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Oak Wilt: Identification & Management

Hill Country Master Naturalists

23 September 2015

Robert EdmonsonBiologist III, ISA Certified Arborist

The Impact of Oak Wilt• “Oak wilt is one of the most destructive tree diseases” (Young, 1949).

• “…. this disease has the potential of becoming one of the worst diseases to attack the forests of the state.” ( True and Gillespie, 1961).

• “Ceratocystis fagacearum, the cause of oak wilt, is a fungus with the potential to be one of the most destructive of all tree pathogens.” (Gibbs and French, 1980).

• “Oak wilt is now one of the most serious forest diseases in the country” ( Johns and Phelps, 1992).

The Impact of Oak Wilt

Thousands of acres throughout central and west Texas have been adversely

affected by oak wilt.

The Impact of Oak Wilt

Oak wilt may reduce urban and suburban property values by 15-20%.

What Is Oak Wilt?

• Caused by the fungus Ceratocystis fagacearum

• Primary vascular pathogen

• Relies on insects for transportation

• Produces fungal mats

• Heat sensitive

• Unknown origin

Where is Oak Wilt?

Where is Oak Wilt?

Where is Oak Wilt?

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What Trees Are Susceptible?

Red Oaks are extremely susceptible to the pathogen and play a unique role in disease spread.

White Oaks are more tolerant of the disease; however, they are NOT IMMUNE to infection!

Live Oaks are intermediate in susceptibility; however, they are seriously affected due to their vast, interconnected root systems

that allow for disease spread among trees.

All Oaksand other members of the Beech family

(Fagaceae)

Above ground (long distance) via sap-feeding beetles:

Fungal spores are picked up from certain infected RED oaks and carried to fresh wounds on other oak species. New infection

centers are started in this manner.

How Is Oak Wilt Spread?

Sap Beetle

Fungal Mat Fresh Wound on

Oak

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How Is Oak Wilt Spread?Underground (localized) via interconnected root systems:

This occurs primarily in LIVE oaks and is responsible for the majority of spread and tree deaths in central Texas.

Root Grafts

Rate of spread averages 50 feet to 75 feet per year.

Live Oak Mott

How Is Oak Wilt Spread?

Red Oak Center

Live Oak Center

Diagnosis in a Population of Trees

• Rapid defoliation• Death in 3 to 6 months• Spread to adjacent trees• No fungal mat formation• ~ 5 - 15% survival rate

Diagnosis in Individual Live Oaks

• Maintain leaves, then defoliate• Death in 4 to 6 weeks• Possible spread to adjacent trees• Possible formation of fungal mats• 100% mortality (no survivors)

Diagnosis in Individual Red Oaks

Foliar Symptoms in Live Oaks

Veinal chlorosis / necrosis

Tip burn / Marginal necrosis

Foliar Symptoms in Red Oaks

Bronzing or water soaking

• Fungal mats contain spores

• Form only on RED oaks

• Form under bark

• Can have multiple mats per tree

• Produce a sweet odor like rotting fruit

• Mat production accelerated by cool, moist weather (springtime in Texas)

• Trees infected in fall / winter produce mats

Presence of Fungal Mats

Taking Samples

• Bole (preferred) or branch samples

• Confirms presence of pathogen

Oak Wilt ManagementEarly detection and prompt action are essential for successful

management of oak wilt.

There are four primary approaches used to manage oak wilt:

These measures will not cure oak wilt but can significantly reduce tree losses.

Prevention

Trenching

Fungicide InjectionPlanting

Prevention - Pruning

Peak beetle activity and fungal mat production occur

in the spring; therefore, avoid wounding oaks from February through June.

Regardless of season, immediately paint all pruning cuts and other wounds to oaks. This discourages contaminated sap-feeding beetles from visiting these wounds and introducing

oak wilt into these trees.

Prevention - Red Oak Management

Destroy infected red oaks to prevent fungal mat formation.

Never use infected red oaks for firewood!

Prevention - Firewood

• Transport and use only dry, well-seasoned firewood

• Leave unseasoned wood on site one year before moving

• Do not store infected wood near healthy trees

• Cover wood with clear plastic and bury the edges to prevent insects from leaving the pile

Trenching

Trenches must be placed a minimum of 100 feet ahead of the disease, excavated to at least 4 feet (sometimes deeper), and

sever all root connections to be effective.

100’

100’ minimum

Diseased

Healthy

TrenchingSoil depth and texture will

determine equipment choice.

