Pumpkin and squash mildew kills plants.

Powdery mildew, a common problem of roses, turfgrass and many other plants, also is a problem for squash and pumpkin especially when we experience the cool, humid conditions of fall.

This fungal disease destroys the photosynthetic ability of the leaves reducing the quality, size and yield of the fruit. 

The first syptoms you will see are white spots on the leaves.  These spots increase and eventually cover the leaf. This disease reduces the sugars and starches necessary for the development and sizing of the fruit.

Controlling this disease is quite easy if you use the correct product or combination of materials.  Some people use SunLite oil in combination with baking soda as a spray.  A better product to use is potassium bicarbonate.  Baking soda can damage plant cells; potassium bicarbonate is much softer in its activity.  Neem oil is also reported to be an effective control of powdery mildew.  Your local nursery or garden center should have one of these products on their shelves.

These products are best applied in the evening as they remain in the liquid state for a longer period of time.  If a rain occurs shortly after you make the application you will most likely need to reapply the product.  You will still see spots on the leaves even after you treat for this disease, but as long as the spots don't enlarge or more spots don't develop, the infection has been stopped.  Follow the label to ensure you apply these at the proper dilution and frequency.