Appears in midseason on the oldest leaves and spreads to younger leaves. Enlarging, circular brown spots with rings form on the upper leaf surface and are later covered by black, moldy growth. The fungus is seed-borne and overwinters in crop debris and weeds.
If possible, don't plant cucurbits where they have been grown within the last 2-3 years. Avoid overhead watering. Apply a copper soap fungicide routinely to reduce infection and slow its spread. We recommend Soap-Shield® Flowable Liquid Copper Fungicide.