Oaks are tall, majestic trees that provide visual appeal with their acorns and colorful leaves. These trees can die if they develop root rot, and the disease can spread from one oak tree to other healthy trees. Learn to recognize the symptoms and causes of root rot to keep your trees healthy or diagnose a sick tree.
Oak trees can contract many types of root rot. North Carolina State University notes the following types are present in the southeastern United States: Armillaria, Bondarzewia berkeleyi, Ganoderma lucidum, Grifola frondosa, Inonotus dryadeus and Meripilus sumstinei. In California, Armillaria and Phytophthora are the predominant types of root rot. All root rot exhibits similar symptoms, with some variety in the fungal bodies that cause the disease and the fungal growth observed on trees.
Root rot is classified as a fungal disease. Oak trees contract root rot over time, especially when they are planted in poor draining soils, since this means the roots are frequently sitting in water. Oak trees can also develop this disease if they are given too much irrigation, especially in drought-prone areas like California. Warm, humid conditions exacerbate the growth of fungi that cause different types of root rot.
Below ground, the roots of oaks can rot. They turn brown and grow mushy, and typically gardeners don't see these symptoms. Above ground, trees sometimes develop fungal bodies or growths on the trunk. These range in color from orange to cream, depending on the type of root rot. Trees also lose their leaves and grow slower. You may observe some or all of these symptoms.
You should avoid overwatering oak trees, especially in rainy periods. Plant oak only in well-draining soil so they do not develop root rot. Provide oaks annual fertilizing and pruning to keep the trees as healthy as possible, since trees under stress are more likely to develop root rot.
You can dig up the soil around the root to attempt to dry out the root system, but this does not always work. You can control the disease by applying fungicide, but cannot treat it or reverse it, as affected trees will die.