If you continue to find high levels of LDD moth in your area, report sightings through the online reporting tool. You can also report sightings by calling 311.

Aerial spraying operations have been completed. No further spraying is scheduled to occur. City staff will continue to monitor the treated areas throughout the year to evaluate the effectiveness of the aerial spray.

The LDD Moth (Lymantria dispar dispar), formerly known as European Gypsy Moth, is a non-native defoliating insect that feeds on a variety of tree species found in the Greater Toronto Area (GTA) and throughout North America. The City of Toronto’s management program focuses on controlling outbreak levels of LDD moth in areas with trees that are at risk of defoliation, typically oak dominant communities. Since LDD moth is firmly established in Toronto and North America, the complete removal of these insects is no longer a possibility.

Aerial spraying is weather permitting and typically happens between 5 and 9 a.m.

Dates Wards/Locations Status
May 24 19 (Beaches-East York), 20 (Scarborough Southwest), 22 (Scarborough-Agincourt), 23 (Scarborough North), 24 (Scarborough-Guildwood), 25 (Scarborough-Rouge Park) and parts of ward 16 (Don Valley East) Round 1 -completed
May 28 4 (Parkdale-High Park) Round 1 – completed
May 29 6 (York Centre), 15 (Don Valley West), 16 (Don Valley East), 17 (Don Valley North), 18 (Willowdale) and 21 (Scarborough Centre) Round 1 – completed
May 30 19 (Beaches-East York), 20 (Scarborough Southwest), 22 (Scarborough-Agincourt), 23 (Scarborough North), 24 (Scarborough-Guildwood), 25 (Scarborough-Rouge Park) and parts of ward 16 (Don Valley East) Round 2 – completed
May 31 4 (Parkdale-High Park) Round 2 – completed
June 3 4 (Parkdale-High Park), 6 (York Centre), 15 (Don Valley West), 16 (Don Valley East), 17 (Don Valley North), 18 (Willowdale) and 21 (Scarborough Centre) Round 2 – completed

Interactive Treatment Map

Use the interactive treatment map to find out if your neighbourhood is in a designated spray zone or to see if ground based treatments are planned for City-owned trees in your area (egg mass removal, pesticide stem injections).

Infestation Status

Over the past few seasons, LDD moth populations are rising, and they are moving into new areas across Toronto. The Ontario Ministry of Northern Development, Mines, Natural Resources and Forestry (NDMNRF) has indicated this is the worst infestation in Ontario in 30 years.

To assess the impacts that LDD moth had on trees in Toronto, and to forecast population levels of LDD moth for the 2022 season, defoliation and egg mass survey inspections were carried out in the fall and completed in November 2021. Survey results show that the LDD moth population in 2022 is forecasted to be high in parts of the City. This may result in severe defoliation of trees unless treated with an aerial spray in 2022.

2022 Aerial Spray Strategy

The City uses Integrated Pest Management including aerial spraying to reduce LDD moth populations to manageable levels. Aerial sprays have been used multiple times over the last 15 years. The last one occurred in 2020.

The City uses aerial sprays when LDD moth populations rise to levels that could have devastating effects on Toronto’s tree canopy.

Toronto Areas Being Sprayed

The spray will treat around 800 hectares of private and public land in Wards 4 (Parkdale-High Park), 6 (York Centre), 15 (Don Valley West), 16 (Don Valley East), 17 (Don Valley North), 18 (Willowdale), 19 (Beaches-East York), 20 (Scarborough Southwest), 21 (Scarborough Centre), 22 (Scarborough-Agincourt), 23 (Scarborough North), 24 (Scarborough-Guildwood), 25 (Scarborough-Rouge Park). The aerial spray blocks, along with the other control measures the City will be implementing can be seen on an interactive map.

Products Applied During Aerial Spray

Foray 48B (Btk)

Most areas will be sprayed using a product that contains Bacillus thuringiensis subspecies kurstaki (Btk), a naturally occurring bacteria found in soil. Btk is the active ingredient within the formulation registered under the trade name Foray® 48B. It has been used effectively in past aerial sprays to control LDD moth populations (2007, 2008, 2013, 2017, 2019 and 2020).

