This rose disease is caused by a fungus on rose canes and fallen leaves that thrives in warm, moist environments. Spores spread to other plant parts via splashing rain or overhead watering. It appears on young leaves as black circles with irregular margins. It grows to about 1″ wide and may be surrounded by a yellow halo. Leaves may turn yellowish and drop and in severe cases roses will loose all their leaves. A new crop of leaves may appear only to be lost again. Give roses maximal sun and good air circulation. Water during hours of full sun so leaves can dry before nightfall. Avoid overhead watering, remove all old leaves, apply a thick mulch in early spring to reduce water splashing that transfers fungus spores. At first appearance of black spot you can spray leaves thoroughly with a fungicidal soap, liquid sulphur, or a Neem Oil product. Rose Defense can be purchased at our nursery.