Iron Chlorosis of Azalea

Dr. John F. Baniecki
WVU Extension Service
Plant Pathology and Entomology Specialist
August 2000

Iron deficency appears to be one of the most common causes of chlorosis of the foliage of azalea. However, several other factors cause yellowing of this plant, such as poor root growth, heavy compacted soil, poor drainage, overwatering, low temperature, deficiency of nitrogen especially in light sandy soils, or a combination of any of these factors.

Iron chlorosis symptoms show up as a yellowing of the upper or younger leaves of the plant and has a marked tendency for the veins and the areas around the veins to remain green. These affected leaves later become cream colored, bronzed, and may even be white. The lower or older leaves may remain green.

Iron chlorosis of azalea is usually the result of the iron in the soil becoming unavailable to the plant with high alkaline soil reaction being the general cause of iron chlorosis of azalea. Other factors may include foundation plantings near copper downspouting, which tend to show this chlorotic condition after a period of time. The iron in this case is tied up by excessive copper in the soil.

To correct this deficiency use: (one of the following)

1. Ferrous Iron Sulfate -- Use at the rate of 1 ounce per 2 gallons of water. Apply directly to the foliage.
2. Chelated Iron (12%) -- Use at the rate of 4 to 8 ounces per 10 gallons of water. Spray directly on the foliage. This material can also be applied to the soil. To get an even distribution, it should be mixed with sand or fertilizer. Water thoroughly after applying.
3. Acidifying Agents -- Where the disease is due to a high alkaline condition, the soil reaction can be changed by the application of sulfur, or iron sulfate to the soil. A soil test should be taken before attempting to change the soil reaction, since azaleas grow best in the ph range of 4.5 to 6.0. The following table will aid in correcting soil reactions.

Table for Acidifying Soils to Desired ph -- Using Sulfur

If using Fe sulfate, use 6 times as much by weight.
*Rates per 100 square feet.