powdery mildew of watermelon
Powdery mildew-not as important or common a problem in Indiana as it is in the southeast US. Symptoms are easily recognizable from the white talc-like symptoms of lesions.
Figure 1. Leaf lesions of powdery mildew of watermelon may be white due to the sporulation of the fungus or colonies on the reverse of the leaf may show up chlorotic. 
Figure 2. Leaf with sporulation of powdery mildew. 
Figure 3. Powdery mildew of watermelon fruit. (Photo by Wenjing Guan.) 
Figure 4. Powdery mildew on stem of watermelon.