Small tan, brownish spots, and holes in leaves
Small tan to brown lesions surrounded by a reddish-purple border develop in late spring can be a symptom of cercospora leaf spot. Eventually, the center of the lesion may drop out leaving a hole. Older infected leaves may yellow and die. This fungal disease affects the leaves of beet (see above photo), Swiss chard, lettuce, spinach, pepper, bean, and cucurbits. The disease is more noticeable when conditions are warm and humid.
Don't plant susceptible crops in the same spot more than once every three years. Clean up and remove all plant debris at the end of the season. Lay a dense organic mulch (grass clippings, compost) around plants and water around the base of plants, not overhead. Pick off infected leaves and pull up and hot compost badly infected plants.