The Invasive Species Centre has a wealth of informative fact sheets and papers on their website at https://invasivespeciescentre.ca/invasive-species/invasive-species-resources/
We wanted to share these fact sheets about the European Gypsy Moth and management practices, since May and June are when we see those EGM caterpillars on maples and other trees.
Timely excerpts from these resources:
IMPACT of the European Gypsy Moth:
- A single gypsy moth caterpillar can eat one square metre of leaves in a season
- Repeated defoliation makes trees susceptible to other pests and diseases, and can eventually lead to tree death
- Defoliation in orchards can increase vulnerability to agricultural pests and diseases and can negatively impact farm stock
- Loss of species in natural areas can affect biodiversity and forest wildlife
How to manage European Gypsy Moth Caterpillars
(April through June):
For private homeowners, BTK (Bacillus thuringiensis kurstaki) is available for purchase from local hardware stores to use against EGM. This biopesticide can be applied by a registered pesticide application company or by homeowners who have carefully read application instructions. BTK is a product that affects the digestive system of caterpillars and should only be applied between May and early June, when EGM are still in the larval (caterpillar) stage. Two spray applications are usually required for effective control. Application of BTK after mid-June is not an effective way to manage EGM.
On a larger scale (multiple properties or a forested area), Btk should only be applied by a professional pesticide application company and is most effective when supported by a team of landowners, landowners’ association, or municipality looking to manage EGM.
Gypsy moth populations are also affected by a number of pests, including mice, birds, wasps, and a specific fungus and virus. The fungus and virus are believed to be the reasons gypsy moth populations crash for ten or more years.
Caterpillars can be successfully trapped using burlap. Start by wrapping a 45 cm (18 in) wide strip around the tree at chest height. Tie a string around the centre and fold the top portion down to form a skirt, with the string acting as a belt. Pick off the caterpillars daily and dispose of them (see hand removal above).