I love to grow pumpkins, mostly because I don’t have to do anything. You plant them in good soil, water, wait, and comparatively gigantic fruits appear a couple months later. One can grow the classic orange pumpkins (‘Jack-O-Lanterns’) or go for something more decorative, like ‘Kakai’ (picutred). Regardless of variety, one thing always seems to happen to homegrown pumpkins: they get powdery mildew in August.
Powdery mildew is that white, powdery coating you see oftentimes on large-leaved plants in early fall. It usually comes from cool, moist nights and hot days. In early years, I tried to treat this fungus with fungicide, which is fairly useless, since it’s only a preventative treatment. Once the plant has the spores, it’s sort of done for. You can lower the spread by watering only at the base and keeping the leaves as dry as possible. Sometimes that takes time, so in recent years, I’ve given up and allowed the powdery mildew to take over. Good choice or bad?
Well, I’ve never had a rotten or spoiled pumpkin yet. I just keep watering in August and September and let the leaves wilt and dry up as they may. But I did contact Washington State University Extension Horticulturalist Linda Chalker-Scott to find out just how dangerous powdery mildew is to a plant. “It’s not dangerous at all,” she said. “The only impact it has is to decrease photosynthesis, but at this point the leaves are getting old anyway. It would be more of a problem on younger plants.” So, if you’re growing pumpkins and you notice powdery mildew after the fruits have formed, don’t worry about it. Keep watering. You’ll have spectacular pumpkins anyway — and a happy Halloween.