Red spots on your apple tree's leaves is a fungus called rust. Once you can see the marks, it is too late to treat.
Start spraying in the spring:
- when the buds begin to form and swell
- and then again after the buds open
- and once more about 10 days after they open
Home Depot sells "Defender Garden Fungicide", sulfur based, sold online only.
Canadian Tire sells "Defender Garden Fungicide", sulfur based, carling AISLE 75
Called Ritchie Feed & Seed, they also carry a sulfur spray. He said you need a license for Serenade
Serenade Garden is a broad spectrum biofungicide, Serenade Garden contains a patented strain of Bacillus subtilis. Provides protection against many of the most common fungal and bacterial garden diseases (see label). Now you can grow beautiful disease-free fruits, vegetables and flowers – without chemicals that can be harmful to people or the environment. It is so safe you can confidently harvest and eat fruits and vegetables the very same day they are treated. Will NOT harm bees or beneficial insects.