Powdery mildew is one of the most frustrating and recognizable plant diseases a gardener will experience. Depending on the plant type affected, it can either be merely unsightly, or it can cause a reduced yield of buds and fruit, and can affect the flavor of what does appear.
What plants are susceptible to powdery mildew? Well, there are several strains, and because of that, most plants are susceptible to one form or another. You see it a lot in roses, lilacs, cannabis, zinnias, and several food-bearing plants like beans, cucumbers, squash, grapes, and melons.
Usually, powdery mildew will not actually kill your plants. It’s definitely ugly and frustrating, but not usually fatal. However, it can be very tricky to get rid of. In fact, the best thing you can do is prevent it in the first place. If you don’t over-plant an area, that helps a lot. An oddity about powdery mildew – it doesn’t require direct contact with water to spread, like most other mildews. It does, however, grow best in humid, warm climates with cool nights. So basically, it does best in late summer.
Keeping this in mind, it’s best not to use a nitrogen-rich fertilizer in late summer, as nitrogen encourages growth of succulent tissue, where powdery mildew does best. Plants also are more resistant to powdery mildew when they are healthy, and fed the nutrients they need early on in the season. MKP (mono-potassium phosphate) has been shown to suppress powdery mildew, and it’s great because the dry ratio is 0-52-34, so you won’t be adding any nitrogen at this critical time. Used as a foliar spray, you’ll see great results in suppressing the powdery mildew. If you’re someone who likes options, you could also use Mighty Wash, which you can find at almost any hydroponic shop.
So basically, you won’t normally lose a plant from powdery mildew, but you’ll definitely feel its’ effects. Get rid of the affected areas of the plant if you can, and don’t compost them. Normal compost temperatures aren’t hot enough to kill the spores. Make sure you give your plants plenty of air circulation by not over planting in any one area, and give them the right amount of sunlight on their leaves (certain plants, of course, are more shade-loving, so double-check before you plant one in an area that’s too sunny). This helps to inhibit spore germination in the first place.