I have a natural trick for mildew and black spot for your roses. Baking soda and water. It’s simple and it works. You have to start at the beginning of the season when the leaves come out and religiously spray once a week before any mildew shows up – it’s a great preventative. Mix 1 tsp baking soda per liter of water and put it in a spray botte. I have also heard people using 1 tsp vegetable oil,1 tsp vinegar,1 tsp baking soda per 1 liter of water, but I have only used baking soda and water. Do you have any natural ways for a fungicide ?