This disease looks very much like scorch. Rake up and destroy old leaves. No chemical control is available. A leaf spot disease will cause small brown circular spots on the leaves. No chemical control is listed.
Powdery mildew covers the undersides of the leaves with white mold.
Sprays of fungicide should bring the disease under control. Anthracnose may infect terminal shoots several inches from the tip. The infected area is shrunken and the outer layers of tissue may be ruptured. Leaf scorch is a physiological problem. The leaf margins turn brown then browning moves progressively inward between the veins.