Dutch Elm and Oak Wilt Diseases
These diseases are caused by fungi carried by an insect from tree to tree.
Once the fungus takes hold, it grows rapidly in the water-conducting vessels of the entire tree. The vessels clog and the tree wilts and dies. The diseased tree then becomes a breeding site for more insects that will transfer the disease to healthy trees.
Dutch elm and oak wilt diseases are continuing problems within Golden Valley's urban forest. Over the past few years, the City experienced record losses to Dutch elm disease. With thousands of elm and oak trees remaining in the city, continuation of a comprehensive sanitation program is essential to keeping annual losses to a minimum.
Symptoms
The first sign of the disease is the wilting of one or more branches in the upper part of the tree. Affected elm leaves turn dull green to yellow, then curl and sometimes fall to the ground. The disease progresses down the infected branch and into the main trunk. A certified tree inspector can positively identify Dutch elm disease by obtaining a wilted branch and peeling back the bark to expose the tissue.
How the Diseases Spread
Both Dutch elm and oak wilt disease are spread two ways: overland transmission via an infected beetle and underground transmission through common root systems of like species. Elm bark beetles breed in diseased trees and in recently cut (non-diseased) firewood. They become active in April and fly from tree to tree, introducing spores of the fungus into healthy elm trees.
The picnic beetle that carries the oak wilt fungus needs an open wound (such as a pruned branch) to infect a healthy tree. Oak wilt is transmitted through root grafts or by fungal spores on the diseased tree that attract beetles This beetle is active in April, May, and June, when the tree is chemically susceptible to infection. Never prune your oaks during those months. The safest time to prune elm and oak trees is late winter, before April 1.
Firewood
Recent trimmings from elm trees, whether the tree was healthy, diseased, or died from another cause, provide excellent breeding material for the elm bark beetles that spread Dutch elm disease. These beetles breed in any dead elm wood where the bark is intact.
If you have any firewood or branches obtained from trimming or storm damage, check it for green elm wood. If you find any elm wood with the bark intact, it must be destroyed (burned), debarked, or removed by April 1. The wood cannot be safely stored in a garage or indoors.
Prevention
To decrease the chance of infection, do not trim oak and elm trees during the growing season (April 1 through September 30). Accidental wounds to oak trees during April, May, and June should be covered with pruning paint.
Disease Management Policies
Each June, July and August, the City Environmental Coordinator or Tree Inspector conducts inspections on public and private property to detect diseased elm and oak trees. If you suspect that trees on your property have problems, report them as soon as possible.
- The City is responsible for removing diseased trees from public property. Diseased tree removals on private property are the responsibility of the property owner.
- State and City regulations require you to cut down marked diseased trees and properly dispose of all portions.
- Trees must be removed within 20 days of disease confirmation and notification.
- If no action is taken by the property owner within 20 days following notice of removal, the City will issue a "Forced Removal Notice" and have the tree(s) removed. The cost of removal, plus an administrative surcharge, will be assessed against the property owner's tax liability.
- A property owner may NOT store elm wood unless all of the bark has been removed. If the stump is not removed, all above-ground portions must be debarked. These restrictions apply to all species of elm.
If you need to report a diseased tree or have any questions, call Golden Valley's Environmental Coordinator at 763-593-8046, or call the Seasonal City Tree Inspector at 763-593-3976.
