Chlorosis is a condition where the tree’s ability to manufacture chlorophyll is inhibited. It is usually abiotic, i.e., not caused by living organisms like viruses and fungi. 

Chlorophyll is the green pigment in leaves that plays a crucial role in photosynthesis, making the disease pretty serious and life-threatening. When the leaves are not producing enough pigment, they cannot effectively synthesize energy during photosynthesis. This lack of energy puts the tree in a state of constant decline that often results in death if left unchecked. 

What Causes Chlorosis

Trees can develop chlorosis as a result of several factors, the chief of which is nutrient deficiencies. 

  1. Iron Deficiency

Iron chlorosis is one of the most common forms of chlorosis and occurs when trees cannot absorb enough iron, an important mineral in the formation of chlorophyll. This is common in areas with alkaline soil that have a pH higher than 7.0. 

The soils may contain enough amounts of iron, but the high pH keeps the vital metal in a chemical form that is largely unavailable to plants, resulting in the yellowing of leaves. This yellowing usually starts on the younger leaves and slowly spreads to the older leaves.

Yellowing due to iron deficiency is also interveinal, i.e., it occurs in leaf tissue between the leaf’s veins.  

  1. Magnesium Deficiency

Insufficient magnesium also causes the yellowing of leaves, although leaf tissue may also assume a bronzy-orange color. 

  1.  Potassium Deficiency

Yellowing is similar to that of iron, but this is often accompanied by scorching at the leaf margins and leaf curling. 

  1. Nitrogen Deficiency

Lack of enough nitrogen is typically characterized by the yellowing of older leaves. This is because the tree uses much of the absorbed nitrogen to support new leaf growth, leaving older foliage with little or no nutrients. 

Zinc, sulfur, and manganese deficiencies can also result in chlorosis, with each causing specific leaf-yellowing patterns. Arborists use these patterns to diagnose chlorosis.  

  1. Cultural Causes

The following cultural factors may result in chlorosis;

    •  Overwatering saturates the roots, preventing them from breathing. 
    •  Damaged roots that cannot absorb enough water, nutrients, and oxygen often cause the yellowing of leaves. 
  • Restricted root growth, especially in urban areas due to obstacles like building foundations, streets, and pavements. The roots are usually shallow, with limited access to nutrients, water, and air. 
  • Compacted soils are also difficult for roots to penetrate

Tree Species Affected

Any tree can suffer from chlorosis if the conditions are right. However, some tree and shrub species are more susceptible to the disease than others. These include those sensitive to soils with high pH like pin oak, sweetgum, flowering dogwood, white oak, silver maple, magnolia, catalpa, and tulip tree.

Avoid these types of trees when planting in soils with high pH levels. 

Symptoms of Chlorosis

Yellowing of leaves is the main symptom of chlorosis. This typically begins with leaf tissue assuming a lighter green to lime green color, with the leaves becoming more yellow as the condition gets serious.

The pattern of yellowing will depend on the primary cause of the disease.

Consequences if Left Untreated

Yellow leaves cannot perform photosynthesis effectively, and thus, the tree is pretty much starving. Such trees are weak, with stunted growth, and leaving them unattended often kills the plant. 

Also, trees suffering from chlorosis do your lawn aesthetics little justice; yellow leaves are an ugly feature in seasons other than fall.  

Treatment  

The method of treatment varies depending on the cause of the condition. 

If it is due to poor soil conditions like compaction in urban areas, cultural practices like mulching help provide a more favorable environment.   

If the cause is caused by excess water in the soil, adjust your watering habits, so the ground doesn’t remain saturated for too long. Do your watering slowly to moisten the soil deep enough for the tree roots without saturating it with too much water. 

Contact your arborist to check if damaged or constricted roots are responsible for your tree’s chlorosis. Depending on the extent of the problem, they may be able to correct these problems and save the tree.

 Nutrient deficiencies can be treated in the following ways; 

  • Foliar application: This involves applying nutrients in a chelate or water-soluble form to correct the problem. The technique only affects leaves present during the application, and thus, several treatments may be necessary per growing season to keep the foliage green. 
  • Soil treatment: Your arborist will take a soil test to determine the pH and availability/lack of nutrients. Depending on the results, they perform specific procedures to add nutrients or correct the pH by acidifying the soil. 
  • Trunk application: This method involves applying deficient nutrients directly to the tree via the trunk. There are several ways to go about it, and all should be performed by a trained arborist as it may wound the trunk of an already vulnerable tree. 

 

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