Foray 48B (Btk) is approved by Health Canada for aerial use over urban areas. It has been extensively studied by Health Canada and the US Environmental Protection Agency (EPA). Research shows that Btk poses minimal risk to human health when used as directed. It has been used by many countries over the last 30 years, including Canada and the United States.

How Foray 48B (Btk) Works

Foray 48B (Btk) works on young caterpillars, moths and butterflies (lepidopterans). Foray 48B (Btk) does not affect mature (later instar stages) caterpillars, adult moths and butterflies. Foray 48B (Btk) does not affect other insects, honeybees, fish, birds, or mammals.

Foray 48B (Btk) produces a protein that is toxic only to the larvae (caterpillars) of specific insect species. When ingested by susceptible insects, the toxic protein molecules break down the walls of the insect’s stomach causing the insect to stop feeding. The insect usually dies within two to five days.

Foray 48B (Btk) is proven to be an effective product in managing LDD moth and is also more cost effective, however, it will impact other butterfly or moth caterpillars that may be feeding at the time of the aerial spray. Since these spray areas are in mostly residential neighbourhoods, the level of biodiversity and impacts to other species is lower than in a natural area like High Park.

BoVir Use in High Park

BoVir is a pesticide containing baculovirus, Lymantria dispar Nucleopolyhedrovirus (LdMNPV), and it is highly selective to LDD moth alone. High Park is an Environmentally Significant Area (ESA) with high biodiversity and a high oak tree population that is susceptible to LDD moth defoliation.

How BoVir (LdMNPV) Works

As BoVir (LdMNPV) is a highly selective pesticide for LDD moth, it will not affect other types of caterpillars that may be feeding at the same time. BoVir will not impact other insects, mammals, birds, amphibians or other moth or butterfly species.

BoVir (LdMNPV) contains a natural occurring virus that specifically affects LDD moth caterpillars and can be very effective at naturally controlling populations. This virus does occur naturally, though it requires a cool, wet spring to be effective and it may take several seasons to naturally build up to a degree that will have an effect on LDD populations. By the time this takes place, serious damage to trees may have already occurred.

When ingested by the LDD larvae, their feeding will decease within three to four days. Once ingested, the insect is infected with the virus and usually dies within six to nine days following infection.

Foray 48B (Btk) is proven to be an effective product in managing LDD moth and is also more cost effective, however, it will impact other butterfly or moth caterpillars that may be feeding at the time of the aerial spray. Since these spray areas are in mostly residential neighbourhoods, the level of biodiversity and impacts to other species is lower than in a natural area like High Park.

Emergency Registration for BoVir (LdMNPV)

Emergency Use Registration to allow for use of BoVir (LdMNPV) in Toronto during spring 2022 has been approved by the Pest Management Regulatory Agency (PMRA) and the Ministry of Environment, Conservation and Parks (MECP). A similar product has been utilized in the USA since 1978. Over the past year the City has supported negotiations to request emergency registration of BoVir (LdMNPV), to allow for use in the period from April 1, 2022 to March 31, 2023 to address LDD Moth outbreaks in the City of Toronto in 2022.

The Ontario Ministry of Northern Development, Mines, Natural Resources and Forestry (NDMNRF) is the provincial department responsible for addressing invasive species that impact the natural environment within Ontario. NDMNRF is the sponsor for the Emergency Registration application for BoVir (LdMNPV); and Andermatt Canada Inc., the registrant for BoVir (LdMNPV).

Preparing for an Aerial Spray

No special precautions are required for residents in the spray zone. If people wish to avoid exposure, they can consider:

  • Remaining indoors during and for 30 minutes after spraying to allow for the droplets to deposit onto the tree leaves.
  • Bringing laundry, toys and pets indoors before spraying begins.
  • Practicing good personal and food hygiene (hand washing after outdoor activities, especially after gardening; leaving outdoor shoes at the door; washing all fruits and vegetables before eating or cooking).
  • Covering lawn furniture, outdoor tables, pools, barbeques, play equipment and sandboxes and/or rinsing them off with water after spraying is finished.
  • Minimizing opening and closing windows and doors during the spraying. Shutting off the heating/cooling vents or selecting the recirculate setting.
  • Contacting your family physician if you are concerned that a personal medical condition may be aggravated by the spraying.

