Black Spot Plant Disease (Diplocarpon rosae) is a type of plant fungus. The Black Spot disease moves from the lowest leaves of a plant upward causing leaf drop and black spots with round perforated edges. Plants badly affected with Black Spot Disease don’t show the circular patterning since the spots combine to form a large black mass. The best treatment for Black Spot Disease is to remove the infected leaves and any fallen leaves, avoid getting the plant leaves wet, and spray the plant with a fungicide made especially for Black Spot Disease. Diluted Neem Oil is an organic non-toxic alternative for treating Black Spot Disease. Whichever product you choose, spray every 7-10 days during the warmest part of the growing season since the fungus is most active when the temperature is between 75 to 90 degrees Fahrenheit. Keep any plants infected with Black Spot Disease away from your other plants.