The first week of August I always recommend an application of Actinovate and RAW Silica to the pumpkin leaves to help battle powdery mildew and other leaf diseases. At this point of the season older leaves become vulnerable to diseases as they lose their resistance due to age. Once these leaves get infected they become the base camp to spread spores to other leaves and then you can start getting problems. Actinovate is a biological fungicide that I've found to be effective in helping keep powdery mildew at bay. Once you have powdery mildew it can only help minimally, but if you start applying the end of July and beginning of August you'll find your leaves do considerably better to the end of the season. You'll still get some powdery mildew, but it will be controlled much better than without it.
RAW Silica is a biogenic silica that works as part of the systemic resistance of the plant. The plant takes the silica to the points of infection and crystalizes the cells around the infection to make it more difficult for the disease to spread. Unlike most silica products on the market, the RAW Silica is Ph neutral so it isn't as high in Ph as most products which makes it more friendly to beneficial bio organisms. You can't over use a biogenic silica, like you can a potassium silica, because the plant can only take in so much, so you can use it every week to get the multiple benefits of silica.
The Actinovate I applied earlier this week I noticed was past its expiration date so I reapplied from a new bag today along with the silica.