|Purdue Plant & Pest Diagnostic Lab|
"We typically only have problems with two types of fungi: powdery mildew and botrytis. With powdery mildew, which almost always appears on the cucumbers, we use a combination of water (3 gallons), vegetable oil (87 milliliters) and baking soda (9 rounded teaspoons). This is a contact spray and should be sprayed directly onto the powdery mildew spots on a regular basis (once or twice a week). We also get powdery mildew on the peppers which, unlike the cucumber powdery mildew, goes into the underside of the leaf via the stomates and is then untouched by the contact spray. To get to the underside of leaves, a trans- laminar spray must be used that goes into the leaves and kills the powdery mildew from the inside."
Read the entire interview with Rorabaugh at