Gardens & Trees
Invasive Species
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Invasive species damage our forests, property, and the environment. Identify invasive species on your property and learn what you can do to stop the spread!
Learn about how you can stop the spread of
Invasive Species
Commitment to Inclusion As part of the City of Hamilton’s commitment to diversity and inclusion, the City has replaced the name gypsy moth with its Latin name, Lymantria dispar dispar (LDD) in it’s communications to help educate residents about the invasive pest while remaining sensitive to the negative connotations associated with its common name.
Lymantria Dispar Dispar (LDD Moth) is an invasive forest pest that was introduced accidentally in the United States in 1869. Since then, the LDD moth has expanded its range over much of the eastern United States and Canada. It was first detected in Ontario in 1969 and has quickly spread across southern Ontario. It is now well established throughout southern Ontario and as far north as Sault Ste. Marie.
LDD moth larvae or caterpillars will feed on tree leaves. If the larvae population is high, they can defoliate whole trees and forests in a short amount of time. LDD moth prefer oak trees, but will feed on a variety of hardwood tree species. Under normal circumstances, defoliation caused by LDD moth won’t kill a tree. However, trees can decline to the point of death in some cases when defoliation is coupled with dry hot summers or impacted by other forest pests like Spring or Fall Cankerworm.
Late instar LDD moth larva
Female LDD moth laying eggs
Pupation occurs in a cocoon which can be found on a variety of surfaces including trees, rocks, houses, boats, trailers, fences, picnic tables, and firewood. In 13 to 17 days, the moths emerge. Both sexes have wings, but only the males can fly. The male moth is dark brown to beige, medium-sized, and is a very erratic flyer. The female is mostly white and has a wingspan between 60 to 70 mm. The female lays eggs in masses of 100 to 1000 on tree trunks, branches, houses, fences, etc. as well as under rocks and forest floor debris. The eggs are covered with fine brown hairs from the female’s abdomen. The egg masses will remain all winter and caterpillars will hatch in the spring, from late April to mid-May.
How The City is controlling LDD moths
In the fall of 2022, after the spring aerial treatment program, egg mass surveys were conducted City wide. The surveys indicated that overall, there are low levels of LDD infestation. The surveys also indicated that there are some persistent pockets of higher infestation. The areas of higher infestation are:
- Dundas (Dundas Driving Park, Fisher’s Mill Park)
- Ancaster (Ancaster Community Park)
- Hamilton (Woodland Cemetery).
A localized treatment program will be completed in 2023 in the areas that were determined to have higher infestations. The treatment program will include ground spraying with Btk, egg mass scraping and tree banding.
Bacillus thuringiensis ‘kurstaki’ (Btk), is a soil-borne bacterium that is applied to the leaves of affected trees while caterpillars are in their early instar stage (immature). Within 24-48 hours of ingesting Btk, the bacterium disrupts the caterpillars’ digestive system causing the caterpillars to stop eating. Caterpillars that have ingested Btk will succumb to its effects in just a few days.
Sunlight and fungi deteriorate Btk within 1 to 4 days. This means that Btk has very low residual qualities in the natural environment.
Btk requires an alkaline environment in the gut in order to be effective. This means that it does not have any detrimental effects to humans, birds, or bees. Btk can affect other caterpillar species (known as non-target species). But due to its low residual life and the narrow spray window, the non-target impact is expected to be quite low.
The City uses a conservative and measured application strategy, with the goal of reducing the population below the 2,500 egg masses per hectare. This program is not intended to eradicate LDD entirely.
Members of the public are unlikely to experience any symptoms if inadvertently exposed to Btk spray, and no special precautions are necessary. If you are concerned, you should take reasonable precautions to avoid exposure. During applications of Btk you can avoid exposure using the same strategies you would use to avoid pollen or other airborne materials during days when air quality advisories are issued. You can also avoid exposure by staying indoors with windows and doors shut during the spray period, although this action is not required by health officials. (Health Canada, 2009)
To learn more about Btk see the Health Canada Btk Fact Sheet.
