Oak Wilt: Identification & Management … …. Mark Duff Certified Forester, Board Certified Master Arborist 1
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?
9 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 Oaks and other members of the Beech family (Fagaceae)
Above ground (long distance) via sap-feeding beetles: RED 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
11 How Is Oak Wilt Spread? Underground (localized) via interconnected root systems: LIVE 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 ~ % survival rate Live Oaks 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) Red Oaks Diagnosis in Individual Red Oaks
Live Oaks Foliar Symptoms in Live Oaks Veinal chlorosis / necrosis Tip burn / Marginal necrosis
Red Oaks Foliar Symptoms in Red Oaks Bronzing or water soaking
Fungal mats contain spores REDForm 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 Management Early detection and prompt action are essential for successful management of oak wilt. There are four primary approaches used to manage oak wilt: not cure These measures will not cure oak wilt but can significantly reduce tree losses. Prevention Trenching Fungicide Injection Planting
Prevention - Pruning February through June Peak beetle activity and fungal mat production occur in the spring; therefore, avoid wounding oaks from February through June. immediately paint 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 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 minimum of 100 feet at least 4 feet all root connections 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
Trenching Soil 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 notInjection does not stop root transmission of the fungus!
Fungicide Injection Success depends upon the health of the tree, application rate, and injection technique.
Fungicide Injection scientifically proven Several 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
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
Recommended Trees American smoketree Arizona walnut baldcypress bigtooth maple bur oak Carolina buckthorn cedar elm chinkapin oak desert willow escarpment cherry Lacey oak littleleaf leadtree mescalbean Mexican plum pecan possumhaw TX or MX redbud rusty blackhaw Texas crabapple Texas sophora
“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 Shares Cost-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 $ per individual per year with a maximum of $10, 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 NOT 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 Information Partnership website: HOW TO Identify and Manage Oak Wilt in Texas brochure