In last few years in Calgary, the problem of elm scale is getting bigger and bigger. The problem is even worst in public boulevard trees.
Crawlers begin feeding on leaves from May to June and later they migrate off of the leaves to overwintering sites on the twigs and branches. Elm scale feeds by piercing leaves and bark, and sucking juices from the tree. Heavy infestations may kill or weakened trees and cause branch dieback in healthy trees. Large amounts of honey dew are produced which eventually cause the leaves to be covered with grayish/black colored sooty mold. The sooty mold reduces the aesthetic appearance of trees and honeydew can become a nuisance as it coats patios, decks, and vehicles.