Formerly known as LDD Moth - Lymantria dispar dispar
Help Protect Markham's Urban Forest
Spongy Moth, formerly known as LDD Moth (Lymantria
dispar dispar), is a non-native, invasive forest pest that was introduced to North America from Europe in 1869. It was first detected in Ontario in 1969 and has quickly spread across southern Ontario during the 1980’s. Spongy Moth is considered a well-established regional pest in southern Ontario and is known to have cyclical outbreaks every 7 to 10 years.
Although complete eradication of the Spongy Moth is impossible, the City is taking an Integrated Pest Management (IPM) approach to help reduce the Spongy Moth egg mass count and limit the Spongy Moth caterpillar damage, thus helping protect our Markham trees and green infrastructure. This means we are using different management techniques to address the pest population starting with the least harmful to the environment.
The caterpillars tend to feed on the leaves of select hardwood tree species (mainly Oak, Birch and Maple) between the months of early May and mid-July. In rare cases, when their population size is extremely high, the caterpillar will feed on evergreens such as Pine and Spruce.
The diagram below indicates various control methods which can be utilized throughout the season.
Eggs are fuzzy in texture, and a cream-brown colour, approximately 2 to 3 centimetres wide. They are commonly found in tree bark crevices, as well as on vehicles, garbage cans, house brick siding and even outdoor furniture. The insect spends the Winter in the egg stage and then hatches the following Spring.
Caterpillars hatch end of April to early May. Caterpillars will be very small at first and will grow to approximately 2.5 centimetres in length. During the day, they will begin moving down the tree to hide from the hot sun and will climb back up late afternoon to feed on tree leaves at night. Caterpillars are dark in colour, with noticeable red dots along their back. The caterpillars will be covered in dark hairs. The caterpillar stage will last for approximately 40 days, before pupating.
Late June to early July, the caterpillar will begin to seek shelter to pupate. This stage will last for approximately 10 to 14 days. The caterpillar will form a dark brown cocoon-like structure, in which it will undergo transformation into the adult moth.
Moths are light brown to white in colour. They do not feed on tree leaves in this stage. Instead they will have 2 weeks to mate and reproduce before they die. Each female moth will lay between 500 to 1,000 eggs. The female cannot fly and tends to stay on the tree that she pupated on. Only males can fly.
Between the Fall of 2021 and the Spring of 2022, City staff removed egg masses from approximately 28,000 City trees along boulevards and within parks. Egg masses were removed from the first 15 feet of each tree. It is not feasible to remove all egg masses from all trees and any remaining egg masses on trees that staff have visited mean they were not safely within reach of the equipment used to remove the egg masses.
Spongy Moth is well established on both City and private trees making it impossible to remove every egg mass completely. While complete eradication is not possible, our overall objective is to reduce the Spongy Moth population and reduce the damage to our green infrastructure.
Aerial spraying was not deemed necessary in Markham. Aerial sprays do not reduce spongy moth populations over the landscape in the long term, especially when their presence is widespread and infestation levels are at their peak. They are also non-selective and can impact non-target caterpillars, who are an important source of food for many birds, pollinators and other wildlife.
Since aerial sprays require two applications within a very narrow timeframe which need to occur right after the caterpillars emerge and requires specific weather conditions, they are logistically complex. Due to the negative public perception associated with aerial sprays of pesticides, some homeowners/landowners and environmental groups may oppose aerial spraying of Bt.K.
During severe infestation, an insecticide or biological control such as Bt.K may be considered as a viable option.
Homeowners can consider consulting with, and hiring a licensed arborist or contractor to apply sprays or tree injections. Timing of the application and the treatment of the entire canopy is essential to the success of control.
Spray applications do not produce an instant defense and will not completely eradicate the problem, but it can be very effective in reducing the insect population when used appropriately. Limiting factors to consider when using a spray application can include the current season and lifecycle of the pest, timing of the day, weather conditions and patterns as these products need time to dry on the trees' foliage and in some cases, such as Bt.K, will require multiple applications for the desired level of control.
Property owners are responsible for managing trees (and pests) on their property. There are several pest management options to consider and to control the impacts of Spongy Moth.
- August to April
Scrape egg masses off of trees and place in a bucket or zip lock bag of soapy water for a day or two before disposing of them.
Removing egg masses reduces the number of hatched caterpillars in the Spring.
If any eggs fall on the ground, be sure to collect these in soapy water as well, as egg masses left on the forest floor or turf, will still hatch in the Spring.
Be sure to wear some hand protection, as the hairs of the Spongy Moth caterpillar have been known to cause mild skin irritation in some individuals.
Watch the City of Markham video below.
— April to June
Wrap your trees with burlap banding to trap Spongy Moth caterpillars. Check the burlap cloth every afternoon to collect caterpillars that may be hiding. Place caterpillars in a bucket soapy water for 48 hours before disposing of them.
