Oak Wilt North

Ceratocystis fagacearum

Oak wilt is a vascular wilt disease caused by the fungus Ceratocystis fagacearum. This fungus grows in the water conducting vessels of the tree, which kills the tree.

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Treatment Strategy

The treatment strategy differs significantly between Red Oaks and the White oak family (white and bur oaks).

Oak Wilt Treatment - Red Oaks

Red Oak treatment strategy involves the combination of breaking root grafts and preventative Alamo® treatments. Red oaks that are showing any symptoms of infection cannot be saved, but trees that are root grafted to infected trees can be protected. Since Alamo® only saves the tree being treated and does not prevent root graft infections to adjacent trees, breaking of root grafts is critical to stopping the disease progression. See the diagram to help determine which trees to treat and where the trench should be placed. Alamo® treatments are usually done twice, 2 years apart.

Oak Wilt Treatement for Bur and White Oaks

Bur and White oaks can be cured of oak wilt disease with a treatment of Alamo® about 99% of the time. Typically, the best method is to treat the infected bur or white oak as well as the root grafted non-infected trees that are close by. In some cases, root graft disruption is needed, but typically is not used. Retreatment is only repeated if oak wilt symptoms reappear.

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Oak Wilt North Treatment Option 1

Alamo® Application 

Alamo® treatment involves injecting the fungicide directly into the root flares of your oak using the Low Volume Macro-Infusion Pump equipment. Alamo® protects trees from root graft infections and lasts for two years, so two cycles of injections are recommended to get a current infection under control.

Treatments are only successful if applied preventatively on healthy red oaks, or on white or bur oaks showing less than 30% symptoms. For complete instructions see the Low Volume Macro-Infusion Application Guide or view the application video.

Find out more about quick tips on oak wilt treatments.

Application Type Low Volume Macro-Infusion

DIY Product/Equipment Needed:

Alamo®

Low Volume Macro-Infusion Kit

• Shovel and hand trowel

• Gloves

• Stiff bristled hand brush

Oak Wilt North Treatment Option 2

Root Graft Disruption For Red Oaks

Root graft disruption is an important means of controlling oak wilt in red oaks. The most commonly used equipment for breaking root grafts is a trenching machine, or a vibratory plow. If the oaks are located in a sand plane, the roots can be as deep as 5 feet and a vibratory plow must be used.

Root graft disruption is a service that is often done by a professional. If you do choose to take this on yourself, be sure to call the utility company to mark your utility lines so you can avoid cutting them and the possibility of injuring yourself.

Application Type -Root Grafting

Equipment Needed:

• Contact your city forester

Oak Wilt North Treatment Option 3

Removal of Diseased Red Oaks

Red oaks with oak wilt symptoms should be removed only after all adjacent non symptomatic red oaks have been treated with Alamo and after root-graft barriers have been established. Wilted oaks in the red oak family can produce fungal spore mats between the bark and the wood. The purpose of removing trees is to protect against spore mat production, which does not take place until the following April and May.

Application Type -Tree Removal

Equipment Needed:

• Contact a certified arborist for information about tree removal

Oak Wilt North DIY Kit

Option 1

Application Type – Low Volume Macro-Infusion

DIY Product/Equipment Needed:

Alamo®

Low Volume Macro-Infusion Kit

• Shovel and hand trowel

• Gloves

• Stiff bristled hand brush

Option 2 

Application Type -Root Grafting

Equipment Needed:

• Contact your City Forester

Option 3

Application Type -Tree Removal

Equipment Needed:

• Contact a certified arborist for information about tree removal

How Is It Spread?

There are two ways oak wilt spreads:

1. Overland transmissions spread by a sap-feeding insect called Nitidulidae (aka “the Picnic Beetle”). These insects feed near oak wilt spore mats that grow on red oaks that died the season before. They then feed on sap that flows from a fresh tree wound. This type of infection requires an existing wound on a tree so oaks should only be pruned during the dormant season when the spore mats are not active. Since red oaks grow in groups, a new overland infection starts what is called an infection center.

2. Underground infections called root graft transmissions. Root graft transmissions are responsible for most oak wilt infections. Trees of the same species growing close to each other are usually attached by their root systems. Once a single tree becomes infected by a Nitidulid, the fungus grows down to the root system and spreads to neighboring oak trees via root grafts. Root grafts form between trees of the same species. Their roots fuse together to enhance water and nutrient uptake.

Susceptible Trees

Red oaks, Pin oaks, White oaks and Bur oaks can all be infected with the fungus that causes oak wilt.

Symptoms

Red, White and Bur oaks exhibit different symptoms of oak wilt disease.

Oak Wilt Symptoms in Red Oaks

Of the three groups of oaks, red oaks are the most susceptible and typically die within 4-6 weeks of the first visible symptoms.

• Leaves wilt and turn brown. This starts at the top of the tree and quickly progresses downward.

• The leaves will fall off the tree and be half green and half brown in color. Typically all other oak issues the leaves will stay attached to the tree and be a light brown.

• Only in very late season infections do leaves remain on the tree, and these may turn a flat orange color.

• Visible staining is present in the wood underneath the bark of effected branches

• Infected Red oaks produce spore mats the following spring.

Oak Wilt Symptoms in Bur Oaks

Bur Oaks are moderately resistant to the oak wilt fungus. They typically die over a 1-3 year period.

Wilting will start in one branch and move to other branches in a progressive manner.

• The leaves will fall off the tree and be half green and half brown in color. With all other oak issues, the leaves typically stay attached to the tree and are a light brown.

• Sometimes the leaves will take on a twisted dull olive -colored look.

• Wood staining is often present, but is sometimes difficult to see.

Oak Wilt Symptoms in White Oaks

White oaks are the most resistant to the oak wilt fungus and it can take as long as 3 -10 years for oak wilt disease to kill a white oak.

Wilting often occurs on single branches. Branches die slowly, and the disease sometimes stops for indefinite periods of time before starting to grow again.

• The leaves fall half green, half brown, but they can also take on a dull olive color as they begin to wilt.

• Wood staining is sometimes present, but it is not a reliable indicator.

Lookalikes

Problems sometimes mistaken for oak wilt:

Anthracnose: Anthracnose-effected leaves curl at the location of the brown tissue, whereas oak wilt effected leaves remain flat.

Two-lined chestnut borer: The leaves of TLCB trees rarely fall before they have completely turned brown, nor do they fall in the numbers associated with oak wilt.

Spider mite: Spider mites attack small, random pockets in the tree, unlike the more top-down oak wilt symptoms

Herbicide damage: Herbicide damage often causes the leaves to curl and grow in abnormal patterns, especially on newly formed leaves and shoots.

There are several disorders of oak that can be mis-identified as oak wilt. Very few cause leaf drop as oak wilt does.

Related/Similar Problems

Two-lined Chestnut Borer (TLCB), Chlorosis

Timing

Spring through summer

Urgency

High

Risk of Spreading

High

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