Dutch elm disease started to kill American elms in Winnipeg in the mid-1970s. Many thousands have succumbed to the disease, which reappears every year on at least 1,000 to 2,000 elms.
Last November, the federal Pest Management Review Agency approved a vaccine that has proved to be 99-per-cent effective against Dutch elm disease (DED) in Canada.
The vaccine is called Dutch Trig. It works in principle similar to the way flu vaccines work in the human body. Dutch Trig elicits or triggers a response that causes a defence reaction in the conducting cells of elms located just below the bark.
If the tree detects the presence of DED, it will quickly contain the disease and stop it from spreading during the year of injection. Like flu vaccines, the inoculation is good for only one year. The vaccine has been working in Holland since 1992, and in several areas in the United States since the late 1990s.
Dutch Trig is a liquid emulsion of about one million microscopic Verticillium fungal spores that will not do any damage to elm trees. Using a special tree injector, one 0.15 ml (0.005 ounce) droplet of Dutch Trig is placed under the bark. Injections are spaced about 10 cm (4 inches) from each other, completely around the circumference of the tree at about 1.4 m (4.5 feet) above the ground.
Timing of the injection/inoculation is critical. There is about a six-week window in early to mid-spring when the injection will be effective. Injections made later into the summer have been shown through research to be ineffective. The best time to inject is when the elm leaves are just opening up from their winter buds. This normally occurs in May, but this year's early spring will force the leaves out earlier. It's very important to schedule clients who want their elms inoculated as soon as possible.
The injection/inoculation work is a joint venture of Viburnum Tree Experts (204-831-6503) and Perennial Trees Inc. (204-896-0404). It takes some time to schedule properties requiring this service as elm trees must be assessed, measured and price quoted in advance of the injections. Please call one of the above numbers for further information.
Remember, to prevent your elm from getting Dutch elm disease, there is only a six-week period that the work can be carried out.
Mike Allen is a consulting urban forester, certified ISA arborist and owner of Viburnum Tree Experts. He provides advisory services on tree and shrub problems through home visits and regularly gives courses on tree and shrub care. He can be contacted by calling 204-831-6503 or emailed at viburnumtrees@shaw.ca Visit his website at www.treeexperts.mb.ca for further information.
