Iron Chlorosis of Trees and Shrubs
Iron deficiency chlorosis is a common problem in fruit trees and certain ornamental and shelterbelt species in western Canada. Although iron is an abundant trace element in soil, plants may have difficulty in absorbing enough in high lime or calcareous soils. Other conditions which can induce iron deficiency include high soil pH (alkalinity), excess phosphates in soil, excess moisture along with low soil temperature, and excess quantities of copper and manganese in acid soils.
The first symptom is a gradual yellowing of the tissue between the veins on younger leaves while the veins themselves tend to stay green. If unchecked this condition may advance throughout the plant causing the tips and margins of some leaves to turn brown and become dry and brittle. Often a branch of a tree or perhaps a few trees in an area may be affected. It is possible to have an affected and healthy tree of the same plant species side by side. In severe cases, entire trees can lose their leaves and die.
Because of the complex nature of iron availability, treatments are not always successful. However, there are several treatments to choose from.
- Foliar sprays: At the onset of symptoms spray leaves with a ferrous sulphate solution (28 grams or 1 oz. of ferrous sulphate in 4.5 litres or 1 gal. of water plus a few drops of mild detergent). Spray as a very fine mist. If the treatment is successful the plants should begin to green up about 10 days after spraying. Foliar applications are a temporary measure and successive treatments may be required.
- Soil application of iron chelates: Apply iron chelates to the soil in the early spring by working them into the top 3 to 5 cm of soil around the base of the tree and watering well. Iron chelates are available from most garden centres under such trade names as "Tru-Green" and "Sequestrant". Soil application of iron chelates is the most effective treatment for chlorosis. Results, while not immediate, should last for one to two seasons.
- Soil amendment: Since iron is less available in soils with a high pH the addition of peat moss or the use of acidic fertilizers such as ammonium sulphate may help in mild cases. The presence of decomposing organic matter may also improve iron uptake. These methods are considerably less consistent than the use of iron chelates.
- Prevention: When the condition is known to persist in an area, then susceptible plants such as raspberries, currants, apples, high bush cranberries, roses and mountain ash should not be planted. For shelterbelts, Walker poplar and Laurel willow are also subject to iron deficiency chlorosis, while Northwest poplar and Acute willow are the most resistant varieties.
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