Leaf scorch is a condition that is typically caused by unfavorable environmental conditions.
This type of leaf scorch is not contagious, and no chemical or other product will effectively treat the condition. In fact, simple leaf scorch may be caused by excessive amounts of chemical fertilizer.
Other causes include too little water, too much sun, harsh winds, etc., which all have the effect of drying leaves.
Typically, leaf scorch appears as dry spots or burns along the margins of leaves. These damaged leaves may fall from the affected plant, shrub, or tree.
In this article, we discuss and describe leaf scorch and provide sound advice on establishing good management practices to prevent it. Read on to learn more.
MU Extension Integrated Pest Management: Leaf Scorch
Leaf Scorch Is Naturally Present In The Heat Of The Summer
The hot summer sun naturally dries out vegetation, so you are very likely to see leaf scorch on all sorts of plants, grasses, shrubs, and trees during the hottest days of summer.
No matter what sort of foliage a plant has, leaves or needles, this condition is referred to as a “leaf” scorch, and it is caused by the plant’s inability to access the water it needs to survive in hot, harsh weather.
Leaf scorch will initially manifest as dry, brown leaf margins. If intervention (in the form of shade and water) is not provided, the leaf tissue between the veins may also dry out and turn brown. Eventually, entire leaves will dry and fall.
Leaf scorch can happen to any plant, but it is very likely to occur in trees (e.g., Aspens) with large, thin leaves that dry out easily.
In very severe circumstances, trees that have needles (e.g., evergreens) may also develop leaf scorch. When this happens, the tips of the needles turn pink and light tan. Without intervention, the needles will become completely brown and will fall.
This phenomenon is known as Kladoptosis (aka Cladoptosis), and it can affect the leaves and twigs of plants, shrubs, and trees subjected to stress.
During drought or other stressful conditions, the plant is stimulated to produce ethylene gas which causes a layer of separation at the base of the plant’s leaves and sometimes twigs.
Plants do this as a defense mechanism that allows them to shed tissue that is not entirely necessary to preserve the plants’ roots so that the plant can grow again when conditions improve.
During Kladoptosis, the plants’ leaves may turn yellow and fall like autumn. This is very common among Willow trees, Cottonwoods and Aspens.
Why Do Leaf Edges Brown First?
Plants take up water through fine feeder roots. The water is then transported through the plant’s vascular system to the plant’s leaves, needles, or other foliage.
The water rises through the plants’ veins and supplies the tissue nearest to the plant’s central stem or trunk first.
The edges of leaves and the tips of needles are furthest away from the central stem or trunk, so they may get left out without insufficient water. Hence, scorched leaf tips and margins can initially identify leaf scorch.
Is Leaf Scorch Always Caused By Lack Of Water?
Sometimes, there may be plenty of water present, but a plant that cannot make good use of that water may suffer from leaf scorch.
For example, leaf scorch may result if the plants’ root system is not adequate to meet the plant’s needs.
There are several reasons why this might happen, such as:
- A plant or tree growing in an area that is hemmed in by pavement may not be able to develop a healthy root system.
- A plant or tree growing in an area subject to heavy tilling or other disturbances may experience root damage or loss that leaves the root system weakened and inadequate.
- Damage to the plant’s roots caused by incorrect planting depth or girdling will cause leaf scorch and drop.
- Chemicals (e.g., soil sterilant or road salt) applied in the plant or tree’s vicinity may cause root damage or loss.
- Excessive amounts of fertilizer may cause chemical damage (burns) to the plants’ root system.
- Using fertilizer spikes that deliver a lot of salty fertilizer chemicals to a small area may cause leaf scorch on one part of the plant or tree.
- Damage to the plant’s limbs and stems may simply prevent water from being transported to parts of the plant or tree.
- Dry weather during the plants’ dormant period may result in leaf scorch during growth.
- Overwatering for an extended period can also cause leaf scorch because waterlogged plants and trees may not be able to grow fresh, new roots that can absorb water. Root scorch may occur when root growth and development are thwarted by soggy soil. This is especially true if the plant has been deprived of water during its dormant time.
Excessive Heat Causes Leaf Scorch And Stress
Heat-related leaf scorch is often accompanied by heat stress. Other signs and symptoms to watch for in plants and trees in very hot environments and/or during drought include discolored leaves, drying out, and damage to the soil line.
It’s important to note that these heat-related symptoms are not always caused by heat-related to the weather.
You may have perfectly lovely weather yet still see these symptoms in plants subjected to less-than-ideal conditions and treatment. For example:
- A plant, shrub, or tree planted close to the west or south side of a fence or building may receive a great deal of reflected heat which will cause leaf scorch and heat stress symptoms even if its care is otherwise excellent.
