Guarding against Dutch elm disease will take neighborhood wide attention

By Linda Bell
Special to the Viewpoint

The recent loss of several elms in Curtis Park and along streets such as Fourth Avenue, 22nd Street, and Donner Way reflects the doubling of confirmed cases of Dutch elm disease in Sacramento. These losses have made neighbors increasingly aware of the vulnerability of an aging urban forest, especially one whose canopy is comprised of one type of tree, making for especially susceptible disease conditions.

Questions from neighbors concerned with how to protect their elms and what happens once a tree is infected, spurred SCNA's Neighborhood Concerns Committee to recently form a special Tree Subcommittee. The subcommittee plans to provide answers in coming months through workshops, established tree programs and more articles in Viewpoint.

The Dutch elm disease cycle has three components: a susceptible host tree population (elm family), a transmitter (bark beetle and/or root grafts), and a fungus. The fungus spreads to new tree hosts as spores on beetles or in the water conducting system of root grafts with nearby infected trees. The infection results in a blocking of the water conducting system and weakening of the tree which eventually leads to death.

The first signs are wilting or drooping green leaves which later turn brown and wither. These signs in the outer, upper canopy are usually due to beetles, while those along the lower trunk are from root grafts. Root graft infections tend to spread more quickly, and are one reason so many of our closely-spaced street elms have been lost recently.

Improved health of our elm tree population combined with early detection of trees susceptible to, or in the early stages of, the disease can confine the spread of disease and increase treatment options. Various professional methods, such as limb pruning, root barriers, etc, have been used to arrest the disease, but these are all tree and site specific, with varying levels of effectiveness. An internet search for Dutch elm disease can provide information. Any work on traffic strip trees done by arborists, other than the city, must have a permit from the city.

Notification and detection of Dutch elm disease
At the first signs of Dutch elm disease, notify the Sacramento Urban Forest Division at 808-6345. An arborist will inspect the tree and take samples for lab confirmation. Other conditions can have symptoms similar to Dutch elm disease. If infected, a tree is tagged and the property owner notified.

Removal of diseased trees
If the disease is too extensive, the tree is girdled (a cut is made around the base of the tree) and is cut down as soon as possible to reduce spread by beetles. All wood from the infected tree is removed and properly disposed. Any wood with the bark intact can spread the disease. The stump is ground and soil added if needed.

Replanting after tree removal
The city provides a selection of trees which are planted in the fall when conditions are best for establishment. Except under power lines, the city replants large shade trees to cool houses and streets. Planting a mix of tree species or cultivars helps avoid the susceptibility of monocultures. Even Dutch elm disease-resistant cultivars should be mixed on a street to guard against new strains of the disease.

How to improve tree health to guard against susceptibility
Monthly deep watering and mulching is essential to tree health. Prune out dead wood, but not in spring and summer when beetles are active and attracted to fresh cuts. Avoid or minimize damage to tree roots when installing irrigation systems or hardscapes. Impervious hardscapes (cemented pavers, etc) reduce soil aeration and water percolation. The Sacramento Tree Ordinance does not allow park strips to be filled with hardscapes.

Treatment with fungicides, such as Arbortect, can act as a preventive, not a cure. A new fungicide, ArborFos, is being tested in Curtis Park

To aid detection efforts, the Sacramento City Urban Forest Service department has joined with the Sacramento Tree Foundation to educate citizens about Dutch elm disease. Neighbors can be especially good at finding infected trees tucked in alleys and yards. Two Sacramento Tree Foundation programs, Save the Elms and Neighborwood, can help our community establish an elm survey and evaluation. Such a survey can provide a baseline for determining the health of our trees, noting any changes in their condition and planning future actions.

To volunteer for the tree survey group or ask more tree questions, contact the SCNA Tree Subcommittee through the Sierra 2 office at 452-3005.

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