Chlorosis

An Abiotic Problem Of Shade Trees

Chlorosis is a common problem of shade trees growing in the urban areas of Minnesota. Oaks tend to be highly susceptible, but many other tree species including maples and birch also suffer from this disorder. This is a chronic condition which slowly decreases a tree’s overall vigor and ability to survive.

Chlorosis is the suspension of chlorophyll formation in leaves. (Chlorophyll is the green pigment essential in photosynthesis.) The most visible symptom of chlorosis is a general yellowing or pale green coloring of the foliage. As the condition worsens leaves lose their capacity to capture light energy used to manufacture sugars
used as food.

Cause
A tree’s chlorophyll production may be compromised by a deficiency of elements like iron, manganese, zinc, or copper. The availability of these micronutrients in soil and the plant’s absorption capability is reduced when soil nutrient exchange capacity is limited by soil pH.

Additional contributors to the formation of chlorosis may include root damage, poor drainage, and high soil alkalinity (pH >7.0).

In some cases only a portion of the tree may exhibit chlorotic symptoms. Before implementing any restorative treatments, a soil analysis and evaluation is necessary.

Management
Prevention is the best control for chlorosis. Do not plant trees which are susceptible , such as Eastern pin oaks, in soils with a pH above 7.0 or in soils low in organic matter.

Cause	Recommended Treatment
High soil pH *	Add Prescription Organic Matter©, Elemental Sulfur, micronutrient injections
Lack of micronutrients*	Apply micronutrient fertilizer & Prescription Organic Matter
Stem girdling roots	Assess with root collar excavation & apply Root Enhancement©
Construction damage	Treat with Cambistat® (tree growth regulator) & Root Enhancement
Limestone/ rock mulch	Remove limestone mulch and apply Root Enhancement
Compacted soils*	Perform root collar excavation & Root Enhancement
Low soil nutrients*	Apply Prescription Organic Matter & booster fertilizer
Trunk girdling (twine)	Remove twine, may be necessary to replace tree
Excessive water	Reduce moisture, increase drainage, add Prescription Organic Matter

*Soil testing necessary.
Some processes may require repeating an indeterminate number of times in order to facilitate tree health.

Specific measurements of foliage and soil nutrients and pH are necessary to provide successful treatment of chlorosis. If the problem is related to high soil pH, restoration of leaf color can be accomplished and maintained for several years using elemental sulfur and Prescription Organic Matter. The goal is to lower soil pH below 6.5. Iron may also be injected directly into the tree to provide a more immediate result.

If possible use a soil acidifier (Miracid) when irrigating sensitive plants. (Municipal water systems tend to be alkaline.) Do not use lime under the canopy of shade trees, as lime raises the pH of soil. Mulching the area around trees with prescription organic matter with wood chips or shredded bark will yield best results. Avoid limestone rock mulches that can raise the soil pH.

During construction projects try to avoid damaging tree roots. A tree growth regulator, Cambistat can reduce chlorosis on mature trees affected by construction. The growth regulator enhances the growth of roots damaged by construction and reduces the overall nutritional needs of the tree by reducing above ground growth. For long-term benefit it is best to utilize Cambistat in conjunction with other soil and root enhancement systems.