- Plants, shrubs, and trees that are surrounded by rock mulch may be exposed to a great deal of absorbed heat at the root level, as well as reflected heat, especially if the rock is dark in color.
- Black plastic mulch also absorbs and reflects a vast amount of heat that may kill the plants intended to protect.
- Black plastic containers absorb and hold a great deal of heat. This may cause damage or death to roots and result in leaf scorch.
Bacterial Leaf Scorch – Garden Notes
Bacterial Infection Can Cause Leaf Scorch
Although, more often than not, leaf scorch is caused by inhospitable environmental conditions or improper care, it is also possible for this condition to be caused by the bacteria, Xylella fastidiosa (Zy-lel-uh fas-tid-ee-OH-suh).
This infection is very common among shade trees with large, thin, permeable leaves.
Examples include:
- Sweet Gum
- Hackberry
- Sycamore
- Mulberry
- Catalpa
- Ginkgo
- Maple
- Elm
- Oak
It is possible for trees affected by this pathogen to die of the infection. The bacterium causes leaf scorch by inhabiting the plant’s vascular system and blocking water movement from the plant’s roots. Watch for these signs of (BLS):
Signs Of Bacterial Leaf Scorch
- Watch for the presence of plant hoppers (e.g., spittlebugs, treehoppers, sharpshooters) that feed on infected plants and then carry the bacterium to healthy plants.
- In some types of trees, the brown scorched areas may be surrounded by a yellow border.
- Signs of leaf discoloration and scorch start at the crown (top) of the tree.
- Affected plants’ growth is stunted, and affected areas die back.
- Symptoms return every year and spread progressively.
It can be hard to pinpoint Bacterial Leaf Scorch (BLS), even in trees that display these symptoms, because these can also be symptoms of environmental stress, root disease, and drought.
Difference Between BLS and Drought Stress
Look for these telltale signs of drought stress to tell the difference:
- If the scorching is caused by drought, the symptoms will be uniform throughout the plant, shrub, or tree. They will not begin at the crown or on new, young growth.
- With drought scorching, you’ll notice dry leaf tips and then margins starting on interior leaves and then spreading throughout the foliage.
- Drought scorching usually starts in mid-to-late summer.
Sadly, there is no treatment for BLS, but some trees can be kept alive and doing fairly well with attentive pruning to promptly remove any affected branches.
Hiring a licensed arborist to provide antibiotic trunk injections to very valuable trees is also possible. This will help keep symptoms under control, but it is not a cure.
Bacterial Leaf Scorch
Prevention Is The Best Medicine For Leaf Scorch
No matter the cause of your leaf scorch problem, once it has occurred, you will not be able to undo it quickly.
Plants, shrubs, and trees suffering from leaf scorch will need good pruning and correction of the stressors that caused the condition.
Familiarize yourself with the needs of your plants and take steps to provide the right amount of water, light, and nourishment. Pay close attention to soil conditions.
For the most part, light, airy, well-draining soil that can retain just the right amount of moisture and provide good air circulation to the roots is always a good foundation for healthy plants.
Adjust your watering habits so your plants do not dry out entirely during the winter. Outdoor plants and large, mature trees in areas that do not have snow cover will benefit from a deep monthly soaking.
For winter watering, choose a day above freezing temperature in the morning. You should water in the morning so that the water can soak in before temperatures drop overnight.
If a sheet of ice freezes on the surface of the soil, plant roots will suffocate, and that will cause leaf scorch when spring comes.
Practice soak-and-dry watering with garden plants, shrubs, and trees throughout the growing season. Allow the top few inches of soil to dry before providing a deep watering. This will ensure that the plants’ roots can breathe.
Even if your plants experience some leaf scorch during very hot, dry weather, don’t overwater. Keep up a consistent schedule of deep, infrequent watering.
Remember that your lawn may need more water than is healthy for your flowerbeds, veggie garden, and landscaping. Tailor your watering habits to suit the targeted plants.
Best Garden Practices Help Prevent Leaf Scorch
Leaf scorch is a common condition caused by various factors, including unfavorable environmental conditions, improper care, and sometimes bacterial infection.
Although it cannot be treated with chemicals or products, prevention is key to managing leaf scorch effectively.
Proper watering practices, including deep soak-and-dry watering, can help maintain healthy root systems and prevent leaf scorch.
Additionally, avoiding heat stress caused by reflected or absorbed heat is essential in maintaining the well-being of plants, shrubs, and trees.
For trees afflicted with BLS, attentive pruning and, in some cases, antibiotic trunk injections by a licensed arborist can help manage symptoms.
In the final analysis, understanding and meeting the specific needs of plants and maintaining proper soil conditions are vital for preventing and treating leaf scorch effectively.
Gary Antosh
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