What is causing the spots on the watermelon leaf?
A) anthracnose
B) early blight
C) a contact herbicide
The answer is that the leaf above has been affected by a contact herbicide. The herbicide caused lesions upon contacting the leaf. However, there was no growth of the lesion and no yellowing of the leaf since the herbicide caused no effect after the initial contact. While the distribution of the lesions in the photo above appears like a disease, the lack of ridges and yellowing in the leaf above is why it is not a disease. In the photo below, which is anthracnose of watermelon, the lesions have many ridges caused by growth of the lesion. Plus, there is a bit of yellowing of the lesions.
Anthracnose of watermelon.