Badly affected leaves turn brown and drop off. If wet weather persists, melon and cucumber fruits develop soft dark spots that become sunken rot spots.
Because anthracnose is a wet weather disease, growing cucumbers and melons at proper spacing, so sunlight reaches all the leaves and air circulates freely, is a sound preventive measure. Avoid low places with repeated heavy dews when choosing a place to grow melons, and use mulch to keep soil from splashing onto new leaves. Many varieties offer some genetic resistance. This disease can be carried on seed, so buy only disease-free seed and do not save seeds from infected plants.
If the damage is limited and dry weather is predicted, you can wait in hopes that dry conditions put an end to the problem. If more than one third of a plant’s leaves are lost to disease and the immature fruits show suspicious spots, it is probably a waste a time to wait on the crop. Pull up the plants and compost them.