If trees are severely infested, an insecticide may be a viable option. Contact a professional and licensed tree care company to discuss the best options.
— June to August
Similar to trapping the caterpillars with burlap, burlap banding can also be used for female moths (which are unable to fly). Wrap burlap lower on the tree trunk to trap the female moth before it crawls up the tree to lay her eggs. Wear gloves and place the moths in a bucket of soapy water for 48 hours before disposing of them.
Leave burlap and twine on the tree until the end of August, then remove. Burlap and twine can be reused next year, or be sure to dispose of these materials in the garbage so it does not become litter.
Water your private and boulevard trees. This will provide the energy for your trees to continue to grow. Many trees will grow new leaves later in the Summer months, even after being defoliated.
The City of Markham is using an Integrated Pest Management (IPM) strategy in conjunction with the Region of York and industry experts. IPM is a sustainable approach to managing pests that combines biological, cultural and physical factors to control in a way that targets a specific pest and minimizes impacts to others.
The following integrated pest management strategies are currently being used:
Scraping and Removal
During the Fall of 2021 and the Winter of 2022, the City of Markham staff manually removed Spongy Moth egg masses from approximately 28,000 street & park trees. Staff visited every street within the City of Markham.
During the Spring of 2022, approximately 150 select high-value street and park Oak trees will be treated using an injectable biological insecticide called TreeAzin™. TreeAzin™ is made from the seeds of the Neem tree and when injected, the insecticide will kill the caterpillar by preventing it from growing any larger. The caterpillar must ingest part of the trees leaves (which will contain the insecticide) in order for it to be successful. Many municipalities, including Markham, have used TreeAzin™ in the past for the treatment and control of the Emerald Ash Borer (EAB) invasive species. Additional information on TreeAzin™ can be found at: https://bioforest.ca/en/canada/product-details/treeazin-systemic-insecticide/
Banding Trap Kits
During the Spring of 2022, several events were held to provide distribution of pre-assembled burlap banding kits. Approximately 4,000 kits have been provided to City of Markham residents for use on their privately-owned trees.
and Data Collection
City of Markham staff continue to document neighbourhoods of ‘heavy’ to ‘severe’ defoliation impacts, to better plan for future strategies. Information collected and shared by neighbouring municipalities offer a variety of educational tools and resources.
Surveys and Further Studies
In July 2022, the Region of York will be conducting defoliation surveys on previously-surveyed plots to look at the actual defoliation levels (which the egg mass surveys in 2021 attempted to predict), and look for signs of the nucleopolyhedrosis virus (NPV). Actual defoliation versus predicted defoliation helps confirm the accuracy of the egg mass surveys and signs of NPV can be an indicator that the Spongy Moth population is declining.
In late fall/early Winter 2022, the Region of York will be re-surveying the plots for egg masses to help with 2023 Spongy Moth predictions and planning.
Various naturally occurring methods exist in reducing Spongy Moth populations. These natural “enemies” of the Spongy Moth have been proven to contribute to the eventual collapse of Spongy Moth populations.
Virus (NPV) – a naturally occurring virus
Usually the most important factor in the collapse of Spongy Moth outbreaks in North America. The virus is always present in a Spongy Moth population and can be transmitted from the female moth to her offspring. It spreads naturally through the Spongy Moth population especially when the population builds to high levels. Caterpillars are more susceptible to this virus because they are stressed from competing with one another for food and space. Typically, 1 to 2 years after an outbreak begins, the NPV virus causes a major die-off of caterpillars.
Entomophaga maimaiga – a
naturally occurring fungus
Fungal spores that overwinter in the soil will infect young caterpillars early in the Summer. When the young caterpillars die, their bodies produce windblown spores that can spread and infect older caterpillars. Within several days, the cadavers fall to the soil and disintegrate, releasing the spores that will overwinter back into the soil. The fungus is most effective at reducing caterpillar populations, during cooler and wet seasons.
Evidence suggests, that egg masses exposed to prolonged periods of extreme cold weather (below -20 degrees Celsius, for more than 2 days) may die off. Egg masses must be exposed to winter conditions, such as on the outside of tree bark edges, while egg masses laid in crevices or at tree bases, may be insulated from the extreme weather.
Some birds, mammals and rodents will also feed on the growing larvae – but this type of predation is unlikely to cause a population decline.
During severe outbreaks, trees can be completely defoliated. The tree may produce a new set of leaves but may also store the energy to set buds for next year’s leaves. It is unlikely that the tree is dead. Even if all of the leaves are gone it is important to water the trees on your property to provide them with the energy to grow new leaves.
In July 2021, for example, trees which had been completely defoliated have already grown a complete set of new leaves.
Yes and no. Provided the tree is relatively healthy it will have new growth at the outer tips of the branches where new growth appears every year. The needles on the inner branches will not grow back and as a result it will take many years before the tree is aesthetically appealing.
Most conifers which have experienced this degree of defoliation are considered a loss and may need to be removed and replaced.