You may be wondering why some of the trees in your landscape turn a yellowish- green color in the summer months. The most common cause for this in the Midwest is a lack of micronutrients ( or mineral elements )that are essential for the growth of plants, but only needed in very small quantities. Micronutrients include iron, manganese, zinc, copper, boron, silicon, and molybdenum. These are in contrast to macronutrients (nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur), which are required in larger amounts and make up a larger portion of the plant tissue. This yellowing is typically a sign of a lack of these nutrients in the trees.
What are symptoms of micronutrient deficiency?
The most common micronutrient deficiencies seen in trees are iron deficiency of pin oak and river birch, and manganese deficiency of maples. Both deficiencies are marked by pale green or yellow leaves, with veins that remain green. As the deficiency continues, new growth is stunted, branches may die back, and the margins and interveinal areas of leaves may become brown. In severe cases, the entire tree may decline over several years and die.
What causes micronutrient deficiencies?
Micronutrient deficiencies, most commonly iron or manganese, are actually not caused by a lack of these mineral elements in the soil. Usually the soil has plenty of these elements, but at high (alkaline) pH, they are in a form plants are not able to take up through their roots. Micronutrient deficiencies also may occur when a plant’s root system is compromised, such as by injury, disease, poor site conditions, drought, or saturated soils.
How can my trees be treated?
The best way to avoid poor plant health caused by micronutrient deficiencies is to test the soil before planting a tree and choose trees that are tolerant of the high PH soil conditions.
In the case of an established tree suffering the effects of a micronutrient deficiency, several strategies can be used to improve the health and vigor of the tree, although none are easy or permanent. Foliar application of iron is a short-term treatment that can help trees appear more green and healthy in the current season, but must be applied later on when leaves have emerged.
Micronutrients also may be injected into the trunk of the tree. These treatments help leaves to turn green within a week or two, and can last up to two years. Liquid Chelated iron injected directly into holes drilled into the trunk has proven to be one of our most effective treatments of iron Deficiency in oaks and birch trees.
Additional Soil treatments may also help. An Iron / Sulfur combination applied directly to the soil around the base of the tree will also be beneficial and improve the appearance of the trees.
Maple Trees with yellowing leaves and green veins are an indication of Manganese deficiency. This is more common with Maple trees growing in sandy soils. Manganese tree implants are available to treat trees in this condition.