Why is an aerial spray necessary?

    LDD caterpillars eating tree leaves

    On February 16, 2022, Council passed a by-law (BL0029-2022) to declare the LDD infestation in Mississauga a matter of public nuisance. The by-law authorizes the Parks, Forestry and Environment division to implement an aerial spray program using Bacillus thuringiensis subspecies kurstaki (Btk) to control LDD within treatment areas identified by the Commissioner of Community Services.

    If left unmanaged, elevated populations of LDD will lead to significant defoliation of the City’s tree canopy. This can cause certain trees to become more susceptible to disease and extreme weather events like drought and ice storms.

    The most efficient way to treat widespread LDD populations is to apply an organic pesticide from the air. While the aerial spray will not eradicate LDD population levels. It will reduce populations to more manageable level and help protect the City's urban forest.

    Low-flying helicopters will target the spray to the tops of trees so that the spray is applied to tree leaves.

    After the spray, the City will continue to monitor LDD population levels and treatment methods for effectiveness.

    ➡️ Learn more about LDD


    What is being sprayed and is it safe?

    helicopter spraying Btk on top of some treesAccording to Health Canada, Btk treatment is considered low-risk to human health and the environment. Btk is only toxic in the caterpillar stage of the LDD life cycle and does not affect adult moths or butterflies.

    Btk works by producing a protein that is only toxic to caterpillars of specific insect species like LDD. When ingested by an LDD caterpillar, the toxic protein molecules break down the walls of its stomach causing it to stop feeding and die.

    The City will be using a product called Foray® 48B Biological Insecticide, Aqueous Suspension, which contains the active ingredient Btk. It is registered under the Pest Control Product Act (registration #24977) and is approved by Health Canada for use in urban areas. This has been used effectively in all past aerial sprays in Mississauga to control for LDD (2006, 2007, 2018).

    ➡️ View the material safety data sheet for BTK formulation Foray® 48B

    ➡️ Residents with any concerns or questions about health and the use of Btk can call Peel Public Health at 905-799-7700 or speak to their family doctor.


    How do I prepare?

    The City is committed to ensuring all possible steps are taken to keep Mississauga healthy and habitable for all residents. The safety and health of residents and the protection of the environment are top priorities. The public may hear helicopter noises during the early morning. All necessary safety precautions are taken to ensure minimal risk to the public, staff and the applicators.

    Most residents are unlikely to experience any symptoms if exposed. A small percentage of sensitive residents may experience skin, eye, or respiratory irritation. To minimize exposure, Peel Public Health recommends that residents stay indoors during the spray and for 30 minutes following the spray to allow the droplets to settle.

    Additional actions residents can take:

    Before the spray:

    • close windows
    • turn off fans or air conditioners, or select the recirculate setting
    • bring in laundry and toys
    • cover all vegetable and herb gardens
    • keep pets indoors
    • cover pools, BBQs, play equipment, lawn furniture, and automobiles


    After the spray:

    • wash/rinse pool covers BBQs, play equipment, lawn furniture and automobiles with water
    • Practice good personal and food hygiene (e.g. hand washing after outdoor activities, especially after gardening; leave outdoor shoes at the door; washing all fruits and vegetables before eating or cooking)
    • wash pets’ paws before entering the home

    ➡️ Residents with any concerns or questions about health and the use of Btk can call Peel Public Health at 905-799-7700 or speak to their family doctor.


    Can LDD affect my health directly?

    It is recommended that residents avoid exposure to LDD caterpillars. Children should be discouraged from playing with any LDD caterpillars. The spiny hairs on the caterpillars can cause welts or a patchy rash that can persist for four to five days. Residents experiencing symptoms are advised to contact a heath care professional for advice.


    What is aerial spraying?

    Aerial spraying involves spraying an area of tree canopy a compound containing a substance called Bacillus thuringiensis subspecies kurstaki (Btk), (Btk) from the air using a double engine helicopter. When employed, this work is completed by a contractor working for the city.


    What if a property lies outside of the spray area?

    The City’s spray zones encompass the areas predicted to have the greatest risk to tree health from defoliation cased by LDD in 2022. They were derived from detailed LDD monitoring data collected by the city’s consultants in the fall of 2021. There will still be LDD present elsewhere in the city. Outside of the spray areas the city will also be undertaking other measures such as egg mass scraping and ground-based treatments to help reduce impacts on the urban forest and to help residents preserve and protect tree health. Materials and information will also be provided for residents in affected areas to help combat LDD on their properties. The City’s website mississauga.ca/LDD contains tools and resources for landowners on what they can do on their own properties to combat LDD including pest control techniques and a reporting form to submit observations of LDD.


    Is the City doing anything in addition to aerial spraying?

    The aerial spray treatment is one component of the City’s Integrated Pest Management program to address LDD. Where spraying is not advantageous, ground based treatments including egg mass scraping, tree injections and/or ground sprays may be used to control localized LDD infestations on City trees.


    Is Btk safe for humans?

    Btk is an effective pesticide that has been shown to successfully manage LDD populations. 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.


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