- Bacterial Leaf Scorch on Oaks
- Treating Bacterial Leaf Scorch
- Bacterial leaf scorch
- Bacterial Leaf Scorch Diagnostic Guide
- Treatment Expectations
- AgriFoodGateway Horticulture International
- Bacterial Leaf Scorch – Trees
- Management of bacterial leaf scorch
- Additional Resource
- Bacterial leaf scorch of blueberry
- Notifiable status
- Host range
- Actions to minimise risk
- Bacterial Leaf Scorch
Bacterial Leaf Scorch on Oaks
COMMON NAME: Bacterial Leaf Scorch (BLS) on Oak
SCIENTIFIC NAME: Xylella fastidiosa subsp. multiplex
Oak is one of five other crops or landscape plants that are susceptible to X. fastidiosa subsp. multiplex. BLS is a common disease of oaks in Texas, in part due to the climatic extreme of hot and dry spells.
SYMPTOMS: Typical symptoms of BLS on oaks include premature browning, or scorching of leaves often accompanied by a yellow border separating the green and brown tissue. As premature leaf abscission occurs the tree will eventually die, usually within 4 – 5 years of the initial appearance of symptoms. BLS usually appears randomly distributed when present in a population of oak trees.
BIOLOGY: A variety of oaks including live, southern red, and bur are very susceptible to this disease. This pathogen is primarily spread by insect vectors such as spittlebugs and leafhoppers that also feed on other woody species where the pathogen may be further transmitted. Once introduced the bacteria lives in the xylem, plugging essential tissue carrying water and nutrients.
MANAGEMENT METHODS: Proper nutritional and water requirements should be met for oak trees. Correct diagnosis is crucial as bacterial leaf scorch can often be confused with symptoms exhibited by abiotic stresses and oak wilt. Affected branches should be immediately removed and pruning tools sanitized.
For pathogen, species affected, alternate hosts, biology, and management methods refer to:
For symptoms and management methods refer to:
This factsheet is authored by Zachary Howard (Masters student)
Factsheet information for the plant health issues represented by the images on the 2019 TPDDL calendar were written by graduate students enrolled in the Department of Plant Pathology & Microbiology PLPA601 Introductory Plant Pathology course in the 2018 Fall semester (course instructor: Dr. David Appel). This exercise provides an opportunity for a high impact learning activity where the students are tasked with producing an informational output directed to the general public and to provide opportunity for the students to write.
Photo credits: John Hartman, University of Kentucky, Bugwood.org
Treating Bacterial Leaf Scorch
Bacterial leaf scorch (BLS) is caused by the bacterium Xylella fastidiosa. This disease impacts certain shade trees resulting in uneven ‘scorching’ of leaf margins in late summer and early fall. The bacteria themselves live in the xylem tissue and gather in clusters called biofilms. These ‘bunches’ of bacteria clog the xylem and block water transport, which leads to the scorch symptoms.
Scorching of leaf margins caused by bacteria.
The disease typically progresses throughout the tree for up to a decade causing so much dieback that the tree eventually dies. Symptoms and damage are usually most visible on pin and red oaks, but shingle, bur and white oak can be affected as well. Additionally, BLS can infect elm, sycamore, mulberry, sweetgum, sugar maple, and red maple. There are also numerous asymptomatic hosts.
Xylem-feeding leafhoppers and spittlebugs spread the bacterium from one tree to another. BLS is sometimes mistaken for other leaf diseases, or for drought and heat stress. The unique late summer development of BLS symptoms is the defining characteristic.
Thanks to recent advances in DNA analysis, BLS can now be detected at any time of the year, not only when symptoms appear late in the growing season. This allows an arborist to determine well in advance if a tree requires treatment. Experience at Bartlett Tree Experts has shown that BLS can often be effectively suppressed for many years if the tree is treated and provided with good cultural care, especially if the disease is detected early.
