Health Canada is advising Canadians to not use malathion products older than one year

Health Canada is advising Canadians to stop using pesticides that contain malathion when products are older than one year due to chemical changes in the product over time. In Canada, malathion is a registered insecticide mainly used to control insects in agriculture, but it can also be used in and around the home. When used according to label directions, malathion is effective in killing mosquitoes and other pests without posing unacceptable risks to human health or the environment. However, over time a toxic chemical called isomalathion can naturally form in malathion products, particularly when they are stored at elevated temperatures. After storage for more than a year, it’s possible that levels of isomalathion could become a concern, even when containers are stored correctly.

Make sure any products containing malathion are stored in a cool (around 20-23°C), dry, well ventilated place away from seed, fertilizer or other pesticides and for no longer than one year.