Pushing / Rouging

Removing all oaks within the boundaries of the trench, specifically

the healthy and pre-symptomatic trees, can improve barrier effectiveness.

Fungicide Injection

• Used to protect high-value oaks in advance of an expanding oak wilt center

• Best candidates are healthy or pre-symptomatic live oaks 50 feet to 150 feet from symptomatic trees

• Injection does not stop root transmission of the fungus!

Fungicide Injection

Success depends upon the health of the tree, application rate, and injection technique.

Fungicide InjectionSeveral products are currently labeled and registered for this

treatment; however, only macro-injections of Alamo® have been

scientifically proven effective and continue to be the industry standard.

• Bark is thinner below the soil line

• Increases the number of potential injection sites

• Spreads out the wounding, especially if future injections are needed

• Research has demonstrated superior distribution of fungicide in the tree

Macro-Injection Advantages

“Alternative” Products and Methods

Tebuject

Criteria for Successful Injections

• Reliable• Verifiable documentation of research results• Must increase survival of treated trees over natural

population• Safe• Economical• Reasonably easy to apply• Legal

• Native or adapted to the local environmental conditions

• Tolerant of temperature extremes, amount and pattern of precipitation, and local soil conditions

• Not invasive nor detrimental to the local environment

• Preferably multi-functional in the landscape

Tree Planting

Tree Planting

• Avoid planting monocultures

• Create diversity in the landscape

• Avoid wounding oaks during planting

Tree Planting

• Site• Season• Hole• Drainage• Pruning(?)• Foreign Materials• Depth• Backfill• Staking(?)• Mulch• Protection• Maintenance

Tree Planting

Recommended TreesAmerican smoketree

Arizona walnut

bald cypress

bigtooth maple

bur oak

Carolina buckthorn

cedar elm

chinquapin oak

desert willow

escarpment cherry

Lacey oak

littleleaf leadtree

mescal bean

Mexican plum

pecan

possumhaw

TX or MX redbud

rusty blackhaw

Texas crabapple

Eve’s necklacepod

“The overall goal of the Texas A&M Forest Service’s Cooperative Oak Wilt Suppression Project is to minimize the spread of oak wilt

(Ceratocystis fagacearum) in central Texas.”

• Provide public awareness and education about the disease• Identify and map mortality centers with ground verification of

oak wilt• Provide treatment recommendations and cost-shares (when

applicable) to private landowners• Conduct post-suppression evaluations on cost-shared

treatments• Establish and maintain detailed and accurate records

Oak Wilt Suppression Project

Cost SharesCost-shares, disbursed through the Oak Wilt Suppression Project,

may be available to private landowners for the following efforts:

• Containment trenching around oak wilt centers

• Pushing or rouging of all oaks within the boundaries of cost-shared trenches

• Removal of diseased red oaks in urban areas

Cost-shares shall consist of 40% of actual costs not to exceed $2000.00 per individual per year with a maximum of $10,000.00

per project per year.

Cost Shares

• Complete containment of the disease center (natural land features and existing underground infrastructure can be used in select cases)

• Relative isolation of the disease center from other disease centers

• High potential for fungal mat formation (red oaks)

• Compliance with Cultural Resources Preservation Act

The following criteria are required to qualify for cost-shares:

Cost Shares

• Removal of dead trees

• Trenching around healthy stands of trees

• Secondary trenches

• Engineering charges, consulting fees, or permit fees

• Loss or reduction in revenues from the land

• Stump grinding

• Fungicide treatments (injection)

• Replanting or landscaping

Items NOT eligible for cost-shares include:

Cost Shares

• Cost-share Application

• Treatment Plan

• Cultural Resources Survey Form

• TARL Records Check

• Treatment Maps

• General Location Map

• Underground Utility Waiver

• Cultural Resources Acknowledgement Form

• W-9 Tax Identification Form

There is an application process:

Texas A&M Forest Service Central Texas

Regions

Oak Wilt Resources

Oak Wilt Resources

Oak Wilt Information Partnership website:

http://texasoakwilt.orgHOW TO Identify and Manage Oak Wilt in

Texas brochure

Other Informational Websites

tfsweb.tamu.edu

texastreeplanting.tamu.edu

tfsfrd.tamu.edu/MapMyProperty/

texasinvasives.org

treesaregood.org

texasconservation.org

Questions?

Thank You!Robert Edmonson

Biologist III / ISA Certified ArboristTexas A&M Forest Service