Dutch Elm and Oak Wilt

Dutch elm disease and oak wilt are infectious tree diseases controlled annually under the provisions of City Ordinance 1055.

A designated tree inspector hired by the City of Edina and certified by the State of Minnesota has the lawful right to enter upon private property for the purpose of inspecting for and controlling the spread of Dutch elm disease and oak wilt.

Although the biological make-up of these two diseases varies, the removal of infected trees is a necessary and proven method of minimizing the spread of both. While removal alone will not stop the spread of disease, without it, the instances of tree loss throughout the City would be greatly magnified.

Dutch Elm Disease
Dutch elm disease is a fungal disease spread by the elm bark beetle. Once an infected elm tree is identified, it is marked, (usually with a green dot or ring on the trunk), and the property owner is notified. Property owners are responsible for removing diseased trees at their own expense within three weeks of notification. This time period is essential because the entire tree will quickly be colonized by more elm bark beetles, which mature quickly and are able to further spread the disease to other elms in the area.

Dutch elm disease may also spread through connected roots from one elm to another. In this instance, it may be advisable to mechanically sever the roots as soon as possible before the infected tree is removed.

Chemical Treatment
As stated earlier, removal of infected elms protects the remaining healthy elms. Individual elms can also be protected with fungicide injections. Many years of performing such a procedure has shown a high rate of success. The expense of this procedure, which typically needs to be repeated every three years, may limit its feasibility.

During the summer months, the City Forester routinely inspects the community for Dutch elm disease. Residents are also encouraged to watch their own elms. If Dutch elm disease is detected early in an infection stage, it is possible at times to prune it out. Typical symptoms to look for are yellowing of leaves -- usually in the upper crown -- followed by leaf browning, curling and falling to the ground. If residents suspect Dutch elm disease, they may call the City Forester for an inspection.

Oak Wilt
Unlike Dutch elm disease, oak wilt is thought to be a native disease. It affects oak trees primarily in the Midwest. The greatest concentration in Minnesota is in the seven-county metropolitan area.

Although oak wilt affects both the red oak group and white oak group, red oaks are most susceptible to this disease. White oaks are moderately susceptible and northern white oaks are the least susceptible. To distinguish between the two groups, note that red oak leaves have pointed leaf margins and lobes while white oaks have rounded margins and lobes.

Oak Wilt is spread in two ways. Most new infections are spread from diseased oaks into neighboring oaks through grafted roots. This can happen when surrounding oaks are within 50 to 60 feet of each other. Where feasible, the common control method in these cases is to mechanically break the root grafts using a vibratory plow. This must be done before the diseased tree is removed.

The other way oak wilt can be spread is through insect vectors that transmit the disease from oak wilt fungal spore mats to fresh wounds or cuts on healthy oaks. Oaks are most susceptible to new infections from April through June. Therefore, all pruning operations on oaks should be suspended during this period.

Most, but not all, red oaks killed the prior year can produce infectious spore mats under the bark during this critical period. These trees may not be kept, with bark intact. Residents are urged to use extreme caution when bringing in diseased oak wood to their property. The probability of starting new infection centers on their property or throughout the neighborhood is high.

Chemical Treatment
In high value white oaks, systemic injection with propiconazole by qualified arborists may protect nearby healthy oaks adjacent to infected oaks. It may also be a curative to white oaks exhibiting early symptoms of oak wilt.

Oak wilt is not the only disease affecting oaks in this area. Therefore, proper disease identification is necessary before devising any control recommendations. In Edina, the Kunde Company -- Oak Wilt control specialists -- are contracted to the State of Minnesota. They have the right to enter upon private property to conduct necessary inspections.

If residents observe unusual symptoms of their oaks, they may call the Parks & Recreation Department to arrange for an inspection.

Residents who wish to receive further information on this subject may contact the City Forester Luther Overholt at 952-826-0308.

© 2017 City Of Edina, Minnesota