Dutch Elm Disease: Monitoring, Testing, Removal, and Replanting
Eastmoreland Elms Lost to DED: 2014–six and counting; 2013—one; 2012—two; 2011—13; 2010—10….
Monitoring…Every summer, from May to October, the Urban Forestry Department of the City of Portland sends out a Dutch Elm Disease Monitor. This person is charged with reviewing the City’s elms and facilitating the removal of dead or dying elms infected with Dutch Elm Disease. Once popular street trees, elms have largely disappeared from cities and towns, due to Dutch elm disease. Portland is fortunate to still have many large mature elms, and removing diseased elms helps to slow the spread of DED.
Urban Forestry has maps of all the elms in the City and records of previous locations where Dutch Elm Disease (DED) has been diagnosed. The Elm Monitor visits all these locations looking for signs of DED. The most typical symptom is brown, dry, curled leaves on a branch, called flagging. This is usually a location where a bark beetle carrying the Dutch elm disease fungus (Ophiostoma) has been feeding and transmitted the pathogen. This browning of the leaves will progress down the branch as the fungus moves through the elm. Residents who suspect DED is present and the Elm Monitor has not posted the tree can email email@example.com to report the tree’s address and location.
Testing…When the Elm Monitor finds symptoms of DED, a sample is taken. A sample consists of 4 to 8 branch segments, 6 to 8 inches long and at least .5” in diameter. The bark is peeled back and the wood is inspected for brown to grey streaks. If streaking is visually identified, but diagnosis is inconclusive, the sample is sent to the OSU Plant Pathology Lab in Corvallis for testing. Segments of the sample are cultured by the lab and if they grow the Ophiostoma fungus, the elm has tested positive for Dutch elm disease.
Removal of Trees and Disposal of Wood…Once an elm tests positive, it must be removed as quickly as possible to prevent the spread of the fungus. Urban Forestry is currently funded to remove elms with Dutch elm disease that are between the sidewalk and the curb – ie in the public right-of-way. Elms that are on private property are removed by the property owner.
For elms in the right-of- way, an Urban Forestry Division Tree Inspector coordinates the removal and replanting of that location. The Tree Inspector marks the curb and the tree with paint and posts a notification on the tree, stating it will be removed due to DED. If high voltage power lines are present around the tree, the Inspector schedules the tree to be cleared from high voltage lines by the utilities. The Inspector then generates the work order for an Urban Forestry tree crew to remove the tree.
The Urban Forestry tree crew normally handles large removals like this in stages. First the crew will come and ‘brush out’ the elm using a bucket truck to remove all the smaller limbs, leaving the large main branches. Then a large crane will be used to bring down the main branches and the trunk. Last the stump will be ground, usually at a later date.
For both infected elms removed by city crews in the public right of way and by arborists working on private property, the diseased wood must be disposed of according to administrative rules set by the Oregon Department of Agriculture. Proper disposal is described in the attached document from Portland Parks and Recreation, Urban Forestry Division.
Required Replanting…With an eye to preserving the urban forest in the right of way, the property owner is required to replant a tree in that spot. Typically, the planting permit is issued at the time of removal and the City Tree Inspector provides the adjacent property owner with a Tree List approved for the site conditions—the presence of overhead wires, underground utilities, and planting strip width. It’s an opportunity to choose a new, large canopy tree where no high voltage lines exist or a tree sized to flourish under high voltage lines or in a narrow planting strip. Typically, the planting permit stays open for one month; neighborhood plantings occur throughout the city during the winter, when it’s rainy and the best time to plant trees. For information regarding neighborhood planting, please contact Erica Timm: 503-467-2533 EricaT@FriendsofTrees.org