LDD Moth Treatment Area
Individual trees that will be included in the ground spray program are outlined below. They are surrounded by the orange highlighted boundary indicating a hotspot zone. These hotspot zone represents where LDD moth populations are slightly higher than the rest of the city. To find out if you live in a hotspot zone, enter your address or nearby intersection into the search box.
The ground sprays will happen between May 25 and June 9. A follow up egg mass survey will be completed in Fall 2023 to assess the LDD moth population.
What homeowners can do to control LDD moths
Homeowners are encouraged to monitor their hardwood trees like oaks, maples, beech and walnut for the presence of larvae.
Handpicking caterpillars is still one of the most effective ways to help control LDD moths on small newly planted trees, shrubs, and plants. If possible, you can also gently shake the tree, so caterpillars fall from the 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.
What to look for - The caterpillars of LDD moths are dark and hairy. They have five blue dot pairs and six red dot pairs on their back. They go through 4-5 "molting" events where they shed their skin and each time, they get bigger.
You can apply a product that contains BTK (Bacillus Thuringiensis “kurstaki”) 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.
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 larvae on the trees in your yard by trapping them.
Step-by-Step Instructions
- Wrap and secure a piece of burlap cloth around the stem/trunk of your tree
- Tie twine or rope around the center or slightly below the center of the burlap
- 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
- Check the trap by lifting the overhanging burlap cloth every afternoon and collect any hiding caterpillars
- Put them into a bucket of soapy water for 2-3 days to destroy them
Step-by-Step Instructions
- You can purchase the traps at various retail stores or online throughout your area
- Put the traps out when the moths are active after coming out of their pupa stage of growth. Only male moths are attracted to the traps.
- Homemade traps can be created with various designs found on websites. The traps have a bait inside their lid that smells like female LDD moth pheromone for attracting males.
- Once captured, put the moths in a container of soapy water and leave them for 2-3 days, then dispose of the contents.
Survey your property for egg masses and scrape them off surfaces into soapy water to destroy them.
Step-by-Step Instructions
- Place your catchment container below the egg mass
- 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.
- Empty the contents of your catchment container or bag into a bucket of soapy water
- Leave the eggs sitting in the bucket for 2-3 days, then dispose of the contents.
Egg masses can be located high up in trees. Care needs to be taken if trying to access anything aloft, especially if using ladders. Some private tree care companies can be hired to provide this service at heights.
Frequently Asked Questions
LDD moth caterpillars prefer the leaves of deciduous hardwood trees like maple, elm and oak. It will also feed on apple, alder, birch, poplar and willow trees. As the caterpillar matures, and population levels increase, it will also begin to attack evergreens such as pine and spruce. LDD moth caterpillars don't appear to like ashes, sycamores, butternuts, black walnuts and dogwoods.
Tree damage depends on the degree of infestation, past defoliations, the tree's vulnerability and the environment and can range from light to almost complete defoliation. If the tree has been weakened or stressed by other conditions, and attacked repeatedly in recent years, the defoliation can result in the death of the tree.
Yes. Predators include other insects like wasps, flies, beetles, ants and spiders as well as birds such as chickadees, blue jays, robins and nuthatches. Animals such as chipmunks, squirrels and raccoons will also prey on the caterpillar.
The wasp that targets the LDD moth is a parasite of the egg. It is now commonly found wherever LDD moths are and has become an important natural control.
Also, LDD moth is susceptible to several naturally occurring diseases caused by bacteria, fungi and a virus. The virus and bacteria escalate when populations peak. The LDD moth virus disease is often referred to as “wilt” because dead caterpillars hang in an inverted “V” from tree trunks or foliage.
These natural biological controls contribute the most to keeping levels within a normal range and tend to follow 2-3 years after the moth populations peak.
Property owners are responsible for managing trees (and pests) on their property. You are encouraged to monitor trees on your property - look for egg masses in winter, caterpillars in spring, and moths in July and August - and take action to remove LDD moths as often as possible.
During severe infestation an insecticide may be considered a viable option. Homeowners can consider consulting with, and hiring a licensed contractor to apply pesticide sprays or tree injections. Timing of the application and the treatment of the entire canopy is essential to the success of control. You should also be aware that pesticide applications do not produce an instant defense and will not completely eradicate the problem, but can be very effective in reducing the insect population when used appropriately.
