Have you ever seen a pin oak with yellow leaves? There are plenty of them in this part of Kansas, and now (early spring) is the best time to do something about it.
Iron chlorosis is the official name of the leaf-yellowing phenomenon. Iron chlorosis typically occurs in soils with a pH of 7.0 or more, when iron changes to an insoluble form and is unavailable to plants. While pin oaks are the most commonly affected, white pine, river birch, sugar maple, red maple, baldcypress and others are also susceptible to the condition.
The best way to avoid iron chlorosis in your landscape is to choose plants that are tolerant of high pH and low iron availability. If the plants are already in place and you have noticed consistent yellowing, remove the plantings or work to correct the problem.
Test the soil around the tree or plant. Dig samples from 6-8 different spots within an area near the tree and mix them together. Then put about 1 1/2 cups of soil in a bag or container and bring it to the Douglas County Extension Office for testing. If only one side of the tree shows symptoms, test separate samples from different sides of the tree.
Soil test results provide information about pH of the soil and recommend how to correct pH if needed. Acidifying the soil is usually the best way to remedy iron chlorois, but it may be the most difficult.
Follow soil test recommendations to lower pH. Sulfur, iron sulfate and aluminum sulfate can be applied to bare soil. Soil covered with turfgrass is more difficult to remedy and may require professionals to inject iron sulfate or chelated iron into the soil. Injections typically help for two to three years.
Distribute iron tablets around the base of the tree. Although it is sometimes difficult to get the tablets evenly distributed, they contain a quick-release iron complex and sometimes sulfur that helps acidify the soil. Read and follow all label instructions if using iron tablets.
Another method is to inject or implant iron sulfate, iron ammonium citrate or iron chelate directly into the tree trunk. Some of these products are available to homeowners and can be purchased at many local garden centers. Read and follow all label instructions when using iron capsules.
Other injection and implantation systems, such as Mauget, Medi-Ject and Nutri Booster must be applied by a professional.
Leaves occasionally yellow for reasons other than iron chlorosis. Fungal leaf-spotting diseases and insects sometimes cause irregular yellow patches on leaves. Mineral deficiencies other than iron are less common but display similar symptoms. If you are unsure, consult a professional.
Although today's temperatures offer no evidence of spring, the official change in seasons is just around the corner. Take some time to prepare your trees before the growing season arrives.