• Healthy, blooming cherry treeTravelif/Photodisc/Getty Images
  
  The leaves of a healthy cherry tree should never turn yellow until fall, when they can be a show of orange and red, too. At any other time of year, yellow leaves are an indicator of a serious problem. Yellowing is not likely to be caused by leaf-eating insects, fungus or boring insects. Those critters are more likely to cause brown or blackened leaves with holes in them. Determine the cause of yellowing in your cherry's leaves before deciding on a course of treatment.
  
  

Iron Chlorosis

• Look for symptoms of iron chlorosis, which causes yellowing of leaves due to an iron deficiency. Yellowing starts at the edges of the leaf, moving to the center. Veins tend to remain green throughout this process. According to Colorado State University, iron chlorosis can start in a single, cold-injured branch. Cherry trees, like most fruit trees, are susceptible to winter injury. Iron chlorosis is difficult to treat and simply adding iron to the soil doesn't really help. Good cultural practices like aerating soil, amending clay soil with peat and organic compost and reducing springtime watering are often more effective.
  
  

Overwatering

• Where dehydration can cause cherry leaves to turn brown and drop, overwatering causes yellowing. According to Utah State University, cherry trees planted in lawns tend to get too much water. If this is your problem, stop watering the lawn near the tree. Chop out the grass over the root zone of your cherry tree, and cover it with 2 to 4 inches of mulch. Don't let mulch pile up against trunk bark, where it will cause rot and host of new problems. Water the tree every three weeks, allowing it to dry out considerably between waterings.
  
  

Prune Dwarf Virus

• Look for signs of prune dwarf virus on sour cherry trees. According to Oregon State University, this virus can be transmitted through budding and grafting practices, and by infected pollen that circulates on air currents during bloom. Symptoms appear in summer, with a green-yellow mottling on the leaf surface. Eventually, 30 to 50 percent of the leaves drop early. Prune dwarf virus doesn't kill cherry trees outright, but leads to a gradual decline. Once the tree is gone, don't plant another one on the same spot for at least three years to avoid infecting new trees.