Our arborists have worked to remove the egg masses from City trees to reduce the population. It is not possible to eliminate this pest completely as it is well established in our region. Our overall objective is to reduce numbers. We continue to monitor numbers and will take further action if deemed necessary.
The hairs of the LDD moth caterpillars contain histamine which some people are allergic to. Not everyone will have a reaction if coming in contact with the caterpillar, but it is possible and is a known adverse effect. If you are experiencing any sort of reaction, please contact your family care physician for medical advice.
Hemlock Woolly Adelgid - Adelges Tsugae (HWA) is a destructive aphid-like pest of eastern hemlock, an ecologically significant tree species in eastern Canada. It feeds on the base of the needles, causing needle drop and tree mortality in as few as 4 years. HWA can be identified by its egg sacs, which look like cotton balls or clumps of snow, and can be found at the base of needles.
HWA was identified in Grafton, 200 km north of Hamilton in August 2022.
What to do if you think you have identified a Hemlock Woolly Adelgid population?
If you believe you have identified HWA on your property contact your local Canadian Food Inspection Agency (CFIA) Office at 905-572-2201 to have an official identification. You can also report a potential invasive pest on the CFIA website.
If you have identified a potential HWA population on a street tree or a tree within a City of Hamilton Park or Cemetery, please call the City of Hamilton Contact Center at 905-546-2489.
Photo credit: Natural Resource Canada; CFIA
For more information on Hemlock Woolly Adelgid visit Invasive Species Centre
The spotted lanternfly is an invasive insect that can destroy fruit crops and poses a threat to Canadian wine, fruit and forestry industries. Adults are present from July to December.
As early as September, adults start laying1 inch long (2.54 cm), muddy-looking egg masses on smooth surfaces outdoors (e.g. plants, bricks, stones, lawn furniture, etc.).
The spotted lanternfly was identified in Buffalo, New York near the Canadian border in September 2022.
What to do if you think you have identified the spotted lanternfly?
If you believe you have found the spotted lanternfly or its egg masses, seal them in a container and immediately notify the local Canadian Food Inspection Agency (CFIA) Office at 905-572-2201 to have an official identification. You can also report a potential invasive pest on the CFIA website.
If you have identified a potential Spotted Lanternfly on a street tree or a tree within a City of Hamilton Park or Cemetery, please call the City of Hamilton Contact Center at 905-546-2489.
Photo credit: CFIA
For more information on Hemlock Woolly Adelgid visit Invasive Species Centre
Oak wilt is a disease caused by the fungus Bretziella fagacearum that can kill an Oak tree in a single season. The fungus kills the tree by developing on the outer sapwood of the tree causing it to form growths and gums that block movement of water and nutrients. Oak wilt can be spread through roots, insects and movement of infected material (e.g., firewood).
Oak wilt is not currently present in Canada but occurs in 24 states near Ontario. Most recently, oak wilt has been detected 500 m from the Canadian border near Windsor.
Photo credits: CFIA, Arborjet, and USDA Forest Service
Signs and symptoms of Oak Wilt
- Browning or bronzing leaves beginning at the tip and moving back towards the stem, with clear border between brown and green tissue.
- Leaves near the crown of the tree changing colour.
- Early leaf drop.
- Cracks in the bark.
- Grey or tan mats of fungus under the bark of infected or dying trees.
- Sweet smell coming from the tree bark.
How you can help
- Don’t Move Firewood! Buy where you burn it or buy certified heat-treated firewood. Check with parks or campgrounds before you go for rules about firewood.
- Refrain from cutting, pruning, harvesting or injuring oak trees on your property between April 1 and July 31.
- Learn to identify oak trees on your property and become familiar with signs and symptoms.
- Follow our reporting guidelines listed below.
What to do if you think you have identified oak wilt disease?
Reports can be made by phone to the local Canadian Food Inspection Agency (CFIA) office at 905-572-2201 or to [email protected].
If you have potentially identified oak wilt on a street tree or a tree within a City of Hamilton Park or Cemetery, please call the City of Hamilton Contact Center at 905-546-2489.
Date modified
May 25, 2023