Hundreds of insect traps have been set up around Edmonton so city pest management staff can monitor any threat to the city's urban forest.
"About half of our street trees are green ash and the other half are American elm so between the two of them there's a lot of vulnerability there," said Mike Jenkins, biological sciences technician with the city of Edmonton.
Two of the most destructive pests in North America go after those two tree species, which are a huge asset to the city, Jenkins said.
"Edmonton has the largest stand of Dutch elm disease-free elms in the world," he said. "We have about 60,000 city-owned trees and about 30,000 privately owned elms."