Problem type: Environmental
Name of problem: Iron Chlorosis
Plant name(s): All deciduous and herbaceous plants
Symptoms / Characteristics:
Gradual yellowing of leaves while the leaf veins remain green. In more severe cases, leaf margins will turn brown, become dry and brittle. Affected areas may involve only a branch or one or two trees out of a group of trees. Where severe cases persist and treatment is not given, plants will lose vigor and die.
Chlorosis is caused by an iron deficiency. Iron is needed for the production of chlorophyll. Chlorophyll gives leaves their green color and is needed for the production of food and energy for the plant. Chlorosis can occur when there is a lack of iron in the soil or the iron may be there but has become unavailable to the plant due to other factors. Some factors include compacted soil, poor drainage, high pH levels and a damaged root system of the plant. Soils with high pH levels are alkaline, reading over 7 on the pH scale. High pH will make iron in the soil insoluble and in turn, unavailable to the plant. Iron is readily available when the pH is between 5.0 - 6.5.
Control / Preventions:
Treatments to correct an iron deficiency are available but are not always successful. There are a few commonly used treatments that can be used. Foliar sprays can be applied when the plant is in full leaf. An iron sulfate or iron chelate solution can be applied at a rate of 1 ounce iron sulfate in 1 gallon of water. Adding a few drops of detergent to the solution will help coat the foliage. If applying chelated iron directly on to the foliage, follow the label carefully for proper mixing and application rates. Foliar sprays should be applied during cloudy or cool days or in the evening. If treatments are successful, leaves should turn green in about 10 days. Foliar applications are only temporary treatments, affecting only the tissue that was sprayed and any new growth will be chlorotic. Several applications per year may be needed.
Another method involves the addition of iron to the soil. This is a more permanent treatment, lasting generally for one or two seasons. Iron chelates can be applied to the soil in the spring and worked into the top 5 cm of soil around the base of the plant. Water well. Results are much slower than foliar sprays but will last longer. To avoid having to amend the soil, holes may be drilled around the base starting two feet from the base and extending beyond the ends of the branches for trees. Holes should be spaced 2 -3 feet apart and drilled 8 - 10 inches deep. Following label directions, iron chelates can be poured into the holes and watered in well.
Soil amendments can be added to the soil if pH levels need to be raised or lowered. A soil test should be conducted to determine the pH as well as the availability of nutrients that can cause chlorosis. The addition of peat moss or acidic fertilizers such as ammonium sulphate will aid in lowering pH. Lime can be applied to raise the pH of an acidic soil. The results from soil amendments are not as predictable as those from the use of iron chelates.
Trunk injections are also used as treatments by injecting or implanting iron directly into the tree trunk. This method is usually carried out by a professional as it requires special equipment. Concerns have been raised about the number of wounds involved in trunk injections. The wounds are quite small and trees have the ability to close the wounds and produce callous tissue within one year.
Plants less susceptible to iron chlorosis are available and can be used to reduce or avoid problems associated with an iron deficiency.