Chlorosis in Trees

Prevent your chlorotic trees from further decline and death. Knowing how to recognize chlorosis in trees and reverse it will help you keep them growing and thriving.

toddsmariettatreeservices.com gathered information on what chlorosis is, its causes, its symptoms, and how to treat it.

What is Chlorosis?

Chlorosis is the paling, lightening, or yellowing of foliage tissue. This condition occurs when a tree’s capacity to manufacture chlorophyll (needed for photosynthesis) is reduced or interrupted. A tree’s foliage can no longer produce the food it requires to grow and thrive when in a chlorotic state.

What Causes Chlorosis?

Foliar chlorosis can occur for several or multiple reasons. The following are among the most common:

Poor Soil Drainage – When the soil retains too much water, it can cause tree roots to stop absorbing vital nutrients. This condition may also lead to root rot and the death of the tree.

Compacted Soil – Foot, mechanical, and vehicular traffic around a tree’s root plate can cause soil compaction. This condition leaves the soil void of oxygen and moisture and generally leads to root and tree death.

Root Damage – When roots are damaged by digging activities or surface roots are damaged by mechanical and/or maintenance equipment, those roots may fail or become diseased. This condition can lead to the rapid decline and death of the tree.

Soil Alkalinity – When soil pH rises above 7.0, the soil becomes alkaline. It can no longer facilitate the absorption of iron and other nutrients required for robust photosynthesis. Ideally, a soil pH of 5.0 to 6.5 should be maintained.

Iron, Manganese, or Zinc Deficiencies – Of these deficiencies, iron is the most common cause of chlorosis. You can determine which of these deficiencies is causing chlorosis by observing which foliage became chlorotic first:

• Iron deficiencies cause younger or terminal leaves to become chlorotic first, then work inward to older or more mature foliage.
• Manganese and zinc deficiencies begin on the older leaves and then move outward.

Insufficient iron availability in the soil is the likely culprit in the absence of other chlorosis causes.

Disease – When a vascular tree disease invades the cambium (xylem and phloem layers beneath the bark), it can rapidly multiply, causing blockages of nutrient flows between the roots and canopy. This reduced transmission of water and nutrients can cause chlorosis, tree decline, and death. Some of those diseases include:

• Dutch Elm Disease
• Verticillium Wilt
• Oak Wilt
• Bacterial Leaf Scorch

These “wilt” diseases cause a tree’s canopy to become chlorotic, then wilted, then necrotic (dead). In many instances, such disease can kill a healthy tree within a single growing season.

Insect Infestation – Boring insects burrow beneath tree bark, creating galleries in the cambium layer or the tree’s heartwood. This activity results in the partial or complete girdling of the tree and/or the introduction of fungi leading to disease. Some of the boring insects responsible for this are:

• Clearwing Borers (day-flying, wasp-like moths)
• Emerald Ash Borer
• Bronze Birch Borer
• Bark Beetle
• Mountain Pine Beetle
• Ambrosia Beetle (named after the fungi it introduces to its host)
• Ips
• Twig Girdlers

Boring insects generally attack trees already in distress or decline. However, when beetle populations are in great numbers, they will attack healthy specimens. When these insects, or the disease they bring, cause enough damage, the tree canopy will first appear chlorotic, then wilted, and finally necrotic.

Note: In many cases, disease and insect infestations move quickly enough to wilt green foliage and kill the tree without showing signs of chlorosis.

Chlorosis Symptoms

Symptoms of chlorosis are generally the same among all tree species. Chlorosis is another way of expressing the yellowing of tree foliage, referring to light green or yellow leaves or needles rather than a healthy dark green. Frequently, leaf veins remain dark green while the rest of the leaf turns a contrasting lighter green or yellow.

Chlorosis Treatments

Many of the following treatments or solutions take time to correct the problem you are experiencing. In some cases, you may have to strongly consider removing the tree to protect the surrounding landscape. When your tree(s) become chlorotic, the following will help you develop a treatment strategy beyond foliar nutrient sprays and other temporary solutions:

Poor Soil Drainage – Most soil drainage issues occur when your soil is disproportionately composed of clay. You can improve soil drainage by:

• Slightly reducing your watering schedule
• Carefully tilling organic material (compost or wood chips) into your soil
• Maintaining fresh mulch around the root plate
• Increasing soil biodiversity by adding earthworms

Note: Tilling sandy soil with your organic material may speed up the betterment of your soil.

Compacted Soil – Even though they occur under different circumstances, compacted soil can be improved using the same treatment used to improve poor soil drainage.

Root Damage – Damaged roots should be cleaned and observed over time. In many cases, roots will compartmentalize damages and recover well. Consider the following:

• If damaged roots soften or become mushy, contact an arborist to evaluate your tree’s health.
• Consider raising the soil level to cover and protect any surface roots.
• If multiple roots have been damaged or severed from digging activities, call a professional to help you take corrective measures (if such measures are possible).

Root damage may require multiple growing seasons for the tree to fully recover. Be vigilant and patient.

Soil Alkalinity – Soil tests can be performed to determine soil pH and nutrient composition. Based on your soil test, you can adjust soil pH by amending agricultural sulfur (powdered sulfur, aluminum sulfate, or iron sulfate) to lower the soil pH, making it more acidic.

Iron, Manganese, or Zinc Deficiencies – Nutrient deficiencies may occur naturally and over time. Such deficiencies can be corrected as follows:

• Fix an iron deficiency by applying a chelated iron fertilizer, in which iron is combined with a chemical called a chelate that helps the iron remain in a plant-deliverable form.
• Fix a Manganese deficiency by liming your soil to the proper pH level for the tree. This is the most practical way to correct and prevent problems with Manganese. Using acid-forming fertilizers in the soil can increase the uptake of this and other essential micronutrients.
• Fix a zinc deficiency by adding zinc to the soil along with compost and/or other organic matter to sandy soil.

Disease – Disease management often requires multi-faceted approaches to help your tree overcome a vascular disease. Since extensive pruning and chemical treatments may be necessary, it is recommended to hire an ISA certified arborist to help you apply specific treatments safely.

Even with the most aggressive treatments, a diseased tree may need to be removed before the responsible pathogen spreads to neighboring trees.

Insect Infestation – Much like disease management, managing insect infestations requires multiple approaches to prevent tree decline and death. Consider the following:

• Set traps to capture adult insects
• Apply insecticides to infested trees coinciding with the pest’s emergence
• Apply chemical deterrents to unaffected trees
• Work to increase the health and vigor of your trees

Note: Treating an insect infestation must include discovering what left the tree weakened, allowing the infestation to occur.

Tip: Boring insect infestations should be communicated to a tree professional immediately. Like the emerald ash borer, many of these insects are closely watched due to their destructive nature and management difficulty.

Tree Foliage Chlorosis

In this article, you discovered information about chlorosis, what causes it in trees, the symptoms to watch for, and how to treat the condition.

By knowing how to identify chlorotic tree foliage, you can take swift action to discover and correct its cause.

You may be allowing disease or infestation to spread unchecked by ignoring chlorosis, resulting in catastrophic widespread tree damage and death.

Sources:
mortonarb.org/trees-plants/tree-and-plant-advice/horticulture-care/chlorosis
forestry.usu.edu/trees-cities-towns/tree-care/preventing-iron-chlorosis
ag.ndsu.edu/publications/lawns-gardens-trees/iron-chlorosis-in-trees
hyg.ipm.illinois.edu/pastpest/200611c.html
web.extension.illinois.edu/focus/index.cfm?problem=chlorosis
entomology.ca.uky.edu/ent43
extension.umd.edu/hgic/topics/root-damage