Residents Who May Have Sensitivities

Foray 48B (Btk) and BoVir (LdMNPV) aerial spraying is not expected to have adverse effects on vulnerable populations including:

  • children with asthma
  • people with weakened immune systems
  • pregnant women
  • the elderly

Infrequently there may be some residents who are more sensitive and may experience skin, eye or respiratory irritation. If you experience an adverse reaction or worsening medical condition, speak to your physician or, in an emergency, call 9-1-1.

Individuals who have concerns should take reasonable precautions to avoid exposure during spraying.


If you live in a treatment area, bring pets indoors before the spraying begins. This will reduce pets from bringing pesticide indoors; however, Foray 48B (Btk) and BoVir (LdMNPV) are not considered a risk to pets or animals.

Patio Furniture and Barbeques

The spray does not damage paints or finishes on automobiles, houses, boats or trailers. If possible, close and cover your barbeque or bring it into a covered area, before spraying. Barbeques left open or uncovered should be rinsed with water prior to use.

If the spray residue is left to harden, it can be removed with water but may require more effort. The sooner it is washed off, the easier it is to remove.


Foray 48B (Btk) and BoVir (LdMNPV) biodegrade quickly through exposure to sunlight. If possible, cover pools during the spray period. After the spraying, remove the pool cover and consider testing the water to ensure chemistry balance prior to swimming. If the pool was not covered during the spray, test the water for chemistry balance prior to swimming.

During an Aerial Spray

Organized and coordinated by the City, the aerial spray follows provincial and federal regulations, guidelines and best practices. During an aerial spray, one helicopter with a spray system will fly about 15 to 30 metres above the tree canopy. The product is directly applied to tree foliage as the caterpillars must feed on the treated leaves for the insecticide to be effective.

Aerial Spray Schedule

The seasonal spray window is set for May 16 to June 15, 2022. On the day of the sprays, helicopters will begin spraying just before sunrise (5 a.m.) and will take approximately 2.5 hours to complete. Spraying is weather dependent and can only be started in the right conditions. Spray dates are confirmed 48 hours in advance and can be cancelled if weather conditions change.

The best time to apply Foray 48B Btk and/or BoVir (LdMNPV) is in mid-May when caterpillars are small and feeding. Applications can occur any day of the week, including weekends. Once the leaves are a certain size, the caterpillars have reached almost 90 per cent emergence and the caterpillars begin feeding, the spray window can be narrowed. Once these factors are met, weather conditions are monitored.

Pesticide application is weather-dependent. Ideal application conditions consist of:

  • Calm winds (1-16 km/h)
  • High humidity (> 40%)
  • Temperatures between 2 and 25 degrees Celsius
  • No precipitation within the spray window dates and ideally not for 24 to 48 hours after application

Postponed Aerial Sprays

Bad weather or wind may cause the aerial spray to be postponed with little advanced notice. The City will issue a communication to the public 48 hours before each treatment and provide up-to-date information through 311, online, through the City’s social media channels (Twitter and Facebook) and through Aerial Spray Email Updates. The spray may be postponed up to 24 hours in advance if the weather conditions change.

Additional Information

If you have read through this webpage and have additional questions

The City of Toronto will be conducting an aerial spray program using the pesticides Foray 48B Biological Insecticide Aqueous Suspension and BoVir Suspension Concentrate Insecticidal Virus (High Park Only) for the control of LDD Moth this spring.

Proposed spray window for application: May 16 to June 15, 2022

All spray blocks will be receiving two applications of pesticide, three to 10 days apart. Due to the physical extent of the spray areas and logistics of spraying, there may be multiple days of helicopter activity to ensure all areas receive adequate coverage. Please consult the interactive map on this webpage and click on spray block to see if that block will be receiving spray on a given day.

Specific spray dates are weather dependent and will be selected 48 hours in advance and posted on our website as well as broadcast through the City’s Facebook, Twitter and Instagram channels. Subscribers to the email notification will be notified 48 hours prior to spray dates as they become available, email notification subscription is available through this web page.

  • Method of application: Aerial spray via helicopter
  • Pest being controlled: LDD Moth (European Gypsy Moth)

Pesticides being applied

Foray 48B Biological Insecticide Aqueous Suspension

This is a registered pesticide under the Pest Control Products Act (PCP# 24977).

