2021 Will Be Remembered as “The Year of the Gypsy Moth”

beige Gypsy moth egg masses in groups clinging to the bark on the undersides of branches and on the trunk
Gypsy moth (Lymantria dispar) egg masses adorn many of the trees in urban and rural southern Ontario this spring. Unusually warm temperatures have supported the rapid growth of developing larvae inside these egg masses. (Photo: Jen Llewellyn)

Winter and early spring scouting for Gypsy moth egg masses has indicated EPIC levels of the moth larvae can be expected in much of southern Ontario this year!

Check out my Gypsy Moth Webinar by clicking on the video above!

In 2020, the Ontario Ministry of Natural Resources and Forestry (see above) observed record-breaking areas of defoliation in southern Ontario since the moth’s introduction over 50 years ago. Nearly 600,000 hectares of trees were defoliated by this pest last year, beating the original record of 350,000 hectares in 1991.

Although over 300 species of trees have been identified as hosts of the Gypsy moth, they are mostly likely to be found feeding on the foliage of Acer (except Acer rubrum), Betula, Fagus, Quercus, Populus, Prunus, Salix, Tilia, and the evergreen, Picea pungens.

overwintered, faded, Gypsy moth egg mass on paper birch bark
Gypsy moth egg mass on paper birch, note how egg masses lose their brown pigment after the winter, making them more difficult to detect. (Photo: Jen Llewellyn)
Gypsy moth egg mass on Norway maple bark
Gypsy moth egg mass on Norway maple bark, note how faded in colour the egg masses appear after winter. (Photo: Jen Llewellyn)
Gypsy moth egg masses on paper birch
Gypsy moths will lay their eggs on any available surface, even exfoliating bark. Adult females are unable to fly and are so heavy with eggs they cannot travel very far from where they pupated. (Photo: Jen Llewellyn)
Gypsy moth egg mass in spring
Overwintered Gypsy moth egg mass showing empty egg cases where parasitoid wasps have emerged after feeding on larva (photo: Jen Llewellyn)

Get ready to manage young larvae (black head capsule, less than 2.5 cm long) with foliar applications of  the bioinsecticide Bacillus thuringienesis subsp. Kurstaki (B.t.K., Bioprotec, Dipel, Foray, ReVokBTK, Thuricide HPV, Thuricide 48LV). High value trees may also be injected with TreeAzin (see label for directions). Later instar larvae may be managed with products containing permethrin (e.g. Dragnet in the landscape, Pounce etc. in the nursery) or spinosad (e.g. Success). See the MOECP “Allowable List” for pesticide applications in Ontario by CLICKING HERE.

IN THE COMING WEEKS: Larvae will be maturing, like this one from 2019

IN THE COMING WEEKS: First instar Gypsy moth (Lymantria dispar) larvae will likely be hatching (like these above from 2019) earlier than usual this spring, due to unseasonably warm temperatures in the last several weeks. 

First instar larvae from May, 2020

After hatching, larvae will climb to the top of the tree, produce a silken thread and take a ride in the wind in hopes of landing on a delicious botanical host.


bugfinderlogoFor great images and management information check out our FREE scouting App Bugfinder, on Apple and Google Play!

About Jen Llewellyn

OMAFRA Nursery and Landscape Specialist @onnurserycrops
This entry was posted in Arboriculture, Insects, IPM, landscape, Weekly Nursery Landscape Report and tagged , , , , , . Bookmark the permalink.

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