Leaf Septoria Treatments in Ontario Canada

I would remove the most affected leaves and maybe apply Hydrogen peroxide to both foliar and root drench. I don't know the best ratio but something along the lines of 2-8 tbp per gallon of water. you will kill some beneficial fungi In the soil doing this but if it helps you get to harvest I think it is worth it. Give your plant some Black soldier fly frass or crab meal (chitin) can help to boost its immunity.