Oak trees in your home garden may suddenly die if experiencing oak tree root rot. The fungal infections Armillaria root rot and phymatotrich root rot lead to the decay of your trees' root systems, leaving them incapable of absorbing water and nutrients. Fortunately, through careful maintenance and planning, you can avoid damage to your landscape and enjoy thriving, vigorous oaks.
Vigorous oak trees are more likely to avoid or have the strength to fight off fungal infections than weakened or stressed trees. Grow oak trees in locations that offer full sunlight to partial shade, advises the Clemson University Extension. Oaks generally prefer moist, well-drained soil. Avoid waterlogged soil as fungi thrive and germinate in areas that remain wet for extended durations.
Oak trees are susceptible to root rot caused by fungal infections. Fungi responsible for these infections are Armillaria that result in armillaria root rot, also called shoestring root rot. Another fungus is Phymatotrichopsis ominvorum, causing phymatotrich root rot, also called cotton root or Texas root rot. Treatment is essential as Armillaria fungi can inhabit soil for decades if left untreated, according to the University of California IPM Online.
Signs and Symptoms
Armillaria root rot causes yellow or brown leaves, leaf drop or stunted growth. Unfortunately, root rot can take hold of unseen plant parts like root systems and your oak may suddenly die without having exhibited any external symptoms. To verify that armillaria root rot is the problem, peel back a piece of bark to locate a white fungus or black-hued stringy fungal strands referred to as "shoestrings." For phymatotrich root rot look for wilted or dried brown leaves that do not fall from the branch in addition to taproots that are decaying or covered with a mold-like tan fungal growth.
Certain oak varieties, though not immune, are more tolerant or resistant to root rots. Plant these varieties when possible to avoid infection. For armillaria root rot, tolerant oak varieties include, but are not limited to, holly oaks (Quercus ilex) and valley oaks (Quercus lobata), notes the Washington State University Cooperative Extension. For phymatotrichum root rot, live oak is the only resistant variety, according to the Oklahoma Cooperative Extension Service.
For mildly infected oak trees with armillaria root rot, remove soil from rotted areas and allow it to thoroughly dry out. Remove and destroy infected plant parts and allow the roots to remain exposed through summer until soil must be replaced for winter cold protection. If your tree is only mildly infected with phymatotrichum root rot, cut back half of the top growth of the tree and keep the soil moist for approximately a month in an attempt to recover the tree's health, suggests the Oklahoma State University extension.
For severely infected plants, remove and destroy the entire tree.