Birch Leafminer

• The birch leafminer is one of the most common insect pests of the river birch tree. The earliest symptoms of a birch leafminer infestation include leaves turning yellow and brown from the leafminer's feeding damage. Leafminer damage is rarely serious enough to cause health problems for your birch tree but it can leave the tree more susceptible to infestation from birch borer, another common river birch pest that is easily capable of killing the tree.
  
  

Birch Leaf Blight

• Another possible diagnosis for leaf yellowing on your river birch is birch leaf blight, a fungal disease that commonly infects river birches. Leaves infected with birch leaf blight first turn yellow and eventually defoliate. The best way to confirm this diagnosis is to remove and destroy defoliated leaves and prune the tree to allow better air circulation. This will prevent spores from the fungal disease agent spreading to other parts of the tree and your river birch should return to normal health in due time.
  
  

Chemical Soil Contamination

• Another less likely possibility is that the soil in which the river birch is growing has been contaminated with a sterilant or preventative systemic pesticide and the contamination is causing deleterious effects on the river birch tree. Yellow leaves will turn brown and defoliate, whole branches may die and any other plants growing nearby in the same contaminated soil will show similar symptoms. If these symptoms continue over successive growing seasons, the tree may need to be replanted in different soil.
  
  

Cultural and Environmental Factors

• Another common cause of leaf yellowing is simple cultural and environmental factors, of which there are many. Unseasonably high heat, a decline in soil fertility, lack of rainfall, over-watering, over fertilization, planting the tree too deep in the soil or lack of adequate growing nutrients can all cause leaf yellowing. Given the wide range of possible causes, it is difficult to confirm a diagnosis. Simply adjust cultural management practices and see if the river birch returns to normal health. If it does not, send a leaf sample to a local university extension office and have them diagnose the problem for you.