Bacterial Leaf Scorch

Xylella fastidiosa

Bacterial Leaf Scorch (BLS) is a devastating disease of shade trees that is caused by the xylem-inhabiting bacteria Xylella fastidiosa. Leaf desiccation is the most prominent visible symptom, although infected trees may eventually display dieback, branch death, and die prematurely. Commonly infected trees include oaks, elms, sycamores, sweet gum as well as other varieties.

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Treatment Strategy

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.

Research by Kostka, Tattar, and Sherald has shown that bacterial leaf scorch can be successfully managed with an annual application of an oxytetracycline antibiotic. This treatment is effective at suppressing bacterial growth in the water-conducting vessels of the tree - where most of the injury occurs.  Other practices that help the tree include: watering during dry periods, mulching the root zone, and applying a growth regulator, such as Cambistat®, which can increase the drought tolerance and reduce water loss.  Cambistat® increases root growth, defense chemicals, and chlorophyll in the leaves by about 35%.

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Bacterial Leaf Scorch Treatment Option 1

Mulching the Tree (Optional)

Applying a 3″ deep ring of mulch at the base of the tree will reduce grass competition, increase moisture retention, and increase the fibrous root system of the tree. The larger the area the better; however, even a ring that extends 5 feet from the trunk can have tremendous benefit.

Application Method – Cultural Practices

DIY Equipment Needed:

• Rake and shovel

• Mulch

Bacterial Leaf Scorch Treatment Option 2

Treating With Cambistat® (Optional)

Cambistat® must be carefully applied in EXACTLY the right amounts as shown in the application guide.  Dosing is determined by tree species as well as tree size.  Cambistat® is applied to the soil in a small trench at the base of the tree, and can be applied at any time.  Typically, it takes at least one year for darker, greener leaves and reduced bacteria growth to become apparent, but these benefits last for three years.

Application Type Soil Drench or Soil Injection

DIY Product/Equipment Needed:

• Cambistat®

• Graduated cylinder measuring in mL

Soil Drench: Bucket or watering can; shovel or trowel; soil drench kit

Soil Injection: HTI Soil Injection Kit

Bacterial Leaf Scorch DIY Kit

For Bacterial Leaf Scorch Treatment Option 1

Application Method – Cultural Practices

DIY Equipment Needed:

• Rake and shovel

• Mulch


For Bacterial Leaf Scorch Treatment Option 2

Application Type – Soil Drench or Soil Injection

DIY Product/Equipment Needed:

• Cambistat®

• Graduated cylinder measuring in mL

• Soil Drench: Bucket or watering can; Shovel or trowel; Soil Drench Kit

• Soil Injection: HTI Soil Injection Kit

How Is It Spread?

Bacterial leaf scorch is spread via xylem-feeding insect vectors, including sharpshooters, treehoppers, leafhoppers, and spittlebugs. It may also spread from one tree to another by root grafts.

Susceptible Trees

Oaks: red oak, pin oak, bur oak, white oak, willow oak, (Approximately 12 other species of oak), Sycamore, American elm, Maples: red maple, sugar maple, mulberry, sweet gum, and almond.

Symptoms

When bacteria colonize the xylem vessels, the availability of water to the leaves is restricted and scorch develops. Symptom severity tends to increase when drought stress is also present.

• Leaves develop normally early in the season and symptom expression begins in June and July.

Necrosis begins along the leaf margin and spreads toward the veins and petiole in an irregular pattern.

• Green tissue is separated from necrotic tissue by a band or halo of yellow or reddish brown bands.

• Bacterial leaf scorch symptoms will reappear in the same limbs from one year to another and eventually spread to other limbs.

• Infected trees display an overall decline in vigor, branch dieback, and premature death.

Lookalikes

Oak wilt

Related/Similar Problems

Drought stress, stem girdling roots, insect infestations.

Timing

Spring; before July

Urgency

High

Risk of Spreading

Moderate

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