Dutch elm disease is caused by the fungus Ophiostoma not-ulmi, which invades the water-conducting vessels of elms. The leaves of trees wilt, turn yellow or brown and then fall. Another diagnostic feature is the formation of brown or green streaks in the infected sapwood. This discoloration is visible when the bark is peeled back on symptomatic branches. Most elm species are susceptible to this disease.
Disease cycle of Dutch elm disease
The fungus is spread by elm bark beetles which feed on and breed in elm trees. The fungus also can spread to adjacent healthy elms through grafted root systems.
Type of Sample Needed for Diagnosis and Confirmation
The Iowa State University Plant & Insect Diagnostic Clinic can help you to investigate and confirm if you plant has this disease. Please see our website for current forms, fees, and instructions on collecting and packing samples. Contact information for each states diagnostic laboratory for U.S. residents. If your sample is from outside of Iowa please do not submit it to the Plant & Insect Diagnostic Clinic without contacting us
We are looking for a very specific sample; please follow these instructions as much as possible:
- Select 3 to 6 living branches from the symptomatic area in a tree.
- Select branches 1-2 inch in diameter (we need branches, not twigs) and 6 to 12 inches in length.
- Check for sapwood discoloration as shown in figure 4 of the publication “Dutch Elm Disease.”
- The twigs with discolored sapwood are what we are looking for.
- Collect the sample only when you can either deliver it directly to the PID Clinic right away or to send it overnight (never on a Friday!).
- Follow our submission instructions on the Clinic website http://www.ipm.iastate.edu/ipm/info/submit/plant
- Place your completed submission form along with the samples in a crush proof box.
- How to drop off or mail the sample visit http://www.ipm.iastate.edu/ipm/info/submit/plant
- Submission form and current fees, visit: http://www.ipm.iastate.edu/ipm/info/contact
In some cases the help of an arborist is needed to collect branches if they are out of reach. For information on how to choose and arborist see the resource https://store.extension.iastate.edu/Product/Choosing-an-Arborist
Management of Dutch elm disease
Sanitation, the removal and proper disposal of all dead or dying elms, is the key to successfully managing DED. This involves early identification of the disease and immediate removal of infected elms. Prompt debarking, chipping, burning, or burying elm wood makes the wood unsuitable for beetles. Management may also include root graft disruption, the breaking of root connections between diseased and healthy trees to prevent the fungus from spreading from tree to tree through root grafts.
Therapeutic pruning is the removal of infected portions of an elm and is effective only if the elm has been inoculated by beetles. If the fungus is on the main stem or has come into the tree through grafted roots, pruning will not be successful. Systemic fungicides, when properly injected into elms inoculated by bark beetles, may save trees in the early stages of Dutch elm disease when less than 10 percent of the crown has wilted. These chemicals are injected into the root flares by a certified pesticide applicator.
For more information see this bulletin about Dutch Elm Disease.