Trees are often admired for their beautiful, lush green canopy. However, when iron chlorosis strikes, it can wreak havoc on the tree’s majestic green leaves by turning them yellow or light green. Iron chlorosis often occurs in the early to mid-summer, causing discolouration on sections of the canopy or even on the entire tree. Advanced stages of the disease can cause the leaves to turn brown and limbs to die.
While it is a common disease, treating chlorosis is easy and relatively affordable. Chlorosis in trees can only be fatal if left untreated for multiple seasons. If you plan on keeping your tree long-term, be sure to address the problem ASAP.
What Is Iron Chlorosis?
The discolouration of the leaves is a sign of iron deficiency in trees. Trees can suffer from a lack of iron due to various factors, such as weather conditions, changes in soil, and other changes in the environment. The cause of iron deficiency in trees can be difficult to determine. However, tree experts claim that low acidity in the soil can trigger this problem. Acidic soil can easily transfer iron between the tree roots and the soil. On the other hand, soil rich in alkaline tends to bind up the iron and lock it to the soil particles, making it unavailable to the tree roots. Even trees planted in red clay soil can still suffer from iron chlorosis due to high alkaline levels in the soil.
What Causes Iron Chlorosis?
For many tree owners, understanding the cause of iron chlorosis can be difficult. Many manage the problem by simply governing the availability of iron. Most trees suffer from iron chlorosis because of the presence of lime and high alkaline level (pH greater than 7.0) in soil. Despite a healthy level of iron, high soil pH can trigger chemical reactions that result in iron becoming less available. Unless the condition of the soil changes, the tree will be at risk of iron chlorosis.
Iron deficiency can also be triggered by cool soil temperatures and conditions, such as plastic sheet mulching, compaction, and water saturation. These restrict the movement of air in the soil. The problem can worsen with the removal of the topsoil since this exposes the lime-enriched subsoil.
Iron Chlorosis Treatment for Trees
Luckily, there are various methods that can be used to treat leaf chlorosis: application of elemental sulfur and ferrous sulfate in the soil, soil application of iron chelates, foliar sprays that contain chelated iron or ferrous sulfate, or injection of ferric ammonium citrate or iron sulfate on the trunk.
Pros and Cons of Iron Chlorosis Treatment Methods
| Treatment Approach | Advantages | Disadvantage |
| Soil Application of Iron Sulfate-Elemental Sulfur |
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| Soil Application of Iron Chelates |
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| Foliar Application of Iron Chelates or Sulfate |
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| Tree Injection or Implantation |
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- Soil Treatment
Soil application of iron sulfate-elemental sulfur or iron chelates can help treat iron chlorosis in individual tress and shrubs or small landscape areas in the fall or early spring. The combination of equal parts of elemental sulfur and iron sulfate can deliver long-term results and is relatively affordable. If you opt for this method, make sure to use an inorganic iron with a high concentration of iron and one derived from ferrous sulfate. Make sure to check the labels to determine the concentrations and forms of the product. It is not recommended to cover the entire landscape with elemental sulfur-ferrous sulfate combination.
Also, this treatment can be used in gardens with small shrubs. Using a hoe, dig up a small trench about 4 inches deep, 12 and 24 inches away from the plant’s base. Apply an inch of equal parts of elemental sulfur and ferrous sulfate mixture to the bottom of the trench and fill in the rest of the trench with soil. Over time, this treatment method can result in the acidification of the soil, neutralizing the alkalinity and lime in the treated areas. Iron sulfate-elemental sulfur treatment can last up to 2 to 4 years, depending on the conditions.
While iron chelates can be used to treat soil, their effect is only temporary (lasting only a year). The use of this treatment is also relatively expensive. Be sure to read the instructions on the label for application guidelines. Chelate that contains FeEDDHA molecule works well under high pH soil conditions. However, all other chelates sold in the market are inefficient in treating the soil with pH above 7.2.
- Foliar Treatment
Spray foliar treatment directly on the leaves of the affected trees during the growing season. Unlike soil application, foliar sprays respond more quickly, often in a matter of days. However, it requires the repeated application for persistent symptoms of chlorosis.
Iron chelate is often used in foliar sprays due to its efficiency in treating iron chlorosis in trees. Be sure to check the recommendations that come with the product. You can spray the foliage in the evening or on a cool, cloudy day to prevent the burning of leaves. Adding a few drops of liquid soap can help the solution cling to the tree leaves.
- Trunk Injection or Implantation
This treatment method involves placing or injecting dried or liquid iron compounds directly into the holes drilled into the lower trunk of the tree. You can use various types of capsules, plastic tubing and tees or a hypodermic-like tool to perform the treatment. While this treatment method is extremely efficient, it can cause injuries to the trunk and should be carried out with care. To reduce the risk of injury, use methods and formulations that require drilling of small holes and avoid methods that require frequent injection in a year.
Additionally, the trunk injection treatment is most efficient when applied in early spring during the bud break. The result of the treatment can last for 2 or more years. Avoid treating the tree on hot, dry, windy days as it can burn the tree leaves. Make sure to provide the tree with sufficient water for several days before and several weeks following the injection treatment.
Dave Lund Tree Service & Forestry Co Ltd helps preserve the health and beauty of your trees. If you are in need of a trusted tree care expert, call us at 905-884-0511 to book a tree service in Markham.