LDD moth outbreaks could decline in Dufferin this year: CVC

Written By Paula Brown

Local Journalism Initiative Reporter

As warmer spring weather arrives in Dufferin County, residents might find their trees home to a reappearing pest. 

The Ontario Ministry of Northern Development, Mines, Natural Resources and Forestry (NDMNRF) is predicting an increase in population of the Lymantria dispar dispar (LDD) moth, also known as the spongy moth, across the province this year. 

“That's largely due to the fact that there are some areas on large swaths in sort of northern and eastern Ontario that are in year one or two of an outbreak,” said Bryana McLaughlin, coordinator of the invasive species and habitat structure programs for the Credit Valley Conservation Authority (CVC). “They're expecting that those areas will expand for most of the CVC watershed and probably into Dufferin County.”

While a population increase is predicted for across the province, in Dufferin County the population could possibly be on a decline as areas enter year three to four of an outbreak of the tree pest. 

“Now, that doesn't necessarily mean that every single area is going to see a decrease, we're noticing that the egg mass numbers are quite patchy, at least across the CVC watershed when we did our surveys at the end of 2021. There are some areas where the egg mass numbers were extremely light and select pockets where they were fairly high,” said McLaughlin. 

The LDD moth, also known as the spongy moth, following a recent name change, is a naturalized invasive species that eats the leaves off of trees sometimes completely to defoliation. The insect species was brought to Canada as part of the silk trade and later escaped to the natural environment. Spikes in population of the moth occur around every seven to ten years, and it is during these spikes, which typically last between three to five years, that problem in declining tree health and mortality can happen. 

“In large forests, the impact kind of gets spread out over all the trees, but as you can imagine in urbanized areas or people's backyards, or in parks, the stresses that the trees are experiencing are a lot higher with drought, compaction, salts, and heat stress,” said McLaughlin.

She added, “Another major stressor for several years in a row can cause a lot of tree death in these types of areas.” 

McLaughlin noted that there are specific signs occurring to suggest the decline in LDD moth population in pocket areas of the CVC watershed, which includes the southern most part of Dufferin County. These signs include the presence of the virus and fungus that infects the moth, their eggs being preyed upon and natural predators. 

Climate change and milder winters has played a contributing factor in LDD moth outbreaks, and despite what felt like a colder winter, McLaughlin said they expecting minimal decline in egg mass due to the cold. 

“Although the weather did get cold, we didn't see that sustained cold period such as -20 degrees Celsius for a couple of weeks in a row. The reason the cold kills LDD is because when it gets too cold the eggs freeze so if they're below snow cover or on the side of a warm building those will still hatch being buffered a little from the temperature. We're expecting that there probably will be some that were killed by the cold, but not all of them,” said McLaughlin. 

As we enter early April, residents will be able to take early precautions to remove LDD moth egg masses before they hatch. 

LDD moths prefers trees such as oaks, maples, willows and poplar, and also prefer warmer areas such as slopes, higher elevation, and areas with rolling or hilly terrain. 

Tips for residents that find their trees home to the LDD moths include removing the egg masses by scraping them from areas such as trees, patio furniture, houses, and garages between the end of October to early April, and putting them in a container of soapy water for a couple days before disposing of. 

McLaughlin added that people have used shock vacuums as an innovative way to remove the eggs from the tree quickly. 

If you don't remove the eggs before they hatch another way to remove the LDD moth is banding the trees with a folded length of burlap between May and July. 

McLaughlin said the caterpillars of the LDD moth will seek shelter in the burlap and will make it easy to pick them off. 

“Both methods, especially when you do them together, can be pretty effective in protecting individual trees,”
said McLaughlin. 

For those with larger property are forested areas it is recommended to focus on the edges of the forest. 

“We've noticed significant differences when we're doing our surveys that the edges of the forest are a lot harder hit than say the interior of the forest property,” said McLaughlin.