I am growing cucumbers in a container this summer. The leaves suddenly developed brown spots. The plant is still producing cucumbers.
Anthracnose or one of the other fungal leaf spot diseases can cause the damage you described. Prevent these diseases by growing cucumbers, melons and other vine crops in full sun with good air circulation. Growing vine crops, even those in containers, on trellises will help increase air circulation and decrease disease problems. Avoid overhead watering whenever possible. Fungicides can be used to reduce the spread of this disease. Apply a fungicide labeled for use on vegetables as soon as the disease appears. You will need to repeat these sprays every 10 to 14 days during wet weather. Read and follow label directions carefully. Fall sanitation will help reduce the source of disease for next season.