CALGARY – Plant specialists in Alberta are fearing the long-expected infestation of Dutch Elm disease will hit the province this spring.
The disease, often deadly, could affect thousands of trees in the province, says Calgary’s city entomologist Todd Reichardt.
It can kill an elm tree within three weeks or take as long as two years, said Reichardt. Alberta has American, Siberian and Brandon elms which are all susceptible.
The disease has devastated elms in other parts of North America, including Ontario, Manitoba and Saskatchewan. It is caused by a fungus which hitchhikes on the European bark beetle. As the beetles burrow into an elm, the fungus stays in the first layers of the tree and clogs the water-carrying vessels.
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“Effectively, it strangles the tree of water,” Reichardt said.
Dying trees attractive
Trees suffering from a dry season, or stressed from other problems, are more susceptible because the beetles are attracted to dying or dead trees.
The first symptoms appear when leaves in the summer curl and appear almost dead. Another symptom is a brown streaking color under the bark.
Farmers should monitor elm shelterbelts several times a year for signs of the disease and contact agriculture offices if problems are suspected. All dead and dying wood should be pruned. Burn the wood or chip it immediately. Do not keep it or sell it for firewood because the beetles will continue to live in the wood, said Reichardt.
Pruning should be done before April 1 and after Aug. 31, when the beetles are inactive.
Wrong time for pruning
“Otherwise, if you prune a tree in the middle of the summertime, you’re putting the tree under stress and it’s going to send out chemical signals to attract beetles,” he said.
Beetle-monitoring traps set in Calgary last summer caught insects in 20 out of 32 traps. Entomologists suspect the beetles came to Alberta via illegal firewood from the Great Falls, Montana area because they trapped the smaller European bark beetle which thrives in that area.
“We have a different species of insect than Manitoba or Saskat-chewan are dealing with,” he said.
Years of vigilance at the borders and a ban on imported firewood have kept British Columbia and Alberta free of the disease so far, said Reichardt.
The beetles don’t usually disperse more than 100 metres from where they emerged. They are weak fliers although some may drift with the wind. No insecticides appear to be effective.
The beetles aren’t expected to create as much destruction in B.C. as in other provinces, because there are few elms there.
