Aerial Spraying in B.C.'s Forests

HealthLinkBC File Number: 
Last Updated: 
April 2015

What insects are being treated?

B.C.’s forests are home to many defoliating insects, which are insects that eat the leaves of trees and shrubs. Most of these species cause little to no serious damage to the plants they feed on, however, there are a few species that do.

The BC Ministry of Forests, Lands and Natural Resource Operations (FLNRO) is concerned with lessening the damage and protecting our trees from the following moths:

  • Western spruce budworm
  • Douglas-fir tussock moth
  • Western hemlock looper

Why are these moths a concern?

These moths are aggressive feeders and can strip the leaves from their host trees (defoliation). The damage from this defoliation can cause growth loss, stem deformities and even the death of the tree.

Human exposure to airborne Douglas-fir tussock moth hairs, silken threads, and shed skins during large-scale infestations have caused allergic reactions such as skin rash and possible upper respiratory tract symptoms. Unfortunately, outbreaks usually occur in low lying areas that are often populated by people. Exposure can cause a lot of discomfort and inconvenience to people who live in affected areas.

How are these moth populations being controlled?

Many methods are used to monitor defoliator populations in B.C. These methods include pheromone trapping, egg counts, and defoliation mapping to monitor populations.

Aerial spraying with Foray 48B® is used for minimizing damage caused by defoliator populations over large or difficult-to-access areas. It is also approved for use on certified organic farms.

Foray 48B® is a water-based product containing a bacterium called Bacillus thuringiensis variety kurstaki (Btk). Btk is a bacterium found naturally in soil. It is known to affect only caterpillars usually only during the early larval life stages if it is ingested while they are feeding.

In addition, Foray 48B® contains a number of inert (inactive) ingredients which improve the performance of the Btk. Many of these ingredients are approved food grade additives. No petroleum products are used.

Foray 48B® is not harmful to people, dogs, cats, fish, birds, reptiles, or insects such as honeybees, beetles or spiders. Btk pest control products have been registered for use in Canada for about 40 years. It is now the most widely used pest control product in the world.

What happens during aerial spraying?

Aerial spraying of Foray 48B® is usually done in the early summer between early June and mid-July depending on the insect species and the weather. Spraying takes place very early in the morning (around 5:00 am) which is usually the calmest part of the day. Spraying may continue throughout the day as long as the weather is suitable. Each area is usually treated only once during a season. These applications are timed to treat young caterpillars when they are most vulnerable to the effects of Btk. Depending on the size of the treatment area, the aircraft used and weather delays, it may take several mornings to complete one application.

The treatment area may appear larger than it actually is because the aircraft make turns in areas outside of the treatment area. Spraying is carefully controlled by GPS navigation equipment and only occurs over designated areas.

You will not be directly told of the timing of the aerial spraying, but the general treatment period will be posted on signs near the treatment areas. For more information on treatment dates by location, visit the Ministry of Forests, Lands and Natural Resource Operations website at

You may notice a musty smell and spray droplets on hard surfaces and windows after the treatment. Droplets can be removed with water and a bit of scrubbing, but these will eventually disappear on their own.

Are there any health concerns?

There have been 2 extensive public health monitoring studies in Vancouver and Victoria. The results have not shown any increase in illnesses seen by health care providers or in hospital emergency room visits due to spraying. As well, the monitoring has not shown evidence of harmful effects on children with asthma or those with weakened immune systems.

If you wish to avoid contact with the spray, it is recommended that you stay indoors while your property and nearby areas are being sprayed. You should wait until the spray has dissipated (dispersed) before going outdoors. This will usually take about 30 minutes. If you have health conditions and are concerned, you should speak to your health care provider.

In addition to staying indoors during the spraying, you should also follow standard good hygiene practices. These include:

  • Wash your hands throughout the day, especially after gardening, after going to the bathroom, and before preparing food.
  • Wash all fruits and vegetables before eating or cooking.
  • Maintain home swimming pools.
  • Clean or wipe indoor and outdoor equipment at daycare centers and preschool facilities, as well as covering sandboxes or sandpits when they are not in use.

Is it an emergency?

If you or someone in your care has chest pains, difficulty breathing, or severe bleeding, it could be a life-threatening emergency. Call 9-1-1 or the local emergency number immediately.
If you are concerned about a possible poisoning or exposure to a toxic substance, call Poison Control now at 1-800-567-8911.

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