The Gleaner

Gypsy moths invade the Haut-Saint-Laurent

Eight producers in Ormstown, Franklin and Saint-Chrysostome recently joined forces to have a pesticide, Bacillus thuringiensis kurstaki (BTK), applied by helicopter to 500 acres of maple groves and orchards in an attempt to control the European gypsy moth.

This tree-defoliating caterpillar has a marked preference for oak foliage but will happily devour the leaves of more than one hundred other species such as sugar maples, apple trees, blueberries and even vegetable plants, eating up to one square metre of foliage in its lifetime.

Apple and maple syrup producer Jeff Blair, who helped initiate the large-scale application of the pesticide, explains that after seeing his maple trees lose their leaves in 2020 he didn’t want to take any chances this year. “It was ground zero. There were caterpillars everywhere, and by the time they finished eating the leaves off the trees, they were on the understory plants,” he says.


Jeff Blair in his orchard, which has been damaged by an invasion of gypsy moth caterpillars (shown below).  PHOTO Mylaine Massicotte


At Blair Orchards, egg sacks were clearly visible on the maple trees: a sign that without treatment, the grove would again have been defoliated. The foliage of the apple trees suffered more damage, as Blair opted to wait for the bees to finish their important work in the orchard before he proceeded with the application of BTK, which took place on May 29.

The pesticide consists of a bacterium which, when applied to leaves, kills caterpillars as they ingest it. It is approved for use in organic farming and does not affect other insects or animals. It was registered for aerial spraying at the time it was applied locally; however, this is no longer the case, which makes it near impossible to treat whole maple groves. Producers and citizens are now forced to spray from the ground.

The presence of this caterpillar has been observed throughout the Montérégie, but more specifically in the southwest part of the region. René Dulude, a forestry engineer, notes that the presence of egg sacks was significant this spring. His observations suggest that while infestation sites are quite localized, the trees in areas where the caterpillars are present will likely lose up to 80 per cent of their foliage.

Marianne Cusson, a biologist with the Agence forestière de la Montérégie (AFM), says that a mature and healthy tree is resilient and can leaf out again. However, this requires considerable energy from the tree, which will see its growth reduced.

Cusson emphasizes the importance of regular forest management to remove damaged trees; this allows healthy trees to grow, and it also supports diversity of species and as well as the age of a stand. She notes that if maple producers are not able to intervene with pesticides, they should reduce their number of taps to help the trees to recover, which represents a potential loss in yield that is not covered by crop insurance.

For more information on the European gypsy moth and its life cycle, as well as control methods and natural predators, visit

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