Iron Chlorosis in Pin Oak and River Birch

Summer is full of colorful blooms and foliage in the landscape. But some colors are not as welcome as others. Yellow leaves in summer could indicate plant problems. Yellow leaves on specific plants such as Pin Oak and River Birch could be signs of underlying nutrient issues like iron chlorosis.

Chlorosis

When leaves yellow they are sometimes called chlorotic. Overall yellowing of leaves could be caused by lack of nutrients like nitrogen, limited or reduced light, overwatering, or many other environmental issues. When the leaf blade is yellow and the veins remain green, it is called interveinal chlorosis. Interveinal chlorosis is often associated with nutrient disorders, especially micronutrients iron and manganese. 


Pin oak chlorosis. Photo courtesy of ISU PIDC. 

Nutrient availability

Plant nutrients are essential for plant growth and reproduction. Nutrients are divided into two categories: macronutrients and micronutrients. Macronutrients are nutrients that plants need in large quantities. Nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur are the macronutrients often supplied in commercial fertilizers. Micronutrients are equally as essential for plant growth, but they are needed in smaller quantities. Micronutrients include iron, manganese, copper, boron, molybdenum, zinc, chlorine, and nickel. A lack of iron or manganese can easily cause interveinal chlorosis in river birch and pin oak.

While most nutrients are readily available in the soil, sometimes the soil’s pH interferes with the availability of a nutrient. For example, iron is often unavailable to plants in alkaline or high pH soils. Therefore, iron deficiency symptoms show up as interveinal chlorosis in certain plants in alkaline soils.

Treatment options for iron chlorosis

There are few easy fixes for pin oaks and river birch with iron chlorosis. Trees can be treated with iron injections, preferably by an arborist. Injections will green up the leaves for a short time, but will need to be reapplied for the life of the tree. Changing the soil pH around the tree is another option. Elemental sulfur will lower the pH is some soils. However, drastically changing a soil’s pH is very difficult and not long-lasting. The final option is simply to remove the tree. Some species (like Pin Oak and River Birch) are more sensitive to iron deficiencies than others. White or red oak, honeylocust, linden, and many other shade trees are adaptable to soil pH and rarely have issues with iron chlorosis.

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