Armillaria Root Rot of Viburnum

Disease Information

Armillaria Root Rot

Symptoms and damage

Armillaria root rot is also known as shoestring root rot, mushroom root rot, and oak root rot. It is caused by the fungus Armillariamellea which is common in landscape and garden settings. This fungus can rot the roots of many different kinds of plants. Most often this disease is found on trees and shrubs such as oak, pine, rhododendron and dogwood, but hundreds of plant species, including viburnums, are susceptible. Typically the symptoms of this root rot occur over the whole plant. Above-ground parts of the shrub generally appear stunted and yellowed, and leaves may drop. The unhealthy foliage may become more sparse over a period of several years. However, there may be no evidence of any problems, and suddenly the shrub will die. The cause of the unhealthiness or death may be difficult to determine, as similar symptoms may be caused by environmental factors such as weather stress or a general lack of plant care.

Armillaria root rot can be distinguished from other root rots, or from drought or excess moisture injury, by examining the crown (lower trunk) and upper roots of the plant. If Armillaria is responsible for the plants decline, white felt-like fungal growth can be seen under the bark if the bark is carefully peeled back. If sufficient bark is removed, the leading edge of the fungal growth will be found, and this white growth has a characteristic fan-shape. The Armillaria root rot fungus also forms black, string-like fungal strands about 1/16-inch in diameter or less. These strands may often be seen between the bark and the wood, or on the surface of the roots, or in the nearby soil. These string-like fungal strands are called shoestrings, and look very similar to roots.

Management

 Provide good growing conditions for the viburnum, especially additional water during droughts, good soil drainage, and proper fertilization.

An infected shrub whose entire root system or trunk is diseased cannot be saved. When a shrub dies from Armillaria root rot, the large roots in the vicinity of the trunk as well as the trunk itself should be removed and destroyed. Soil in the immediate vicinity should also be removed. Avoid replanting the same species as the one removed.

 



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