GardenLine | Trees and Shrubs | Iron Chlorosis of Trees and Shrubs I

Chlorosis, caused by an iron deficiency is a common problem in fruit trees, and some ornamental and shelterbelt trees species. Iron is normally an abundant trace element in our western Canadian soils, however plant uptake of iron may be limited due to it's inavailability in high lime or calcareous soils. Other conditions may induce iron deficiency, such as: high soil pH (alkalinity), excess phosphates in the soil, excess moisture along with low soil temperatures, excess amounts of copper and manganese in acidic soils, and irrigation water containing high levels of bicarbonate ions.

Symptoms:

A gradual yellowing of the tissue between the veins of younger leaves will occur while the veins themselves stay green. This is known as chlorosis. As it advances through the plant, the tips and margins of leaves may start to turn brown and become dry and brittle. Severe cases will result in necrotic (dead) spots on the chlorotic leaves.

In other situations, where soil or irrigation water is high in bicarbonates, the leaves turn almost white rather than chlorotic. Symptoms are more noticeable after a rain or near irritation ditches.

One branch on a tree may be affected, or a few trees with in a mass planting in an area. It is not uncommon to have an affected and a healthy tree of the same species growing side by side. Eventual death of the tree is may result if the problem is serious.

Treatment:

Due to the complex nature of iron availability, treatments are not always successful, but nevertheless, these are the treatments one may wish to try:

1. Foliar Sprays: These may be effective as a temporary measure but not for complete control. Spray when the symptoms are first noticed, with a ferrous sulfate solution (28 g or 1 oz of ferrous sulfate in 4.5 L or 1 gal of water plus a few drops of mild detergent). Use a very fine mist so that the leaves will not be damaged by the solution. If the treatment is successful, the leaves should green up again in about 10 days. Repeated treatments may be required.

2. Soil applications of iron chelates: These may applied, especially in the spring. Work the chelate into the top 3-5 cm (1-2 inches) of soil around the base of the tree and water it in well. Iron chelates can be found at most garden centres under such trade name as "Tru-Green" and "Sequestrane". Although results are not as immediate as with the foliar spray, they are the most effective treatment for chlorosis and should last for 1-2 seasons.

3. Soil amendment: The use of peat moss or applications of acid fertilizers, such as ammonium sulfate may help mild cases of iron chlorosis, since it helps bring down the pH of the soil slightly. (Note: This may not be a good option if soil or irrigation water is high in salts.) The organic matter that is present and decomposing may also improve iron uptake. Results from these methods may not be as predictable as those from the use of iron chelates.

Prevention:

If iron deficiency is a problem in the area, then plants such as raspberries, currants, apples, high bush cranberries, roses, mountain ash and golden elder should not be planted. Shelterbelts species, such as the Walker poplar and Laurel willow are more susceptible to iron deficiency whereas, Northwest poplar and Acute Willow are the most resistant varieties. Other plants that are more tolerant of iron deficiency are Russian olive, lilac, cotoneaster, spruce and honeysuckle.

SOURCES:

Compendium of Apple and Pear Diseases Edited by A.L. Jones and H.S. Aldwinckle; APS, Minnesota; 1991.

Chlorosis of Fruit Trees and Ornamentals by Knud Mortensen; Saskatchewan Agriculture; Fruit and Ornamentals, Pub. 200/631.

Fertilizers and Soil Amendments by R.H. Follett, L.S. Murphy and R.L. Donahue; Prentice-Hall, Inc., N.J.; 1981.

Iron Chlorosis of Trees and Shrubs by PFRA Tree Nursery, Indian Head, SK.

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Sustainable horticultural information, offered free of charge to the public with the support of the University of Saskatchewan Extension Division, the Department of Plant Sciences and the Provincial Government.