Baking soda and water is often all we is need to treat mildew in the garden. Trouble is it’s so easy to forget or misplace the recipe. So if that should happen to you this recipe it will be archived on this site.
1 tablespoon baking soda (from the kitchen cupboard) 1/2 teaspoon liquid soap 1 tablespoon horticultural oil 1 gallon of water
Mix together and apply from a clean sprayer. The baking soda counteracts the fungi by changing the pH of the leaves, the soap helps it spread, and the oil coats the fungal spores and keeps then from growing. In a pinch, I’ve used a clear kitchen oil like canola or grapeseed as they too will smother but the lightweight hort oil is best. If you have plants you’ve not treated with this spray before start out on a small section. Plants should be well watered befoe applying and don’t apply in heavy sun. For many plants this might mean watering well in the morning and then in late afternoon/early evening come back and spray well hydrated plants when they are not in direct sun. I like to discard unused mixture after one or two days and then mix up a fresh batch. When these measures don’t seem adequate for fungal or mildew problems I apply Serenade, a commercially available and OMRI approved organic product.