stem and larger roots just beneath the soil surface. When the dead bark is peeled back, the white growth of the fungus over the surface of the wood constitutes a distinguishing character of this disease. The fungus occurs most frequently in woody areas or in recently cleared land. All stumps and large roots should be removed as thoroughly as possible before orchard or valuable trees are set in infested land. Planting of newly cleared land to an annual crop for several years helps to reduce this fungus.
Since the pathogen exists in most forested soils, mushroom root rot is usually related to previous stress in the tree which lowers host vigor. The stress may be environmental such as drought, flood or poor drainage; people-caused, such as construction, fill, or chemical injury; or biotic, such as severe or repeated defoliation by insects or diseases. Helping the tree to avoid stress is therefore an important part of prevention.
Lawngrass sod growing too close to a tree or shrub may encourage attack by the oak fungus. Chinaberry, rose, pyracantha, elagnus, arbovitae, and cultivated junipers have appeared especially susceptible to this disease. Peach and plum orchards are also frequently destroyed. Native yaupon and cedar are resistant. Photinia, gardenia, wax-leaf ligustrum, Japanese privet and crapemyrtle have been known to escape the disease in infected areas. Soil fumigation has not proven effective. The fungus can survive on small dead roots. Therefore, remove from the soil as many roots as possible before replanting. In addition, soil around the old root system should be fumigated or replaced with fresh soil. The objectives of these treatments are to reduce the amount of the fungus in the soil and to remove any substance that the fungus can live on.