Gypsy Moth Update: June 18th, 2021

In 2020, the Peterborough District (which includes the Municipality of Clarington and Northumberland County) entered an outbreak of European gypsy moth (Lymantria dispar dispar) or LDD, and the outbreak has persisted into 2021. According to the Ministry of Natural Resources and Forestry (MNRF) 2020 forest health monitoring the LDD defoliation in Ontario increased from 47,203 hectares in 2019 to 586,385 hectares in 2020. The District with the largest area of moderate to severe defoliation of 159,578 hectares was the Peterborough District. To put that into perspective in 2019, Peterborough District only had 409 hectares of moderate to severe defoliation. This information is available on the MNRF webpage.


Although it is devastating to see our forests and street trees completely defoliated by the LDD, this is not a new pest for Ontario. LDD was first detected in Ontario in 1969, with no widespread defoliations occurring until 1981. Like most pest species, they have a boom and bust life cycle, meaning that every 7-10 years the population explodes resulting in extreme numbers of LDD; 2020 and 2021 are examples of this. Luckily it is not a losing battle as naturally, the population will bust. 


When the population is in high concentrations LDD are more susceptible to contacting a natural fungus or virus that will kill the caterpillars. Although they will die-off naturally, this process may take 3-4 years. While waiting for the species to naturally collapse, the woodland will be defoliated, making the area look barren.  However, trees can undergo defoliation and survive as long as they are in good health.  


A good way to ensure that your trees are healthy is to properly manage your woodland. Proper management of a woodland will remove the weak and dying trees, which will increase the resources such as sunlight and nutrients for the healthier trees remaining; this will make them strong and more resilient against pests and pathogens. Additionally by properly managing the woodland you will allow for natural regeneration which will allow for the growth of trees that may be better adapted for climate change. 


The Ganaraska Region Conservation Authority (GRCA) used funding from the 2020 Ontario Power Generation Regional Biodiversity Program to spray approximately 100 acres of red and white oak in the East (Ganaraksa) Forest. The area was selected because it contains very healthy, highly quality trees and was recently harvested to manage for the natural regeneration of oak trees. Due to the area being recently harvested and regenerating it is in a stressed state and would have been more susceptible to LDD defoliation resulting in death. 


Since the aerial spray, the red and white oak compartment contains trees with full crowns and minimal to no caterpillars observed. Adjacent compartments are almost completely defoliated, with heavy numbers of caterpillars observed. Although the GRCA did have a small compartment sprayed, of the 11,000 acre Ganaraska Forest, staff understand that approximately 90% of remaining woodland may be defoliated again. Although we are not too concerned, as our woodland is healthy and should be able to combat against the invasive predation. 


It is impractical to think that all of Southern Ontario could be sprayed to control LDD, especially since the population natural collapses after a few years. Also, it is important to remember that when dealing with any invasive species the goal is not necessarily eradication, yet management and control of the species. It is impossible to get rid of the LDD in our area, therefore we must ensure that are woodlands and trees are prepared for pests and pathogens by making sure they are managed properly, that they are diverse and that they remain healthy.  Good management never comes from taking a reactive approach; spraying for a pest is only a short term plan, whereas we need to be thinking about the long term plan and the large scale. 





Comp 134 - sprayed (1)
Comp 135 - unsprayed (5)