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Bacterial leaf scorch
Red oak with BLS symptoms
Photo credit: Bugwood.org
Bacterial leaf scorch is caused by the bacterium, Xylella fastidiosa. This bacterium is limited to the xylem of infected hosts and is transmitted by xylem-feeding insects such as leafhoppers, sharpshooters and spittlebugs. The pathogen disrupts vascular function and, as a result, damage that is similar to drought damage begins to appear in mid-summer. Infected trees display leaves with scorching symptoms – including marginal necrosis and chlorosis. Leaves may eventually become completely brown and remain attached. Chronic infection can lead to stunting, dieback and witch’s brooms. The host range is very wide, but the disease is most commonly observed in Florida on oaks (especially turkey oak), sycamore, sweetgum and elms. Control is not common on trees, but anti-biotic injections can be useful.
|Identifying the injury:||Foliage with marginal chlorosis, followed by necrosis. The necrosis is usually closer to the leaf margins. Leaves turn completely brown. Stunting, dieback and sometimes tree death.|
|Identifying the pathogen:||X. fastidiosa is a microscopic rod-shaped bacterium that is not easily cultured on artificial media.|
|Susceptible trees:||Wide host range including: oaks (especially laurel and turkey oak), sycamore, sweetgum and elms.|
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- Wikipedia – Bacterial Leaf Scorch
- American Phytopathological Society – Bacterial leaf scorch (BLS) of shade trees
Bacterial Leaf Scorch Diagnostic Guide
Bacterial leaf scorch has no known cure. A variety of management practices can successfully extend the longevity of infected trees. These include treatment with antibiotics and water stress reduction through mulching, irrigation, and growth regulation. These management practices are very successful, however, annual treatments with antibiotics are needed to keep this disease suppressed and the tree alive.
Other Treatment Practices
- Bacastat should be included with other sound cultural practices such as mulching, supplemental irrigation during dry periods, and other insect and disease management practices.
- Macro-infusion treatments have performed equally as well as micro-infusion treatments.
- BLS is included on the Cambistat label. Results with Cambistat as a stand-alone treatment for bacterial leaf scorch have been variable.
Mulching The Root System and Irrigating
Mulch is not a direct treatment for an infected tree, nor will it prevent infection. It will however create optimal conditions for the root system to be its healthiest. A healthier tree will fare better as this chronic disease takes its toll. Apply 2-4 inches of organic mulch out to the dripline of the tree and beyond if possible.
Bacterial leaf scorch symptoms can be more severe if shade trees are stressed due a lack of soil moisture. Trees infected with bacterial leaf scorch have reduced capacity to transport water because Xylella clogs the conductive vessels of the tree. Proper watering during dry periods is also crucial since the primary injury from this disease is desiccation. Proper watering for a mature tree means watering deeply (2 hours) every couple of weeks.
Antibiotic treatments using Bacastat suppresses the growth of the bacteria and can significantly reduce bacteria levels and leaf scorch symptoms. This treatment is appropriate only on trees that are infected with bacterial leaf scorch. Bacastat will provide suppression for one growing season and requires annual application.
Bacastat is applied by Micro-infusion. Small holes are drilled in the root flare of the tree, and Bacastat is infused directly into the water conducting tissue. The active ingredient in Bacastat is completely water soluble and causes less damage at the injection site compared to solvent-based products.
Methods of Increasing Leaf Water Retention
The tree growth regulator CambistatTM can be applied to trees to increase their ability to withstand certain environmental stresses such as drought. Cambistat works by shifting some of the energy that a tree would allocate to shoot growth towards the production of fibrous roots and defense compounds. Cambistat causes the tree to produce thicker leaves and increased protective hair-like structures on the surface of leaves, which reduce water loss from the tree. While CambistatTM does not directly inhibit bacterial growth, the prevention of water loss can significantly reduce water stress, which plays a significant role in the development and severity of this disease. Cambistat has shown promising results when used as a stand alone treatment on trees.
Inhibiting Disease Transmission
Xytect and not directly effective against Xylella but it may prevent the spread of Xylella to nearby healthy trees. One additional benefit of using Xytect is that it protects the tree from many opportunistic insects, especially wood feeding borers. These insects are deadly, and are attracted to stressed trees. The presence of Xytect in the trees vascular tissue will keep these destructive insects out. Xytect needs to be applied annually and one treatment will last a full season.
