Poinsettia scab (Sphaceloma poinsettiae) is a fungal disease that causes circular, cream-colored spots on the midribs and veins of leaves and raised, often elongated lesions on stems and leaf stalks. Severely infected leaves may drop off the plant prematurely. Scab is most prevalent in the summer months. Scab-infected branches should be pruned out and discarded as soon as they are noticed. If the disease has spread throughout a plant to the point that pruning out the diseased parts is not possible, the whole plant should be removed and disposed of. Products containing mancozeb, thiophanate-methyl or chlorothalonil can help to prevent the spread of the disease to healthy plants.