Watermelon Diseases Powdery Mildew Powdery mildew causes a white powdery growth on the leaves. The crown leaves are affected first and may wither and die. Disease development is favored by high temperatures. The first symptoms are small, circular, watersoaked, leaf spots. The spots grow together and affect large areas of the leaves.
Defoliation starts with crown leaves.
The disease overwinters in seed and diseased crop residues. The disease is easily spread with weak plants most susceptible. The first symptom is water soaked spots which later turn black. Elongated dark spots with light centers form on petioles and stems causing death to plant parts beyond the infection. Young fruit may be killed.