The active Ingredient in Foray 48B is Bacillus thuringiensis, spp. Kurstaki strain ABTS-351 (Btk).

BoVir Suspension Concentrate Insecticidal Virus (specific to High Park only)

This is a registered pesticide under the Pest Control Products Act, (PCP# 34427).

The active Ingredieant in BoVir is Lymantria dispar Nucleopolyhedrovirus, (LdMNPV).

Areas to be treated with Foray 48B

Refer to the Interactive Map to see actual spray blocks.

Ward Number Ward Name Name of Area to be sprayed within the Ward Area (ha)
6 York Centre Rockford 23
15 Don Valley West Sunnybrook Park 41
16 Don Valley East Valentine, Sagebrush, Sulkara, Deepwood, Crossburn, Laurentide, Three Valleys 78
17 Don Valley North Lescon, Mango, Beardmore 143
18 Willowdale Gwendolen Park 5
19 Beaches-East York Glen Stewart 21
20 Scarborough Southwest Fallingbrook, Kingsbury, Crescentwood 16
21 Scarborough Centre Rossander, Thompson Memorial 81
22 Scarborough-Agincourt Huntingwood 24
23 Scarborough North Stubbswood, Chartland 78
24 Scarborough-Guildwood Seven Oaks, Purpledusk 130
25 Scarborough-Rouge Park Gennela, University of Toronto Scarborough Campus 21, 18

Area to be treated with BoVir

Refer to the Interactive Map to see actual spray block.

Ward Number Ward Name Name of Area to be sprayed within the Ward Area (ha)
4 Parkdale-High Park High Park 128


For more information, virtual community meeting info, spray block maps and for actual spray dates as available:

  • Call 3-1-1. (Outside City of Toronto limits call 416 392-2489 – collect calls will be accepted)
  • Email Urban Forestry directly at foresthealthcare@toronto.ca

Two virtual information sessions about the City’s upcoming aerial sprays were held in April. If you were not able to attend, a pre-recorded presentation is available to watch.

Help manage LDD moth by following these Integrated Pest Management Strategy techniques.

Wearing long-sleeve shirts and protective equipment such as gloves and face masks or face coverings will help to minimize exposure to LDD Moth hairs, silken threads, and shed skins, which can cause skin rashes and upper respiratory tract irritation in some people.

Report an LDD Moth Sighting

Toronto residents are encouraged to report any sightings of LDD Moth through the City’s online reporting tool. The input from residents reporting the presence of this insect is important in coordinating monitoring efforts across the City.

311 can assist residents with submitting a report using the reporting tool. When calling 311, please be prepared to give the exact address of the LDD moth sighting to submit a report through the tool.

City staff will use the information collected to determine the level of the infestation in specific areas by conducting egg mass surveys during the fall and winter seasons.

August to May: Egg Mass Removal

Carefully survey your property for egg masses and scrape them off surfaces into soapy water to destroy them. In addition to trees, egg masses can be found on eaves troughs, doorframes, under patio furniture, play structures and garden stones.

Required Supplies

  • A flat object such as a butter knife or plastic paint scraper
  • Catchment container or bag to collect the egg masses
  • Bucket of soapy water. Dish soap works well

Step-by-Step Instructions

  1. Place your catchment container below the egg mass
  2. Use your scraper tool to remove the egg mass from the surface. Ensure that all eggs are scraped. Try not to leave any residual eggs in bark ridges or crevices
  3. Empty the contents of your catchment container or bag into a bucket of soapy water
  4. Leave the eggs sitting in the bucket for a day or two, then dispose of the contents in the garbage. Don’t scrape egg masses onto the ground; this does not necessarily kill the eggs and some may still hatch next spring

Egg masses can be located high up in trees. Be safe if trying to access anything up high, especially if using ladders. Some private tree care companies can be hired to provide this service at heights.


Late May to Early June

Btk Application

For severe infestations, apply a product that contains Btk to foliage at the early stage of caterpillar development when caterpillars just begin feeding. This is usually around mid-May. The pesticide must be ingested by the caterpillar to be effective.

For small trees and shrubs that you can reach, products like Safer® Brand Caterpillar Killer can be purchased at local garden supply stores.

TreeAzin Injections

For larger trees, it is recommended that you consult with a private arborist about pesticide injections.

