About Chlorosis

• Chlorosis is a disease that most commonly damages Northern red oak, white oak, and pin oak trees. This disease is most often seen in oak trees planted in clay alkaline soils with a pH of 7.8 or greater.
  
  

Causes

• Chlorosis is caused by the oak tree's inability to absorb necessary amounts of iron and manganese. Healthy leaves use iron from the soil to make chlorophyll, which is responsible for giving the leaves a rich, dark-green color. High soil levels of phosphorus and potassium can also cause chlorosis in oak trees because it prevents the roots of the tree from being able to absorb iron.
  
  

Soil Conditions

• Alkaline soil is any soil with a pH of 7.0 or greater. Unfortunately, many urban lawns and landscapes feature alkaline soils due to the construction materials used to build homes, buildings and roads. If the soil is compacted and poorly drained, it provides even worse growing conditions for the oak trees. Compacted soils contain less oxygen and cause further damage to the tree.
  
  

Symptoms

• Oak trees damaged by chlorosis will start to display yellowed leaves in the early summer months. This disease can be identified by inspecting the leaves. Leaves will be yellow in color but veins running through the leaf will remain green. As this disease progresses, the yellow leaves will develop brown spots, which are portions of dead leaf tissue. Severe cases of chlorosis will eventually kill the entire tree because the growth of new shoots will be stunted.
  
  

Treatment

• The best way to treat chlorosis is to control the pH of the soil with the application of sulfur. Unfortunately, this treatment only corrects the top inch of the soil and doesn't always yield the desired results. Another method of treatment is to apply chelated iron to the soil. This organic iron replenishes the iron within the soil. Each application will correct soil conditions for 1 to 2 years. Some fertilizers available at local garden centers also advertise an ability to adjust soil pH levels. When using any products purchased at retail, follow manufacturer's instructions carefully.