Relative to total sales, blueberries are the number one fruit commodity in the state of Georgia, surpassing even peaches. Recently, a new disease has been identified in the Georgia blueberry production region. This disease has been named “bacterial leaf scorch,” and it is caused by the bacterium Xylella fastidiosa.
Through initial field surveys conducted in the summer of 2007, it was determined that this disease has the potential to become a major threat to blueberry production in Georgia and elsewhere, especially in the southern highbush blueberry varieties. Among these varieties, ‘FL8619’ (alias ‘V1’) has proven to be the most susceptible. However, ‘Star’ and other varieties are also showing substantial disease incidence and severity in several locations. At this early stage, little is known for sure about the epidemiology (means of dissemination and spread) of this disease, and the basic research to determine the means of spread and interaction within the south Georgia environment needs to be completed. In addition, research-based control methods need to be established for this disease. Current recommendations are based on information derived from other plant systems, such as wine grapes, and information needs to be developed specifically for blueberries.
- Causal organism
- Disease cycle and causal conditions
- Chemical controls
Authors: Phillip M. Brannen Authors: Gerard Krewer Authors: Bob Boland Authors: Dan Horton Authors: CJ Chang Publisher: University of Georgia Extension Year: 2016
Bacterial Leaf Scorch – Trees
Bacterial leaf scorch on oak tree – credit: J. Sherald US Dept. Interior, NPS
Bacterial leaf scorch is a disease of shade trees in Maryland. It affects a large number of shade trees including elm, catalpa, hackberry, gingko, oak, sycamore, maple, mulberry, and sweetgum in the landscape. Depending on the severity, this disease can cause tree death.
The pathogen is a bacterium that grows inside the plant’s vascular tissue where it blocks water movement from the roots. The organism, Xylella fastidiosa, is a small gram negative bacterium with no flagella. It doesn’t form resting spores, has a thick rippled cell wall, and does not grow on conventional bacteriological media. This bacterium is spread by plant hoppers called sharpshooters, treehoppers and spittlebugs that feed on infected plants and after feeding, the bacterium will spread systemically through the vascular system. Symptoms typically appear in mid to late summer on lower branches as irregular marginal browning on interior leaves. Symptoms progress along the branch towards the tip.
Symptoms will occur every year and progress through the crown. Scorched areas may have a yellow halo around them depending on the tree species. Reduced growth and dieback are also common in severely infected plants. These symptoms are sometimes mistaken for drought, environmental stress, or root diseases.
Bacterial scorch symptoms differ from drought scorch symptoms, in that they appear first on the lower branches and on the older interior leaves. Drought scorch symptoms will be more uniform and will first appear near the upper branches and on the younger leaves near the tips of the branches.
Bacterial leaf scorch symptoms on elm
Bacterial leaf scorch symptoms on sycamore
Bacterial leaf scorch symptoms on maple leaves
Management of bacterial leaf scorch
There are no treatments for bacterial leaf scorch. However, infected trees may continue to persist in the landscape if symptomatic branches and dead wood is pruned out promptly. Antibiotic trunk injections have shown promise but they only relieve symptoms and don’t provide a cure.
Bacterial leaf scorch of blueberry
Bacterial leaf scorch of blueberry (Xylella fastidiosa) is an exotic plant pest not present in Australia. This disease is a serious threat to Australia’s blueberry industry.
Bacterial leaf scorch of blueberry is caused by the bacterium Xylella fastidiosa. The bacterium lives and multiplies in the sap, blocking water uptake to the leaves.
Sap feeding insects spread the disease between plants. Once a plant is infected there is no treatment but to destroy infected plants in an attempt to minimise spread.
Xylella fastidiosa is responsible for a number of diseases in other horticultural crops, including Pierce’s disease of grapevine, citrus variegated chlorosis and alfalfa dwarf disease. No strains of Xylella fastidiosa are present in Australia.
Bacterial leaf scorch of blueberry (Xylella fastidiosa) is a notifiable plant disease in NSW.
