Leaf burn is a condition that is usually caused by adverse environmental conditions.
This type of leaf burn is not contagious and no chemical or other product will effectively treat this condition. In fact, simply burning the leaves can be caused by excessive amounts of chemical fertilizer.
Other causes include too little water, too much sun, strong wind, etc., all of which have the effect of drying the leaves.
Usually, leaf scorch appears as dry spots or burns along the edges of the leaves. These damaged leaves may fall from the affected plant, shrub or tree.
In this article, we discuss and describe leaf scorch and share tips on establishing good management practices to prevent it. Read on to find out more.
Scorch is naturally present in the heat of summer
The hot summer sun naturally dries out vegetation, so you’re likely to see burns on all kinds of plants, grasses, shrubs and trees during the hottest days of summer.
Regardless of what type of foliage a plant has, leaves or needles, this condition is called “leaf scorch,” and is caused by the plant’s inability to access the water it needs to survive in hot, harsh weather.
Leaf burn will initially manifest as dry, brown leaf edges. 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 all the leaves will dry up and fall off.
Leaf burn can occur on any plant, but is most likely to occur on trees (eg, Aspens) with large, thin leaves that dry out easily.
In very severe circumstances, trees that have needles (eg evergreens) can also develop leaf burn. When this happens, the tips of the needles turn pink and bright yellow. Without intervention, the needles will turn completely brown and fall off.
This phenomenon is known as cladoptosis (also known as cladoptosis), and it can affect the leaves and twigs of stressed plants, shrubs and trees.
During drought or other stressful conditions, the plant is stimulated to produce ethylene gas which causes a separation layer at the base of the plant’s leaves and sometimes the twigs.
Plants do this as a defense mechanism that allows them to discard tissue that is not completely necessary to preserve the plant’s roots so that the plant can grow again when conditions improve.
During cladoptosis, plant leaves may turn yellow and fall like autumn. This is very common among willow, cottonwood and aspen trees.
Why are the edges of the leaves first brown?
Plants take up water through fine feeder roots. The water is then transported through the vascular system of the plant to the leaves, needles or other foliage of the plant.
Water rises through the veins of plants and first supplies the tissue closest to the central stem or trunk of the plant.
The edges of the leaves and the tips of the needles are the furthest from the central stem or trunk, so they can be absent without sufficient water. Therefore, scorched leaf tips and edges can initially identify leaf burn.
MU Extension Integrated Pest Management: Leaf Scorch
Is leaf burn always caused by lack of water?
Sometimes there can be plenty of water, but a plant that can’t use that water well can suffer from leaf burn.
For example, leaf scorch can occur if the plant’s root system is not adequate to meet the plant’s needs.
There are several reasons why this can happen, such as:
- A plant or tree growing in an area bordered by pavement may not be able to develop a healthy root system.
- A plant or tree growing in an area subject to heavy tillage or other disturbances may experience root damage or loss causing the root system to be weakened and inadequate.
- Damage to plant roots caused by improper planting depth or girdling will cause burns and leaf drop.
- Chemicals (eg, soil sterilant or road salt) applied near a plant or tree can cause root damage or loss.
- Excessive amounts of fertilizer can cause chemical damage (burns) to the root system of plants.
- Using fertilizer spikes that deliver a lot of salty fertilizer chemicals to a small area can cause leaf burn on one part of the plant or tree.
- Damage to plant limbs and stems can simply prevent the transport of water to parts of the plant or tree.
- Dry weather during the plant’s dormant period can lead to leaf scorch during growth.
- Overwatering over a long period of time can also cause leaf burn because flooded plants and trees may not be able to grow fresh, new roots that can absorb the water. Root burn can occur when root growth and development is inhibited by wet soil. This is especially true if the plant has been deprived of water during the dormant period.
Excessive heat causes leaf burn and stress
Heat-induced leaf burns are 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, desiccation, and damage to the soil line.
It is important to note that these heat-related symptoms are not always caused by weather-related heat.