Injections work for larger trees that can’t be sprayed from the ground or are too difficult to access. Pesticide injections are not recommended for evergreen or needle bearing trees such as spruce or pine.

Additional information about ground spraying and tree injections is available under the City’s Integrated Pest Management Strategy section of this web page.

May to July: Hand Pick Caterpillars

Handpicking caterpillars is most effective on small newly planted trees, shrubs, and plants infested with LDD moth. If possible, gently shake the tree so caterpillars fall from leaves. Thoroughly inspect the remaining foliage, branches, and trunk for caterpillars and using gloves, pick them off your tree. Fallen and collected caterpillars should be placed and left to soak in soapy water to destroy them.

May to September: Burlap Banding

Once LDD Moth caterpillars grow to about an inch (2.5 cm) in length by mid-June, they will move down the trunk to seek shelter from predators and heat. Reduce the number of caterpillars on the trees in your yard by trapping them.

Required Supplies

  • Burlap cloth
  • Twine or rope
  • Bucket of soapy water. Dish soap works well

Step-by-Step Instructions

  1. Wrap and secure a piece of burlap cloth around the stem/trunk of your tree
  2. Tie twine or rope around the center or slightly below the center of the burlap
  3. Drape the burlap cloth over the twine or rope so there is an overhang where the caterpillars can crawl underneath to seek shelter during the day
  4. Check the trap by lifting the overhanging burlap cloth every afternoon and collect any hiding caterpillars
  5. Put them into a bucket of soapy water for a few days to destroy them


Year-Round: Consult with a Professional

Consult an arborist for treatment options or contact your local garden supply store for the availability of materials.

In an ongoing effort to lead an inclusive organization, the City of Toronto is transitioning away from the use of the term gypsy moth for the insect Lymantria dispar dispar, and will be using the term LDD moth moving forward. On March 2, 2022, the Entomological Society of America adopted spongy moth as the new common name for the LDD moth. The common name of LDD moth and other moth species are currently under review internationally and within Canada, including by the Canadian Food Inspection Agency (CFIA). While some Canadian municipalities are already using this common name, for now, the City of Toronto will continue to use the scientific name Lymantria dispar dispar (LDD moth) as part of the 2022 LDD Moth Control Program and until an official common name is decided.

The LDD moth is an invasive insect from Europe that was accidentally introduced in North America in the 1860s during an attempt to rear an alternative silk-producing insect. LDD moth caterpillars are 5 to 60 millimetres in length, dark and hairy, with five pairs of blue dots and six pairs of red dots on the back. They feed on a wide range of hardwood trees, as well as evergreen trees, but show a preference to oak trees.

Extreme LDD Moth outbreaks have been associated with skin rashes and upper respiratory tract irritation in some people exposed to airborne LDD Moth hairs, silken threads, or shed skins.

There is a potential for some people to develop minor skin irritations or rashes when they come in contact with these insects. If this is a concern, it is recommended that you try and avoid contact whenever possible.

Distribution in Canada

LDD moth is established in the northeastern U.S.A. and in regions of the eastern Canadian provinces. The spread of LDD moth across North America is attributed to the movement of the insect via infested wood or hitchhiking on vehicles. Public awareness could significantly reduce and limit the spread of LDD moth to new areas.

The Early Detection and Distribution Mapping System (EDDMapS) of Ontario will display the current range of the LDD Moth.

Tree Damage

The LDD moth caterpillar is known to feed on most species hardwood trees with the exception of ash, tulip-tree, American sycamore, London plane, catalpa, fir and cedar. Most healthy trees can withstand one to several years of severe defoliation by LDD moth. Under normal circumstances, defoliated trees should regrow their leaves by the end of July, depending on the weather conditions during the season.

A spruce tree with a significant amount of brown needles.
An infested spruce tree.
The top branches of an oak tree, completely stripped of all leaves
A severely defoliated oak tree.

Oak species, particularly white oaks, and Colorado spruce are very vulnerable to LDD moth feeding and can be killed in one season when a significant proportion of the foliage is consumed. Severe loss of leaves or needles can also stress trees and make them more susceptible to further harm from other insectsdiseases and weather fluctuations. Evergreen species of trees, for example blue spruce and white pine, are particularly vulnerable once large portions of their needles are consumed by LDD caterpillars, they generally do not recover.

