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Chlorosis of Woody Plants

August 1, 2001
Chlorosis is another word for yellowing. Generally with chlorosis of trees, we see yellowing of the foliage, with veins that remain green. If that chlorosis is due to a lack of iron, we call it iron chlorosis. Erroneously, iron chlorosis and chlorosis have become synonymous with too many gardeners. Many Illinois cases may also involve manganese deficiency. As a general rule, iron chlorosis usually causes symptoms most intensely on the newest leaves. Manganese chlorosis symptoms appear on older leaves first.

Chlorosis is a common problem in Illinois on several tree species, including pin oak, sweetgum, maple (especially red and silver), and birch. In most cases, the soil has plenty of macro- and micronutrients for tree growth, but high-pH soils bind up the iron or manganese, making it unavailable to the roots. There is no pathogen involved in this noninfectious problem, although secondary leaf-spotting fungi often invade the weakened tissues. Soil conditions are the cause of the chlorosis.

As chlorosis intensifies, we see brown speckling of the leaves, then totally necrotic leaves, branch tip dieback, and eventually death of branches and even mature trees. The process is a slow one, taking several years before dieback occurs and branches die. Still, if this condition goes untreated, the tree declines and could eventually die. We have had a run of affected pin oaks, red maples, and birches lately at the Plant Clinic. I imagine this is a result of moisture stress, which has compounded the root-absorption problems.

Chlorosis seems to occur when roots grow into an area of high-pH soil. This area could be the foundation of a building, the area under a sidewalk, a gravel parking lot or driveway, or many naturally alkaline sites. This explains why many older trees seem to acquire this problem with age. Logically, any factor that affects root health could aggravate a nutrientabsorption problem. The past several years, we have had an abundance of rain early in the season, often in flooding quantities. Such conditions rob soil of oxygen, causing root injury and inefficient nutrient absorption. Many of the birch trees in my area have chlorosis, but this is because they are in soil that is not conducive to birch growth. Trees with chlorosis may have multiple problems, so look into other possibilities besides the chlorosis. High-pH soil conditions, location of planting, moisture extremes, drainage problems, soil type, competition, compaction, light conditions, and many other site and environmental factors stress root health and may add to the chlorosis problem.

What can be done to remedy the situation? On older trees, there may be nothing we can do to help. Prune out dead wood to avoid secondary wood rots. Try to improve drainage on the site away from the tree. Consider treating the tree for chlorosis and possibly using an acid fertilizer. It might be wise to start with a soil pH test to determine the extent of that problem. There are several types of treatment that can be used for chlorosis. These are discussed in Report on Plant Disease (RPD) no. 603, “Iron Chlorosis of Woody Plants: Cause and Control” or the horticulture fact sheet NC-3-80, “Iron Chlorosis of Woody Plants: Symptoms and Control.” Both publications discuss manganese deficiency as well as iron deficiency. The method you choose will depend on the intensity of the problem, the age of the tree, the pH of the soil, and site restrictions.
Recently, the clinic has received several samples of red maples. Based on the maple samples that we receive at the Plant Clinic, this species seems to have more problems than the other maples. It is not unusual to see dieback and decline in red maple samples with no apparent reason for the decline. The recent samples, however, had yellow to brown interveinal tissues with poor stem growth and overall stunting. These samples were found to be free of infectious disease but were diagnosed with chlorosis due to likely manganese deficiency. The same soil conditions of high pH that inhibit iron uptake can also inhibit manganese uptake. Red maples are particularly sensitive to manganese deficiency. Refer to issue no. 9 (under pin oak problems) for more on chlorosis. Also refer to RPD no. 603.

Author: Nancy Pataky


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