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LDD (Gypsy) Moth Management

June 1, 2021

About LDD Moths

European Gypsy moth, Lymantria dispar (LDD), is a non-native invasive pest that was introduced in the late 19th century. It was first discovered in Ontario in the 1960’s and has been a major defoliator of deciduous and coniferous trees across Southern Ontario.

Through monitoring efforts, our terrestrial ecologists have been able to identify hotspots for LDD moth egg masses along the south shore of Cootes Paradise Marsh and at Rock Chapel nature sanctuary. The fuzzy brown egg masses were laid this past summer and are waiting for enough accumulated warmth for the caterpillars to emerge. In each egg mass there can be up to 1,000 eggs!

The larvae (caterpillars) of the LDD moth feed on the leaves of hundreds of trees and shrubs but tend to prefer oak trees. Since oaks are a staple in the Carolinian forest, these non-native pests are threatening this unique ecosystem.

LDD Moth Adult (Female)
LDD Moth Adult (Female)
Egg Masses and Pupa on Tree
Egg Masses and Pupa at the Arboretum
Helicopter flying over trees spraying for insects
Helicopter flying over trees spraying for insects.

2021 LDD Spraying

Between May 24 and June 4, 2021 a low-flying helicopter will be applying a total of four aerial sprays to mitigate LDD moth outbreak will take place over Royal Botanical Gardens’ (RBG) natural land properties of Rock Chapel and Cootes Paradise south shore. Spraying will be isolated to these two areas.

Spraying will be conducted by Zimmer Air Inc. using bio-pesticide Btk.  Precise timelines of the spray are weather dependent and RBG will communicate spray dates through social media prior to each spray. Sprays will occur over 2 days and take place in early morning between 5 and 9 a.m. The helicopter used for the spray applications will be flying low. Rock Chapel and Cootes Paradise south shore will each receive 2 spray applications. RBG will post notices at entrances to trails that are within spray zones. Rock Chapel and Cootes Paradise south shore will each receive 2 spray applications. Actual spray dates will be posted on RBG’s Facebook and Twitter.

RBG’s contractor will be applying a Class B pesticide, Foray 48B Biological Insecticide Aqueous Suspension, Registration No. 24977 under the Pest Control Products Act, with active ingredient Bacillus thuringiensis subspecies ‘kurstaki”.

In RBG’s cultivated garden areas, staff eradicate egg masses through hand removal, scraping egg masses off tree surfaces and placing them in soapy water.

Learn more about RBG forest areas and conditions.

Confirmed Date(s)/Time: Tuesday, May 25, 2021.
Cootes Paradise South Shore: 5:30 a.m. to 6:30 a.m.
Rock Chapel: Approximately 7:30 a.m.

Tuesday, June 1, 2021
Cootes Paradise South Shore: 5:20 a.m.
Rock Chapel: Approximately 8:30 a.m.

2021 Spray Zones

Satellite map highlighting the LDD moth spray zones along the south shore of Cootes Paradise
Satellite map highlighting the LDD moth spray zones: Rock Chapel and the south shore of Cootes Paradise.

About Btk

Bacillus thuringiensis ‘kurstaki’ (Btk) is a soil-borne bacterium that is applied to the leaves of affected trees while caterpillars are in their early stages of development. Once ingested, the bacterium disrupts the caterpillars’ digestive system with cessation of eating within 24-48 hours. Within days, caterpillars that have ingested Btk will succumb to its effects.

Btk does not have any negative effects to humans, birds or bees. Btk will affect other caterpillar species (known as non-target species). Due to its low residual nature and the narrow spray window of pest development, the non-target impact is expected to be low.

Individuals who have concerns should take reasonable precautions to avoid exposure during a spray program in the same way they would avoid pollen or other airborne materials during days when air quality advisories are issued. Residents can also reduce exposure by staying indoors with windows and doors shut during the spray period if spraying is taking place in their area, although this is not required by health officials.

Tree Skirting

Tree skirting is another method RBG uses to protect leaves from being eaten by caterpillars without harming other creatures. LDD moth caterpillars typically feed during the night, and during the day they seek shelter on the ground. When they climb back up the tree to feed, they end up trapped under the skirt. By stopping the LDD moths in their caterpillar stage, they can’t breed and contribute to future generations of moths.

LDD caterpillar caught in tree skirt in Hendrie Park (from 2017)
LDD Moth caterpillar caught in tree skirt in Hendrie Park (from 2017)
Tree skirt around trunk of an Oak Tree in Hendrie Park (from 2017)
Tree skirt around trunk of an Oak Tree in Hendrie Park (from 2017)

Further Resources

Visit the City of Hamilton or City of Burlington websites for more information on the spray programs for our local municipalities.