• Both sweet and sour cherry trees grow in Colorado.Elisa Cicinelli/Brand X Pictures/Getty Images
  
  Most people associate Colorado with skiing, not fruit trees. Yet, when planted in full sun, fruit trees such as cherry grow well. Unfortunately, Colorado's cold climate does not keep diseases, insects, or fungus from affecting cherry trees. Black spots on cherries indicate a serious issue with several possible causes.
  
  

Leaf Spot

• Leaf spot usually attacks the leaves of the cherry tree, but some leaf spot fungus varieties also develop on the fruit. Leaf spot is the catchall name for several varieties---more than 1,000--of similar fungi; some of these leaf spot species have names such as anthracnose, downy spot, ink spot, spot anthracnose and leaf curl. The varieties that affect cherry fruits include Elsinoe and Sphaceloma. Leaf spot winters in the leaves of the tree. Leaf spot appears as small, round, dark brown, yellow, gray, purple or black shapes on leaves and fruit. In some cases, the spot appears as a coal black, raised spot. Leaf spot causes premature dropping of the leaves and increases the tree's susceptibility to other diseases.
  
  

Blackfly

• Cherry blackfly, also called black cherry aphid, spends the winter on cherry trees. Generally, these black aphids infest sweet cherry varieties over tart. The round insect causes deformity, leaf curl and black spots on leaves or fruit. The cherry blackfly leaves behind honeydew, which allows sooty mold to grow on the fruit. The spots might also result from the blackfly biting the fruit as it matures. Several generations develop on one tree; only a few of the aphids develop wings and leave the tree. They return to the tree for mating purposes. Lacewing larvae, lady beetles, syrphid flies, soldier beetles and predacious midges prey on the aphids. Chemical sprays work only at the onset of infestation.
  
  

Bacterial Spot

• Bacterial spot, caused by the bacteria Xanthomonas campestris pv. pruni, creates small circular spots, which affect the fruit and leaves of the cherry tree. Shades of the spots vary from tan to black. Also called shot-hole and black spot, bacterial spot is a stronger variety of leaf spot, which always affects the fruit. It winters in the twigs of the tree and spreads by rain to the fruit. Sprays have little effect on the bacteria, unless the spraying occurs on cherry trees before the onset of symptoms.