powdery mildew of pumpkin
Powdery mildew
Figure 1. Powdery mildew of pumpkins can be easily recognized by the talc-like lesion on the upper and lower surface of leaves. 
Figure 2. A fungicide trial for products for powdery mildew of pumpkin. The untreated row on the right has significant symptoms of powdery mildew. The adjacent row to the left has been treated with a systemic fungicide and has relatively mild symptoms. 
Figure 3. Severe symptoms of powdery mildew on a pumpkin leaf. 
Figure 4. Powdery mildew lesions can be observed on the lower leaf in this photo. The upper leaf has light colored variegation that are sometimes mistaken for powdery mildew.