It is only about the length of a fingernail.
Yet a tiny insect is being blamed for the death of more than 100 million ash trees in Ontario and the U.S.
The emerald ash borer, an iridescent green insect pest believed to have been accidentally introduced from China, was first detected in the Detroit-Windsor area in 2002.
Since then it has spread, transported in infested firewood and nursery stock or by its own wing power, carried on the wind.
The emerald ash borer (EAB) reached York Region in 2008, Bradford West Gwillimbury in 2013, and now, said Simcoe County Forester Graeme Davis, “it’s essentially spread throughout Simcoe County. We didn’t carry out EAB trapping this year. There’s no need. It is here.”
White ash, black ash, green ash, pumpkin ash — of the five species native to Ontario, only the blue ash shows some resistance to the voracious bugs. The rest succumb within a couple of years, leaving bare branches and dead trees along roadsides and in forests.
The Ontario Ministry of Natural Resources estimates that EAB kills 99 per cent of the ash trees it infests — its larvae burrowing into the softer cambium below the bark, eventually girdling the tree and cutting off its supply of nutrients.
There is a treatment that has been effective, to some extent — an injection of TreeAzin, a natural product derived from the neem tree.
Unfortunately, it is an ongoing treatment that must be reapplied every one to two years at a cost of hundreds of dollars per tree.
With an estimated five to 10 per cent of Simcoe County’s forests comprised of ash tree species, treatment with TreeAzin is impractical.
“With the type of properties we manage, it’s not a viable option for us,” Davis said.
Instead, the county has taken a management approach, selectively harvesting ash trees in its hardwood forests, and planting replacement species. Ash trees that could pose a hazard, along trails and public use areas, are removed first.
Asked about the impact of the removal of ash from the ecosystem, Davis suggested there has been little impact on county forestry operations.
“Historically, there were some small pockets of ash planted in our hardwood forests,” Davis said, but of the 20 million trees planted by the county, “probably only a few thousands are ash.”
The bigger problem is in urban areas.
Ash, with its rapid growth, straight trunk and tolerance to a range of growing conditions, has been a favourite tree in urban forestry planning.
It is the municipalities that are struggling most, Davis said.
And then there’s the environmental impact.
“It really is unfortunate. It’s a minor component of the hardwood forest, but it’s an important part of the diversity,” said Davis. “It’s an issue.”
Within the Lake Simcoe area, EAB has been spreading for the past 10 years.
“We’ve seen the impacts across the watershed,” said Cory Byron, forestry program co-ordinator with the Lake Simcoe Region Conservation Authority.
In some areas of Georgina, forests can be up to 80 per cent ash. In locales like Scanlon Creek Conservation Area, the percentages are closer to 10 to 20 per cent, he said.
But still, he added, “we’re talking thousands of trees. A huge portion of those ash are going to die out.”
Like the county, the conservation authority looked into costs and decided that treatment was not an option.
“For us, the best and most cost-effective process was a management strategy to remove and replace,” Byron said. “We’ve seen extremely heavy EAB infestation in the Lake Simcoe watershed.”
The conservation authority has been removing “hazard trees” — those along trails, near buildings and picnic areas, anywhere the public gathers — but plans to allow trees deep within the forest to die off, and remain as part of the natural habitat, Byron said.
And in response to both climate change and invasive species like the emerald ash borer, the conservation authority has taken a new approach in its planting programs. “We’re making sure we plant a huge diversity of species,” Byron said. “We’re trying to add resilience by adding diversity.”
The conservation authority is also adapting its tree-planting programs to specifically assist property owners of more than 0.8 hectares to replace trees lost to EAB.
There is no money at the municipal, county, provincial or federal level to help landowners with dead tree removal.
It is only at the municipal and private level that application of TreeAzin becomes a practical solution in an attempt to save at least the significant ash trees in the urban landscape.
Bradford West Gwillimbury began inventorying its ash trees more than five years ago, classifying trees on municipal lands based on their value to the urban environment. Those identified as worth preserving were treated with TreeAzin.
It is a plan that seems to be working, said Terry Foran, BWG director of community services. “It’s doing its job, from what we can see. We haven’t lost any ash trees in the last two years. We’re sustaining.”
But whether that will be maintained has yet to be seen, although there is an annual budget to cover treatment costs.
Where the battle against EAB is being lost is in the rural areas, in forests and on private lands. Few private citizens are investing in the costly treatment.
There is a sense that EAB will continue to devastate ash populations — a pattern that Ontario has seen before, with other blights introduced into the native forest.
“It was a different landscape after Dutch elm disease, and a different landscape after chestnut blight,” said Byron. “It’s going to be a different landscape after EAB — and, unfortunately, it’s not going to be the last.”
Climate change and new invasive species will have similar impacts in the future, he said.
Davis suggested there could be an alternative scenario.
“The longer term on this thing is hard to predict,” he said. There is the typical spike in tree deaths, but it is possible that EAB “essentially will eat themselves out of house and home,” and eventually come to some kind of equilibrium in the environment.
There is also research into the use of pheromones to disrupt the mating of emerald ash borer, and into the use of fungal agents and biocontrols.
The federal government has plans for a controlled release of parasitic wasps known to prey on EAB, but, Davis said, even if it works, “it’s not going to be a quick fix.”
Is there an infestation of emerald ash borers on your property?
The adult insects are a bright iridescent green, but they are hard to spot. Look for the characteristic D-shaped holes in the bark of ash trees, made when the adults emerge between June and August, and for die-back of the upper branches, new bushy shoots sprouting from the base of the tree, and increased woodpecker activity.
There may also be seven- to 10-cm cracks in the bark on young trees, and larval galleries observed beneath the bark.
Treatment with TreeAzin should be started before an infestation takes hold. And dead ash trees on urban lots should be removed.