Powdery mildew has appeared on my squashes-both winter squash and summer squash. Powdery Mildew is a fungal disease that affects many plants from roses to squashes. Infected plants display white powdery spots on the leaves and stems that eventually will cover the leaves of the plants if left untouched. Powdery Mildew grows well when the monsoons come into Santa Fe. The higher humidity and moderate temperatures are idea for powdery mildew. Also how we manage our gardens can cause it to go rampant. For instance, I planted my winter squash too close to some other plants essentially crowding them. Plus fearing a hail storm this summer, I covered it with some hoops and row cover, holding the heat and humidity underneath creating a perfect environment for powdery mildew. It usually shows up in late August through September.
Controlling it depends on when we catch it. If we let it go too far, it will destroy the plant in which case we should pull the plant and destroy or bag it for refuse. Do not put it in you compost pile and spread the disease around. If it has just started, indicated by the white spots on the leaves, you can spray it with a fungal disease spray like Green Cure. Green Cure is my favorite spray for Powdery Mildew as it is quite effective in halting its progress but you will have to spray it 2-3 times depending on how advanced it is on the plant. We should jump on it as soon as we see it and not wait till it gets out of hand.