Hypoxylon Fact Sheet 1

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Understanding, Recognizing and Keeping Hypoxylon Canker of Oaks at Bay

Part 1. Cause and BiologyHypoxylon canker is a tree disease appearing as a necrotic (dead) lesion on limbs, branches and trunks  of affected trees. The canker develops just under the  bark (Figure 1), but in advanced stages causes a white rot type of decay of the sapwood. For this reason, Hypoxylon canker not only contributes to tree mortality, but compromises the structural integrity of a tree making it a danger to life and property.

Hypoxylon beneath bark of disease tree.

Fig 1 Hypoxylon beneath bark of disease tree.

The disease is caused by a fungus named Biscogniauxia (Hypoxylon) atropunctatum. This fungus is an opportunistic pathogen, meaning it does not affect healthy and vigorous trees. However, Hypoxylon can quickly colonize weakened or stressed trees. It has been diagnosed on trees growing in many different habitats, such as forest sites, pastures, parks, green spaces and urban development areas. Hypoxylon canker can affect any type of oak, including; black, blackjack, laurel, live, post, southern red, Texas red, water and white oaks.
Since Hypoxylon is a fungus, it spreads from diseased to healthy trees by spores. Opportunistic fungi, however, are usually already present on many trees, causing disease when tree resistance is insufficient to prevent them from infecting. There are many sources of stress capable of decreasing the resistance of trees to  opportunistic pathogens.

Stress FactorsUrban development Many factors in urban environments stress trees. Construction damage, for example, wounds roots and causes site disruption that result in tree stress and decline. Constructing swimming pools, sidewalks, patios, and driveways can damage essential roots and root flares that provide necessary water and minerals for a healthy tree. Soil compaction and addition of fill soil cause

Fig 2. Typical site disruptions during home construction.

Fig 2. Typical site disruptions during home construction.

drainage issues and suffocate roots. All these factors set in motion a chain of events leading to stress, decline and tree death (Figure 2). During  decline,
Hypoxylon attacks the  trees and contributes to their mortality.
Natural factors Climatic conditions such as heat, drought, ice storms, hail damage, lightning, and flooding are capable of predisposing trees to infection by Hypoxylon. Insect attacks and other diseases, such as oak wilt and root rots, induce stress and cause a tree to be susceptible to infection by Hypoxylon.
Symptoms and Signs and Control of Hypoxylon canker are covered in Parts 2 and 3 of these fact sheets.

Prepared by Sheila McBride1 and Dr. David Appel2
Diagnostician, Texas Plant Disease Diagnostic Laboratory1 and Professor of Plant Pathology and Microbiology2
Texas AgriLife Extension Service; The Texas A&M University System
May 22, 2009


The information given herein is for educational purposes only. References to commercial products or trade names are made with the understanding that no discrimination is intended and no endorsement by Texas AgriLife Extension Service personnel is implied.
Educational programs of the Texas AgriLife Extension Service are open to all people without regard to race, color, sex, disability, religion, age, or national origin.
The Texas A&M University System, U.S. Department of Agriculture, and the County Commissioners Courts of Texas Cooperating

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