Iron Chlorosis In Trees
The past few years, I have noticed several trees with leaves that are more yellow than normal. This condition is called iron chlorosis. The most common trees associated with this condition are pin oaks and silver maples. Other trees that are susceptible are sweet gum and baldcyprus. White pine, sugar maple, red maple, sycamore, ornamental pear and some crabapple are other common species that may develop iron chlorosis. If you have some of these varieties of trees and as your trees leaf out this spring, you may want to check and see if the leaves are yellow.
Why does iron chlorosis develop? Iron chlorosis can occur if iron is either deficient in the soil or unavailable to trees. Under most circumstances, iron is plentiful in the soils in our region and is available to trees growing in soils with a pH of 5.0 to 6.5. In soils with a pH of 7.0 (neutral) or higher, iron is converted to an insoluble form that is less available to growing plants. High levels of copper, manganese or zinc in the soil and excessive applications of phosphorus fertilizer will also contribute to the problem. Treatment of iron chlorosis can be expensive so if you are planting new trees, selection of trees that are less affected by low iron availability is recommended.
Iron is very important in producing chlorophyll, the green pigment in leaves. If there is a deficiency iron, less chlorophyll is produced and a yellowing of leaves occurs. On deciduous trees, the leaf veins remain green while the area between the veins is yellow-green to yellow. Leaves that emerge later in the year may be smaller and more yellow. Under severe cases the leaves may turn white and finally brown. If left untreated, branches may dieback and the tree may eventually die after several years.
How do I know if my tree has iron chlorosis and what can I do about it? Soil testing is the easiest method to determine your soil pH and other nutrients available to the tree. This should be done before any treatment for iron chlorosis. Take soil samples to about a 6-8 inch depth at several locations around the tree and mix together. You need about a pint of soil for testing. Your local county Extension Educator can submit your soil sample to the University of Nebraska Soil Testing Laboratory for analysis. The fee is about $10, depending upon how extensive analysis you have.
If a high soil pH is confirmed there are several methods to provide iron to your tree. Adding iron through foliar application, soil amendments, trunk injection and trunk implantation are methods of treatment. If a rapid response is needed, foliar application may be applied to the leaves when the tree is fully leafed out. Soil treatment by adding iron, in the form of ferrous sulfate and also lowering the pH with the addition of sulfur is a more permanent way of correcting iron chlorosis; unfortunately it is more difficult. You need to drill several holes in the soil, add the mixture of ferrous sulfate and sulfur and cap them off with soil. For best results, treat the soil in the spring. Iron compounds may also be injected or implanted into the trunk to correct the problem. These treatments should be applied in May or June for best results. Later treatments are often not as effective. For more detailed information on iron chlorosis in trees contact me at the Nemaha County Extension office at (402) 274-4755. We have the NebGuide G94-1218 “Iron Chlorosis of Trees and Shrubs” available that provides detailed treatment guidelines.
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