Watering

• Brown or black spots appearing on the leaves could be the result of over or under watering. If the spots or patches are crisp and brown, then under watering is the probable cause. If the areas are soft and dark brown or black, then the plant may be over watered. Check the soil dampness and drainage system.
  
  

Sooty Mold

• This is a black fungus that grows on the sticky substance known as honeydew, which is deposited by aphids. The mold does not harm the plant, but does reduce growth by blocking its pores. Mold can be removed by wiping with a damp cloth. Control future attacks by spraying against aphids.
  
  

Leaf Spot

• Leaf spot -- caused by both bacteria and fungus -- makes brown or black moist spots appear on the leaves. These spots can enlarge and merge, killing the leaf. Keeping the leaves dry can control the problem. Infected plants should also be kept away from healthy plants until the spot has cleared up. Infected leaves should be removed.