Recent media sources have reported that Dutch elm disease is back. Actually, it never left. Like a wildfire, it continues to smolder, and sends up occasional bursts, but nothing to rival the original conflagration. Some years are worse than others. In fact, many of the cases we are seeing now were infected last year. The symptoms of Dutch elm disease resemble a tree suffering from drought: Leaves turn yellow, wilt and begin to brown. This can be obvious, with dying branches and wilting leaves in a matter of weeks, or inconspicuous and easily overlooked when only on small twigs. Some trees take months, even years, to die. Others may succumb in a matter of weeks. When Dutch elm disease was introduced into the United States, it quickly spread across the country, killing hundreds of millions of trees and costing similar amounts in dollars. Today, many towns still have an Elm Street but no American elms. Minnesota was one of the last states to experience the epidemic. Fortunately, city foresters responded with aggressive management, and have preserved the legacy of the American elm. Fergus Falls boasts of retaining 70 percent of its original American elm tree population. Regular examination and prompt removal of infected trees prevents the infestation by elm bark beetles that spread this disease. It also prevents the disease from spreading root-to-root between trees. Additionally, early diagnosis provides homeowners with the option to treat infected trees. Treatment is not inexpensive, but neither is having a big, mature elm cut down and removed. Two fungicides are labeled for use on Dutch elm disease-infected trees: Arbortect and Alamo. Each must be applied by a licensed tree care professional. Early diagnosis and treatment have a high rate of success, providing trees with two to three years of residual protection. You can also protect healthy elms by having them injected with the same fungicides. Unfortunately, future epidemics are coming. In the last four months, one of the largest nurseries in the country accidentally shipped plants throughout the United States that were infected with the pathogen that causes sudden oak death. This disease has been shown to infect and kill native northern red oak and pin oak in addition to infecting 60 other plant species, with new species added monthly. So far there have been no incidences of infection found in Minnesota. In addition to diseases, there are a growing number of destructive insects working their way toward us from eastern states. Along with diseases, these insects have the potential to alter not only our landscape, but our ecosystems. As a state we need to prevent and contain them. Janna Beckerman is a plant pathologist with the U of M Extension Service.
