In caring for your landscape this spring, it’s important that you include an evaluation of potential tree diseases that are affecting your landscape. Below we cover four common diseases that heavily affect Minnesota.
Dutch Elm Disease (DED)
Dutch Elm Disease (DED), which first hit St. Paul in 1961, is an important tree disease to know about if you live in Minnesota. It is caused by a fungus and is transmitted by the elm bark beetle. These beetles grow and reproduce in elms, eating live and dead tissue of elms. Trees that are infected in the spring experience faster deterioration than those that get the disease later in the year. Infected trees show brown discoloration on the wood beneath the bark. This will be present before the leaves are affected. Leaves will show signs of the disease when they begin to yellow and wilt, eventually turning brown and curling.
Bur Oak Blight
Bur Oak Blight (BOB), discovered by Dr. Tom Harrington of Iowa State University, has recently been reported in Ramsey and Hennepin counties. Bur Oak Blight (BOB) is a fungus that affects an Oak’s leaves. Oak trees infected with BOB will have large, brown blemishes on the leaves, as well as brown veins. The result is an overall wilted appearance. In less common cases, there may only be small blemishes on the leaves. During the summer black blisters can form along the veins.
Oak Wilt
Oak Wilt is a caused by a fungus and is very common in Minnesota, particularly in the southeastern part of the state. Tree disease is a concern for all varieties but with the valueAlthough it can severely affect a variety of oaks, particularly red oaks, it is easier to control than Dutch Elm Disease. It is spread through root systems that are grafted, between trees that can be as far as 50 feet from each other. The leaves of red oaks will begin to brown and – you guessed it – wilt, and complete this process two to six weeks. The leaves of white oaks, although the tree is less susceptible to oak wilt, will darken as well, but also have a more evident appearance of brown around the branches (which is harder to spot on an infected red oak).
Canker
Canker comes with a variety of names, such as black rot canker or cytospora, but the symptoms are very widely the same. Typically caused by fungus or bacteria, the disease creates dead tissue on the trunks and branches of trees. As it worsens, wood decay will occur and weaken the tree. Affecting a wide range of trees including pine, oak, willow and dogwood, the canker usually starts with an infected wound and can be worsened by the tree’s environment. Although it can spread slowly, a tree with an infected trunk can die from the disease.