You may have perfectly fine weather, but still see these symptoms in plants that are subjected to less than ideal conditions and treatments. For example:
- A plant, shrub or tree planted near the west or south side of a fence or building can receive a large amount of reflected heat that will cause leaf burn and heat stress symptoms even if its care is otherwise excellent.
- Plants, shrubs and trees surrounded by stone mulch can be exposed to a large amount of absorbed heat at the root level as well as reflected heat, especially if the stone is dark in color.
- Black plastic mulch also absorbs and reflects a tremendous amount of heat that can kill the plants it is intended to protect.
- Black plastic containers absorb and retain a large amount of heat. This can cause root damage or death and lead to leaf burn.
Bacterial leaf burn – garden notes
Bacterial infection can cause leaf scorch
Although, most often, leaf burn is caused by inhospitable environmental conditions or improper care, it is possible that this condition is also caused by the bacterium 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 that trees affected by this pathogen die from the infection. The bacterium causes leaf burn by colonizing the plant’s vascular system and blocking the movement of water from the plant’s roots. Watch for these signs (BLS):
Signs of bacterial leaf blight
- Watch for the presence of plant hoppers (e.g. spitters, leafhoppers, arrowroots) that feed on infected plants and then transmit the bacteria to healthy plants.
- In some tree species, brown burnt areas may be surrounded by a yellow border.
- Signs of leaf discoloration and burns begin at the crown (top) of the tree.
- The growth of the affected plants slows down, and the affected areas die.
- Symptoms return every year and progressively spread.
Bacterial leaf blight (BLS) can be difficult to determine, even on trees that show these symptoms, because they 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 see the difference:
- If the burn is caused by drought, the symptoms will be uniform throughout the plant, bush or tree. It will not start in the crown or on new, young growth.
- With dry burn, you will notice dry tips of the leaves and then edges that start on the inner leaves and then spread throughout the leaves.
- Drought usually begins in mid to late summer.
Unfortunately, there is no treatment for BLS, but some trees can be kept alive and do quite well with careful pruning to immediately remove any affected branches.
It is also possible to hire a licensed arborist to administer antibiotics to the trunk of very valuable trees. This will help keep the symptoms under control, but it is not a cure.
Bacterial leaf scorch
Prevention is the best cure for leaf burn
Regardless of the cause of your leaf burn problem, once it happens, you won’t be able to reverse it quickly.
Plants, shrubs and trees suffering from leaf burn 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 nutrition. Pay special attention to soil conditions.
In general, a light, airy, well-draining soil that can hold the right amount of moisture and ensure good air circulation to the roots is always a good foundation for healthy plants.
Adjust your watering habits so your plants don’t dry out completely during the winter. Outdoor plants and large, mature trees in areas that do not have snow cover will benefit from a deep monthly soak.
For winter watering, choose a day above freezing in the morning. You should water in the morning so that the water can be absorbed before the temperature drops overnight.
If a sheet of ice freezes on the surface of the soil, plant roots will suffocate, which will cause leaf burn when spring arrives.
Practice soaking and dry watering with garden plants, shrubs and trees throughout the growing season. Allow the top few inches of soil to dry out before watering deeply. This will ensure that the roots of the plants can breathe.
Even if your plants experience leaf burn during very hot and dry weather, do not overwater. Maintain a consistent deep, infrequent watering schedule.
Remember that your lawn may need more water than is healthy for your flower beds, vegetable garden and landscaping. Adjust your watering habits to suit your target plants.
Best gardening practices help prevent leaf burn
Leaf burn is a common condition caused by a variety of factors, including adverse environmental conditions, improper care, and sometimes bacterial infection.
Although it cannot be treated with chemicals or products, prevention is key to effectively managing leaf burn.
Proper watering practices, including deep watering and drying, can help maintain a healthy root system and prevent leaf burn.
In addition, avoiding heat stress caused by reflected or absorbed heat is essential to maintaining the well-being of plants, shrubs and trees.
For trees affected by BLS, careful pruning and, in some cases, injections of antibiotics into the trunk by a licensed arborist can help manage symptoms.
In the final analysis, understanding and meeting the specific needs of plants and maintaining appropriate soil conditions are vital to the prevention and effective treatment of leaf burn.