SYMPTOMS AND EFFECTS

Chlorosis is a common problem of trees in Michigan. Some trees are more susceptible than others, but it is a potential problem in all trees.  Chlorosis is usually evident for many years and, left untreated, may end with the loss of the tree.

Chlorosis generally starts as a yellowing of the leaf tissue which can show as a pale green leaf when the leaf would normally be dark green in color.  As the condition worsens the leaves will lose their ability to manufacture food and will fall from the tree. Chlorosis reduces the ability of the tree to produce food.  As the tree loses its ability to produce food it will rely more on its stored energy. As the tree depletes this stored energy, whole branches and portions of the tree will begin to die. Over time the tree may decline enough to lose its aesthetic value, necessitating removal.

CAUSE

Chlorosis is caused by the tree being unable to produce chlorophyll. This is usually caused by a deficiency of essential micronutrients like iron, manganese, zinc or copper. Many times, this is caused by a soil pH that the tree is not suited for, or by a low level of nutrients in the soil, and in some cases even from an injury or disease causing a problem in the trees roots or stem limiting the amount of nutrients the tree can absorb and deliver to the leaves.

In the case of chlorosis caused by the soil pH, what is happening is that at different pH levels different nutrients are available in the soil. One common instance of this happens in Michigan oaks planted in soil with a pH level that is too high, causing the iron in the soil to bind with the soil making it unavailable to the tree. For this reason, your arborist may suggest taking a soil and foliar sample to assess the nutrient levels in both the soil and the leaves to confirm or rule this out as a possibility.

CONTROL

Prevention is the best option. The best way to prevent chlorosis is to research plants you would like to have in your landscape to confirm they are suitable for the pH level of your soil. When planting be careful not to damage the roots, and protect the roots during any construction projects going on around the tree.

If the problem is related to high soil pH, a pH reducer can be added to the soil to lower the current pH to an acceptable level. This can be a long process as soil pH can be difficult to change. Another option is to supply the plant with the lacking nutrient through either a soil injection where a nutrient rich fertilizer is added to the soil, or a trunk injection where the nutrient is injected directly into the trunk of the tree. Trunk injection shows the fastest results but in general should only be used to aid the tree while the underlying issue is being addressed.
The goal is to lower the soil pH to a level that the soil and tree are in balance and maintain that level in the future.

ALTERNATIVE PLANTING OPTIONS

If a lab test determines you have a high pH soil, there are several tree and shrub species available that you can plant that will tolerate a high soil pH. You should also be aware of the types of tree species in Michigan that will not tolerate high pH soil so you don't waste your time and money on a plant that will not thrive.

Photo:  Joseph O'Brien, USDA Forest Service, Bugwood.org