LDD Moth’s Natural Predators

LDD moths have three significant natural enemies:

  • a fungus (Entomophaga maimaiga)
  • a virus (Nucelopolyhedrosis)
  • a small wasp (Encyrtidae family)

The fungus and virus can be very effective at naturally controlling populations, however, they require a cool wet spring to be effective. The wasp can parasitize up to 30% of the eggs that are near the surface of an egg mass, but cannot reach the eggs in the center of the mass.

An emaciated EGM caterpillar.
Entomophaga is a fungus that infects LDD moth caterpillars. It requires a cool, wet spring.
A EGM caterpillar hangs limp from a tree.
The virus Nucelopolyhedrosis kills LDD moth caterpillars but requires a cool, wet spring.
Parasitic wasps on an EGM egg mass.
Parasitic wasps eat eggs on the outer edge of egg masses, but the inner eggs remain untouched.

A circle indicating the LDD moth's lifestyle, with shading that indicates the length of time spent in one stage. There are images of the insect at these stages, as well as text explaining them briefly. This textual information is available in full following this image.

LDD moth has four distinct developmental stages:

  1. egg
  2. caterpillar
  3. cocoon
  4. moth


  • Late August to early May
  • Stage lasts eight months
  • Dormant, over-wintering stage

Egg masses remain secured to surfaces such as tree bark, outdoor furniture, landscape stones and vehicles and hatch to coincide with the warm weather and the opening of tree buds. Egg masses range in size from 2-8 cm long and can contain between 100-1000 eggs.

Clumps of egg masses on a tree.
An egg mass on a tree.


  • Early May to mid-July
  • Stage lasts 40 days
  • Tree-damaging stage

Newly hatched caterpillars are about half a centimetre long and dark in colour. The tiny caterpillars begin the climb up to the tree canopy, though if it is rainy they may stay put for several days. The caterpillar will either begin to feed on the newly flushed leaves or travel to a nearby tree though a method called “ballooning”, where they dangle from long silken threads at the end of branches and are carried away by the breeze. While their light bodies can travel several kilometres, they will typically be carried to the tree right next to them.

LDD moth caterpillars grow and change in appearance over the span of one to two months. As they grow, they moult or shed their skin. By the fourth moult, the pairs of characteristic blue and red dots are visible on their back.

A single caterpillar can eat an average of one square meter of foliage. They continue to feed, moult, and feed until they are about six to seven centimetres long. Once they’ve finished feeding, they seek shelter to cocoon.

Small caterpillars, newly hatched, on a tree.
Newly hatched LDD moth caterpillars.
An older caterpillar showing characteristic spots, resting on a severely defoliated leaf
An older caterpillar, showing characteristic spots, eating a leaf.


  • Mid-July to early August
  • Stage lasts 10 to 14 days
  • Transformation stage

After the adult moth emerges, it leaves the empty cocoon behind. The female cocoon is larger than the male cocoon.

A gypsy moth cocoon against a severely damaged leaf.
The LDD moth cocoon stage.


  • Late July to mid and late August
  • Stage lasts 10 days
  • Reproductive stage

An adult LDD moth’s only function is to reproduce. Unlike other species of butterflies and moths, adult LDD moths do not eat anything. The female is larger than the male and is cream coloured. The female moths cannot fly. Instead, she uses pheromones to attract male moths. Male moths are smaller and brown in colour.

A brown male moth is smaller than the cream-coloured female.
Adult male, bottom left, and adult female, upper right.


LDD moth outbreaks may appear suddenly and may continue for two to five years in any one location. Natural control factors such as disease, parasites and predators eventually combine to cause a collapse of these outbreaks. Consecutive years of LDD moth at outbreak levels can cause severe defoliation which can lead to tree mortality and intervention may be required.

The LDD moth management program aims to control outbreak levels of LDD moth in areas with trees that are potentially at risk of severe defoliation or mortality if no action is taken. Eradication of LDD moth is not a realistic management objective since it is well established throughout North America.

To help manage infestations, the City will continue to use the Integrated Pest Management (IPM) Strategy. IPM is a sustainable approach to managing pests by combining biological, cultural, physical and chemical controls in a way that minimizes economic, health and environmental risks.

