Disease Management

There are a number of common diseases in the Twin Cities that can ravage trees and landscape plants, such as apple scab, oak wilt, Dutch elm, diplodia, and powdery mildew. Our experts can identify diseases that infect trees and landscape plants, so that we can design a treatment for the specific problem.


Diplodia is a common disease of conifer trees such as spruce and pine trees. It typically infects older, larger trees. Diplodia infects the tips of the branches. Those tips turn yellow and eventually brown. Diplodia usually infects from the bottom of the tree up. In advanced stages, black dots will be present on the needles. Management of this disease is done by maintaining plant health and fungicides. All efforts should be taken to improve the plants health by managing water, fertility and other stressors. Once infected, trees are sprayed with fungicides to limit further spread of the disease.

Dutch Elm Disease

This disease has ravaged Elm Street trees throughout the Twin Cities. This leaves us with very few elm trees remaining. Dutch elm disease infects a tree’s vascular system, thus altering water movement in the tree. This is what causes elm trees to die. Wilting, yellow, or brown leaves during the season are an early symptom of Dutch elm disease. Brown streaking can also develop on branches. Fortunately, Dutch elm disease can be managed to keep your tree going for years to come. The disease is primarily managed through injection of fungicides into the tree. Insecticides are also sometimes used to manage elm bark beetles which have been known to move the disease.

Oak Wilt Disease

Oak wilt disease is a devastating disease to oak trees throughout the Twin Cities, but it can be controlled if caught early enough. The Northern Pin Oak and Northern Red Oak are the most susceptible. This disease is identified by rapid wilting. Two to six weeks after infestation the entire tree can wilt. Wilt moves from the top of the crown down the plant. Individual leaves wilt from the tips to the base. White oak trees can also get the disease, but will wilt more slowly, one branch at a time. This disease is first managed by controlling the spread of the fungus. Infected trees should be removed immediately to reduce further spread to healthy trees. Roots of nearby trees need to be disconnected by trenching into the ground. Insects can also spread the disease, so pruning should not be done in the spring or summer, but rather during the winter. If detected early enough, fungicides can be injected into the tree to stop the disease. Fungicides can also be injected to protect healthy trees. This is often done for highly critical trees.

Apple Scab

Apple scab is a very common disease on apple and crabapple trees in Minnesota. This fungus infects the leaves and the fruit of the trees, which degrades the appearance of the tree and the quality of the fruit. When infected, leaves will turn yellow and have brown spots. Often, infected trees will lose their leaves earlier in the season. When infected, a tree is more susceptible to other pests and problems. The best way to prevent apple scab is to plant resistant varieties. If you already have an apple or crabapple tree, fungicides can be used to control the disease. Multiple applications, early in the year are needed to get good control.


Powdery Mildew

Ever notice a white film on your landscape plants? That is likely powdery mildew. While this disease detracts from the plant’s appearance, it is seldom detrimental to the plant. Limit the occurrence of powdery mildew by selecting resistant varieties and avoid watering when the water will not evaporate off the leaves for a period of time. To protect valuable plants and reduce powdery mildew, plants can be treated with fungicides. Note, fungicides only work to prevent new infections of powdery mildew. Already infected areas need to be removed.

When it comes to controlling disease, whether through fungicides or management practices, you need a service that knows exactly what to do.

Contact bioTree to learn about our services and discuss your situation.


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