All notifiable plant pests and diseases must be reported within 1 working day. You can report notifiable plant pests and diseases by one of the following methods:
- Call the Exotic Plant Pest Hotline 1800 084 881
- Email [email protected] with a clear photo and your contact details
- Complete an online form
A full list of notifiable plant pests and diseases can be found in Schedule 2 of the NSW Biosecurity Act 2015.
Bacterial leaf scorch symptoms first appear with the tips or edges of leaves developing a burnt appearance along the leaf margin.
The ‘burnt’ edge of the leaf progresses unevenly towards the mid rib with a fairly distinct line between the dead part of the leaf and the inner green tissues (Figure 1).
Infected leaves drop from the bush and young stems may turn yellow. Once the leaves have dropped, the plant takes on a skeleton-like appearance (Figure 2) and eventually dies.
The presence of bacteria in the plant sap restricts flow of water and nutrients in the plant. Infected plants become stunted and less productive. Leaves die and flowering becomes irregular.
Even some symptomless cultivars, known to be infected with the disease but otherwise showing no outward sign of infection, have displayed significant yield losses in comparison to plants known to be free of Xylella fastidiosa.
There is no known treatment for bacterial leaf scorch once plants become infected. Susceptible plants will eventually die, however they may still survive for a few years if disease spread and plant decline is slow.
To date, the Xylella fastidiosa strain impacting blueberries is known to be hosted by both southern highbush and rabbiteye varieties. Some cultivars appear to be resistant to or tolerant to the disease, though these resistant or tolerant cultivars can still act as sources of inoculum for disease spread.
Many common weeds and grains including bermudagrass, rye, fescue grasses, watergrass, blackberry, elderberry, cocklebur, and nettle are known hosts of strains of Xylella fastidiosa. Overseas, common orchard weeds such as bluegrass, burclover, cheeseweed, chickweed, filaree, London rocket, and shepherd’s purse have also been found to be infected.
Xylella fastidiosa bacteria are carried in the sap of host plants and can be spread between plants by grafting, pruning or sap feeding insect vectors.
The most efficient known vector is the glassy winged sharpshooter (Figure 3). Glassy winged sharpshooter is not currently found in Australia though it is possible that natural insect vectors of this disease may already exist in Australia.
Introduction of Xylella fastidiosa to Australia could occur with human assisted movement of infected plant material or with insect vectors. The disease is not carried on or spread by seeds.
Xylella fastidiosa is native to the Americas and has spread to Europe where there have been detections in Italy, France and the Netherlands. It is also present in the Caribbean, Taiwan, Iran, Turkey, Lebanon, Kosovo and India.
The particular strain of Xylella fastidiosa affecting blueberries is thought to be a unique recombinant strain that has been well documented in the United States. However, reports indicate that other strains could also potentially infect and cause symptoms in blueberry.
Actions to minimise risk
Put in place biosecurity best practice actions to prevent entry, establishment and spread of pests and diseases:
- practice “Come clean, Go clean”
- ensure all staff and visitors are instructed in and adhere to your business management hygiene requirements
- source propagation material of a known high health status from reputable suppliers
- monitor your plants regularly
- keep records
Bacterial Leaf Scorch
Bacterial leaf scorch is sometimes abbreviated as BLS and can also be referred to as marginal leaf burn. This issue affects plants and trees across the country, including in Austin. It is essentially when leaf tissue dies around the edges and can have several different causes.
What Causes It?
Because there are several potential reasons that leaf scorch can occur, an arborist will have to tell you the exact reason. It can happen when the soil doesn’t have enough moisture or if the leaves lose water too quickly and can’t replace it adequately. It is also possible that the roots of the tree were killed by compaction, excavation, or plant pathogens, meaning the leaves can’t receive enough water. The lack of water that results in bacterial leaf scorch can also be caused by bacteria or fungi invading the tree and then plugging the xylem, the vessels responsible for carrying water. Essentially, leaf scorch happens when the leaves of a plant don’t get enough water, but the reason for this lack of water can vary. The last of these is bacterial leaf scorch since it is transmitted by bacteria.