IPM aims to suppress pest populations to an acceptable level or threshold.

Fall and Winter

LDD Moth Egg Mass Surveys

City staff conduct egg mass surveys in residential neighbourhoods, parks and natural areas to identify areas infested with LDD moth. Surveys are typically conducted in parts of the city with historic LDD moth infestations and in new areas where residents have reported LDD moth sightings. These surveys allow City staff to delineate the infested areas and to forecast LDD moth population levels for the following spring. City tree(s) with high numbers of egg masses that are at risk of being defoliated are candidates for treatment.

Winter and Spring

The City will prescribe different types of treatments depending on the infestation level, tree species, size of the tree, and its location. Each treatment has limitations, so a combination of control measures is essential for a successful control program. Treatments are to reduce the LDD moth’s population levels and to prevent severe canopy damage from occurring and tree mortality.

Egg mass removal

The physical removal of egg masses is an effective method of control for small to medium-sized, low-risk tree species, such as Norway maple, linden and honey locust, located on residential streets or City parks. City staff are equipped with vacuums attached to extension poles that are used to remove and collect the egg masses off of the tree. Egg masses collected this way are destroyed off-site to ensure they no longer pose a threat.

A worker on the ground holds a long tube to a high tree branch
Vacuuming egg masses from a high branch.

TreeAzin Injections

TreeAzin is a botanical injectable pesticide formulated with an extract of neem tree seeds that provides a treated tree with protection from LDD moth feeding for one season. When a caterpillar eats the leaves of a treated tree, the pesticide kills the insect by preventing it from growing any larger. This limits the amount of damage to the tree. High-risk trees – trees that are predicted to be severely defoliated – are generally selected for this treatment. The timing of treatments is essential for successful control.

The base of a tree has a number of white cylinders sticking out of it
TreeAzin injection capsules sticking out of the base of a tree.

Ground Sprays of Btk

The City uses products that contain the active ingredient Bacillus thuringiensis subspecies kurstaki (Btk). This is a naturally occurring bacteria found in soil that can be sprayed onto the foliage of individual trees for LDD moth control. Ground spraying for LDD moth is a control often used in City parks to treat spruce trees since other methods have proven to be unsuccessful. The timing of these applications is extremely time sensitive as there is a very narrow treatment window for Btk applications. Because of this, the number of trees selected for this method of treatment is limited.

A worker sprays a long jet of pesticide into a tree
City staff applying a ground spray to a tree.

Aerial Spray Program

The City plans aerial spray programs when LDD moth outbreaks are severe and widespread across large areas of dense high-risk tree canopies, usually oak-dominated. Aerial sprays are only conducted when there is no other Integrated Pest Management control option available that would reduce the populations significantly enough to meet acceptable thresholds.

Early Summer

Post-treatment defoliation surveys

During the months following the treatments, City staff conduct post-treatment monitoring surveys to assess the level of feeding on treated trees/areas. Treated trees are inspected for signs and levels of feeding activity and caterpillar abundance. These areas are later re-inspected in the fall/winter to assess for egg masses that were laid during the late summer. The goal of the treatment program is to protect individual or groups of trees from damaging levels of defoliation and to reduce LDD moth population levels. Low to moderate levels of feeding – small holes in leaves – and the presence of caterpillars can still be expected following treatments as it is impossible to completely eliminate the insect.

Late Summer

Pheromone trapping

The City deploys LDD moth traps across parts of the City where LDD moth is present. Though they are commercially marketed as a control method for this insect, these traps are a population monitoring tool, not a control measure. The traps are baited with a sex pheromone that is effective in attracting male moths. Traps are hung in the lower canopy of trees in the summer, before the expected flight period in late July through August. Once the moths have died off for the season, the traps are collected and the number of moths counted. The data collected from these traps is used to establish further monitoring and treatment efforts.

A pheromone trap hangs in a tree. It has a white base and a green lid.
An LDD moth pheromone trap hanging in a tree.


Parasitism surveys

Parasitism is one of the greatest factors that contribute to the natural collapse of LDD moth populations. Since LDD moth has natural enemies that affect the insect at each stage of development, City staff monitor the level of parasitism throughout its life cycle. City staff monitor the location, prevalence and severity of parasitism in areas of the city to help predict LDD moth population levels the following spring.