Norfolk County maintains planted and naturalized areas through best management practices such as forest thinning, invasive species control, and controlling invasive plant species. These practices create healthy forests that provide many environmental benefits. Learn about forest management operations that are happening in Norfolk County in 2021.

Invasive Species Control

Gypsy Moth Control—May 2021

Norfolk County will be conducting an aerial spray on select Norfolk County-owned woodlots within the former townships of Charlotteville and Windham for the purpose of reducing damage caused by gypsy moth.  A total of 141 acres are being treated.

Update: 05/06/2021

Gypsy moth caterpillars have started to hatch and are expected to be fully hatched by next week (May 9-15). Leaf development on the oak is still behind compared to most of the early species (poplar, maple, birch).  In order to spray we need there to be at least 60% leaf development on the oak species. Aerial application of the Btk will be waiting on the leaf development of the oak trees. We are expecting the first application to take place after May 20, 2021.

What is the European gypsy moth?

Gypsy moth (Lymantria dispar) is an invasive insect from Europe and Asia that established in North America in the late 1800s. Gypsy moth caterpillars feed on a wide range of deciduous and conifer trees but show a preference for oak species.


How much damage can gypsy moth cause to trees?

The damage done to a tree by gypsy moth depends on the degree of the infestation, past defoliation, the tree’s vulnerability, and the environment.

In a light infestation, defoliation may not be noticeable, while in a heavy infestation a tree may be completely stripped of its foliage. High levels of gypsy moth caterpillars can cause trees to experience severe loss of leaves, which may cause them to enter a state of decline and make them more susceptible to further harm from other insects, diseases, and weather fluctuations such as drought.


Why is the County planning an aerial spray?

Norfolk County has been faced with a building gypsy moth population since approximately 2017 which has resulted in repeated defoliation to host tree species – particularly oak trees.

A number of areas within Norfolk County are expected to experience a high gypsy moth population and severe defoliation during the 2021 growing season. The County will be conducting aerial spraying of select County-owned woodlots to help reduce the impact and damage caused by gypsy moth.


What pesticide is being used?

The County will be using a product that contains Bacillus thuringiensis ‘kurstaki’ (Btk). The product is registered under the trade name Foray® 48B (Pest Control Products Act #24977). This is the same product that was used successfully in Norfolk County during the previous infestation event of 2008.

Btk is a soil-borne bacteria that is applied to the leaves of trees while caterpillars are in their stages of development. Once ingested, it disrupts the caterpillar’s digestive system and within a couple of days, the caterpillars will stop eating and succumb to its effects. Btk has very low residual qualities in the natural environment since ultraviolet light and rain deteriorate and wash away the bio-pesticide within 1 to 4 days. Btk requires an alkaline environment in the gut to be effective, so it does not affect other insects, fish, birds, or mammals. Btk will affect other caterpillar species; however, due to its low residual qualities and the timing of the spray, the impact on non-target species is greatly reduced.



Preparing for an Aerial Spray

Residents are unlikely to experience any adverse health effects from exposure to Btk, and no special precautions are necessary or required. However, if you live adjacent to one of the woodlots being treated and you have concerns about exposure, you may take reasonable precautions such as:

    • Remaining indoors for 30 minutes after spraying to allow the droplets to settle on tree leaves
    • Bringing laundry, toys, and pets indoors before spraying starts
    • Practicing good personal hygiene such as washing hands after outdoor activities
    • Covering pools and outdoor furniture, BBQs, etc, and rinsing them off with water after spraying
    • Keeping windows and doors closed during the spraying
    • Disconnecting any roof collecting cisterns

Norfolk County has considered the proposed spray locations in relation to adjacent private land uses. Where proposed spray locations are adjacent to residential areas, the residential area has been buffered by approximately 100 meters, meaning no spraying will occur within 100 meters of a residence.

Access to County-owned woodlots being treated will be restricted during application operations.



Follow-up activities

Later in the summer, after the spray has been completed, County staff will conduct post-treatment monitoring surveys in order to determine the overall success of the spray. Eggs mass surveys may also be conducted later in the fall to determine what the expected gypsy moth population will be in these woodlots next year (2022).



Timing of the Control

The timing of the control is dictated by the development of the gypsy moth larvae and the development of the leaves on the trees. There must be an adequate leaf surface for the pesticide to be applied to, and the larvae must be actively feeding to ingest the pesticide.

Spraying must also take place with low wind and high humidity conditions, typically in the early morning or mid-evening. There will be two applications approximately 1 week apart.

The spray may take place from mid-May to early June. Best estimates at this time indicate the spray may take place anytime after May 10, 2021.

A sign will be posted at the entrance of the property to notify the public of the spraying in the County woodlots.


The application of the pesticide will be completed by Zimmer Air Services Inc.