03/14/2022
Rhizosphaera needle cast is a common disease on spruce trees. It is caused by fungal pathogens. For disease to occur the pathogen needs to be present, the environment needs to be conducive for disease development and there needs to be a host that is susceptible to disease.
Infection occurs in the spring usually on lower branches and works upward around the tree.
Spores spread to new needles within the tree or in neighboring trees via splashing water or wind. Current year needles will appear healthy, even though they may be infected. These needles usually turn a dappled yellow by late summer. During the late winter and early spring, the needles turn brown or purplish brown and fall off during the summer and fall. In late spring, spores are released and spread to new needles where they can initiate new infections and the cycle begins again.
Shaded trees, trees with dense foliage, and trees in areas of poor air circulation are very susceptible. Stressed trees are also more likely to suffer from Rhizosphaera needle cast.
Environmental stress, insects, and other fungal diseases can produce similar symptoms. Chemical controls are effective if the disease is not too severe. These controls are preventive in nature and applied when new needles are half elongated and again when they reach full length. Because this fungus requires twelve to eighteen months for symptoms to appear, at least two years of fungicide sprays are usually required. To reduce the risk of reinfection of older trees, continued treatments may be required.
Treating Rhizosphaera needle cast should always be done by a tree care professional. We will apply the proper fungicide designed to protect your trees from Rhizosphaera. Treatment consists of two applications per year applied when the trees are most susceptible to infection.
