Increasing Impact of European Elm Scale (Eriococcus spurius) in Calgary’s Urban Forest

Grayson Rathwell wrote:

I have lived in the City of Calgary since 2014 and have been gaining increasing familiarity with Calgary’s urban forests. I have observed that in certain areas elm trees (Ulmus spp.) are the most prevalent tree species used along sidewalks and boulevards. This is likely due to their ability to adapt to an urban environment (OMF, 2014), and the aesthetically pleasing canopy at maturity. Since 2014, I have noticed the bark and branches on many elm trees becoming increasingly dark in colour, I began investigating the source of this colour change. Upon closer inspection there was what appeared to be small oval shaped [insects] along the tree branches. The darker the trees branches, the more [insects] present.

After additional research, European Elm Scale [Insects] (Eriococcus spurius) were found to be the culprit. Elm Scale is an insect in the Order Hemiptera that feeds on elm trees and produces a black mold on the branches and can lead to stunted growth and may even kill weakened trees (Calgary Parks, 2019). Yellowing and thinned foliage was observed in several affected elms throughout Calgary. According to Mike Jenkins, a biologist with the City of Edmonton, Elm Scale is widespread throughout the province of Alberta (Edmonton Sun, 2017).

Over a relatively short period of observation, from roughly mid 2014 to the present, I have noticed a spread in both the range of elm scale and the severity of existing infections. As with several other environmental diseases and pests, it appears a changing climate has influenced its success (Rosenzweig, 2001). University of Lethbridge Geography Professor Stefan Kienzle, in an interview with CBC explained that the average growing season has increased between one to five weeks across Alberta since 1950 (CBC, 2016). As a changing climate continues to influence the severity of our winters, more elm scale can successfully overwinter in urban elms.

References:

Calgary Herald (2013, June). Calgary’s elm trees under attack; arborists urge war on pests. Retrieved from http://www.calgaryherald.com/life/calgary+trees+under+attack+arborists+urge+pests/8522133/story.html

CBC (2016, January). Alberta climate website lets you compare temperature and other weather changes since 1950. Retrieved from https://www.cbc.ca/news/canada/calgary/alberta-warmer-temperature-climate-change-kienzle-1.3390640

City of Calgary Parks (2019). Elm Scale. Retrieved from http://www.calgary.ca/CSPS/Parks/Pages/Planning-and-Operations/Pest-Management/Elm-scale.aspx

Edmonton Sun (2017, June). Edmonton elms under attack by elm scale infestation. Retrieved from https://edmontonsun.com/2017/06/08/edmonton-elms-under-attack-by-elm-scale-infestation/wcm/d8667db4-ffb1-4660-914b-a9905a7c4e5c

Ontario Ministry of Forestry (OMF) (2014, July). American Elm. Retrieved from https://www.ontario.ca/page/american-elm

Rosenzweig, C., Iglesias, A., Yang, X. B., Epstein, P. R., & Chivian, E. (2001). Climate change and extreme weather events; implications for food production, plant diseases, and pests. Global change & human health, 2(2), 90-104.