Common Bacteria That Cause BLS
Among the various bacteria that can clog the xylem of a tree and lead to bacterial leaf scorch, Xylella fastidiosa is among the most common. This particular bacterium has been linked to leaf scorch an incredible range of plants, including sweetgum, red maple, sycamore, elm, oak, and mulberry trees. It can also cause a different issue, Pierce’s disease, on grapevines or other problems like ragweed stunt, almond leaf scorch, periwinkle wilt, plum leaf scald, phony peach disease, and alfalfa dwarf.
How Bacterial Leaf Scorch Spreads
In the case of bacterial leaf scorch due to bacteria like Xylella, it will spread as this bacterium moves between plants. It can be carried by spittlebugs, leafhoppers, and treehoppers of all ages. The bacteria will either transmit immediately or wait about two hours to do so. The insect keeps carrying the bacteria, meaning it can spread it to multiple plants.
Recognizing BLS On Red Maples
When it affects red maple trees, bacterial leaf scorch will typically affect individual branches, with the number of them affected increasing every year. The leaves will look normal during the early portion of the season before leaf discoloration starts along the edges. By mid or late July, the discoloration will have reached the base and midrib of the leaf. In many cases, you will notice a border of dark reddish brown around the light brown area of dead tissue. A yellow halo separates this dead tissue from the healthy green tissue.
It is likely that red maples with BLS will experience premature defoliation starting in late August. Trees with this condition are also at a higher risk of damage due to stress.
Recognizing BLS On Elm Trees
Like red maple trees, the leaves on elm trees affected by bacterial leaf scorch will have a yellow border that keeps the green tissue and dead tissue separated. The scorching on these trees tends to start at the base of the tree before moving upward. Elm trees with BLS have a higher risk of elm bark beetles and Dutch elm disease.
Recognizing BLS On Oak Trees
Most of the time, red and pin oaks will develop bacterial leaf scorch and the other varieties of oak won’t, but white oak can also be affected. You once again get the distinctive yellow separation on the leaves and the scorch spreads closer to the leaf’s base with an undulating pattern over time. Red oaks are unlikely to suffer from defoliation due to bacterial leaf scorch, but red oaks may develop water sprouts.
Other General Symptoms
Most trees with bacterial leaf scorch will have the same pattern on their leaves, with the margins turning brown first. The disease tends to affect the oldest leaves first and the yellow border nearly always separates healthy and dead leaf tissue. In some cases, browned leaves will fall out. The symptoms of bacterial leaf scorch get worse over the course of three or eight years and by the end of this time, the entire tree will begin browning prematurely.
Confirming It Is BLS
Only an expert will be able to confirm that the leaf scorch affecting your tree is of a bacterial nature and whether it is caused by Xylella or another bacterium. They will need to conduct laboratory tests or send a sample to a third-party lab for testing. During the testing, experts can recognize Xylella by its lack of flagella and spore, thick rippled cell wall, and lack of growth on the conventional media used for bacteriology.
An untrained eye can confuse bacterial leaf scorch with Dutch elm disease or oak wilt. An important difference, however, is that BLS will repeat itself and worsen over time while the other diseases can kill a tree in months. You also won’t notice any sapwood streaking with BLS. Finally, bacterial leaf scorch causes browning to start at the edges of the leaves before moving inward while the other diseases brown the leaves more uniformly. Those unfamiliar with bacterial leaf scorch may also confuse it with heat stress, drought, or other causes of leaf scorch.
Controlling Bacterial Leaf Scorch
Your arborist or other tree expert will be able to work with you to create a plan to eliminate bacterial leaf scorch. Luckily, the bacteria typically require several years to kill a tree completely, giving you plenty of opportunity to take care of it. That being said, it can be complicated to treat bacterial leaf scorch because even if you get rid of the infected trees, the bacteria may have spread to the others nearby.
At the moment, the most effective treatment is an antibiotic known as tetracycline. Arborists inject this into the infected tree and the symptoms will temporarily go away completely or at least be reduced for about a year. The symptoms eventually reappear though. You can also limit the spread of the bacteria and resulting leaf scorch by removing dead branches and disinfecting your pruning tools between every cut.