Diseases of the Fremont Cottonwood Tree

Armillaria Root Rot

• Armillaria root rot, or the oak root fungus, is cited as a potential disease of Fremont cottonwood by the University of California Extension. The disease is a root malady caused by Armillaria mellea and leads to extensive root and trunk damage. Early symptoms include discoloration, stunted leaf growth and premature leaf drop. The branches start to die gradually, usually around the top of the tree first. Eventually the entire tree dies. There is often the growth of mushrooms at the tree base. No cure for armillaria root fungus exists. The best management is to plant resistant species and the avoid planting in areas with prior cases of Armillaria.

Bacterial Blight

• Bacterial blight is a potential disease of the Fremont cottonwood tree, according to the University of California Extension. The disease is caused by Pseudomonas syringae and is characterized by the appearance of small, black or large brown spots on the tree foliage, followed by blossom and branch tip dieback. The veins of the foliage blacken and stem cankers form. The disease is more prevalent during wet weather. Management includes pruning the infected tree areas during dry weather to minimize the spread of the disease. In cases of severe infection, cankers appear on the trunk. Remove severely infected trees entirely.

Wetwood

• Wetwood, also referred to as Slime flux, is a bacterial disease of Fremont cottonwood, as cited by the University of California Extension. The disease appears as stained, wet looking areas on the trunk and branches accompanied with secretion of tree fluids. Wetwood is more common on trees that are 10 years or older. As the disease progresses, the foliage starts to wilt and branch dieback occurs. Management includes avoiding unnecessary injury to trees, as this creates bacterial entry points. Open the smaller wet area and expose it to air to keep liquid from accumulating.