The emerald ash borer, Agrilus planipennis, is a destructive insect pest that has left tens of millions of dead ash (Fraxinus spp.) trees in its wake. Since it was accidentally introduced to North America in the early 1990s, it has spread from Michigan, where it was first detected, to 20 U.S. states. In Canada, it was first detected 11 years ago in Windsor, Ont. and has spread to several neighbouring counties and now into Quebec. The pest has yet to arrive in Saskatchewan, but it's on the move. The closest known location is St. Paul, Minn.
Adults are small (half inch long) and sport a green metallic sheen, with a bright metallic red upper surface of its abdomen. Females lay 60 to 90 eggs, from spring through July. The tiny eggs, laid in bark crevices and seldom seen, are only 1/32 inch in diameter. They are white initially, but soon turn orange-red. The eggs hatch into white, segmented larvae that bore into the inner bark and cambium, creating serpentine (S-shaped) galleries or tunnels beneath the bark. They feed from late June through October. Even branches and trunks as small as one inch have been infested. The pupae gradually take on the appearance of the adult beetle and emerge through D-shaped holes in the bark, from mid-June to mid-July. The adults live only three to six weeks, mating and feeding on foliage. In colder areas they take two years to complete their life cycle.
Trees die because the galleries in the phloem tissue interrupts nutrient and water flow. The first symptom is crown dieback. Death occurs within two to five years, depending on the density of the infestation and the tree's size and health. The most obvious symptom of an infestation is dieback of the crown of the tree with young stems (adventitious growth) sprouting from the trunk where they would normally not be seen. These symptoms usually appear after a tree has been under attack for about three years. Woodpeckers may be attracted to borer infested ash trees.
All ash trees, both healthy and stressed, are susceptible to attack by the emerald ash borer: green ash (Fraxinus pennsylvanica), black ash (Fraxinus nigra), white ash (Fraxinus americana), Manchurian ash (Fraxinus mandshurica) and hybrids. Mountain ash, a Sorbus species, is not a true ash and is not susceptible.
Ash is an important tree in most Canadian urban centres. In Saskatoon, there are approximately 27,500 green, black, white and Manchurian ash trees, making up approximately 30 per cent of Saskatoon's tree inventory. In addition to the city's tree inventory, there are many additional ash trees on private property and within naturalized parks.
The U.S. Department of Agriculture and the Canadian Food Inspection Agency are taking a two-pronged approach. First, a ban on transporting all ash materials (logs, branches, wood chips) and all species of firewood from affected areas has been implemented in order to slow down the spread. The second prong is a longer-term approach using biological control agents. The USDA has identified three species of stingless parasitic wasps from China that attack either the larvae or the eggs of the EAB. All three have been released in several of the affected states. In Canada, the CFIA has only recently approved releasing two of the parasitic wasp species. One of the species, Tetrastichus planipennis, has been released in limited areas in southern Ontario to start.
The CFIA is also running a national monitoring program for the emerald ash borer. Twenty traps have been placed throughout Saskatchewan including two in Saskatoon. The City of Saskatoon is supplementing the CFIA program with an additional six traps. The green prism traps are coated in tanglefoot and are baited with a hexanol lure to attract adult borers.
The number one action you can take to help limit the spread of the borer is to not transport firewood, especially if vacationing in affected areas. This approach has been relatively successful in controlling the spread of Dutch Elm Disease. So hopefully, it will be years to decades before the emerald ash borer starts calling Saskatchewan home.
- Sara Williams is the author of the newly revised and expanded Creating the Prairie Xeriscape. This column is provided by the Saskatchewan Perennial Society.
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