Butternut Canker

Sirococcus clavigignenti-juglandacearum

Invader Images

    • Butternut canker
    • Butternut canker
    • Butternut canker
    • Stained wood and scarring of outer bark
    • Outer bark becomes loose, revealing oval shapes of stained wood
    • Cankers often ooze sap from beneath the bark
    • Stained wood beneath bark

Identification

Butternut canker is caused by a fungus (Sirococcus clavigignenti-juglandacearum) that infects butternut (Juglans cinerea) through openings such as buds, leaf scars, and insect wounds. Spores of the fungus enter the tree and create cankers that are elongated, sunken, often with an inky black center and whitish margin. When large cankers form (or many smaller cankers coalesce), twigs and branches become girdled, resulting in dieback. Trunk and buttress roots can also become girdled, ultimately killing the tree. The spores can be carried on the nuts and infect the tree upon germination. The fungus is spread by rain-splashed spores, wind, and insects. Spores can remain viable on dead trees for at least two years. Armillaria root rot is often associated with trees infected with butternut canker and may hasten mortality.

Signs and symptoms

• Dead or dying branches at the tops of butternut trees
• Cankers in the bark will ooze black fluid in the spring and have a dark center and whitish margin in the summer.
• Young cankers often appear around leaf scars, buds, or wounds and may be elongated and sunken into the bark.
• Old cankers may have layers of overgrown trunk tissue and loose bark covering them.
• Stained wood beneath the bark that is dark brown to black and oval shaped.

See image slideshow above for signs and symptoms.

Biology

Origin

Butternut canker was first discovered in the United States in Wisconsin in 1967. It is thought to have been introduced from abroad, although its native range and means of arrival in the US is unknown. Since its arrival 90% of the butternuts in the US have become infected throughout the tree’s native range.

Life Cycle

The disease is caused by a fungus that grows under the bark and produces thick, black hyphal pegs (or stomatal columns) that cause the bark to blister and split open. Asexual fruiting bodies, called pycnidia, are produced and released in gelatinous tendrils or creamy masses. Fruiting bodies are more likely to develop on dead branches than on cankered areas of the stem. Spores are moved by rain, wind, insects, birds, and rodents throughout the growing season.

threat

In late stages of the disease, multiple cankers will form on the branches, stem, and roots. The infected tree will stop producing nuts. The cankers grow and join together, killing the affected branches. If the cankers girdle the stem, the tree will die. Cankers also serve as entry points for other pathogenic and decay organisms. 

Management Options

  • Butternut is a species at risk. To conserve butternut in the landscape, retain potentially resistant trees (trees free of cankers and with more than 50% of crown alive) and trees that appear to be disease-tolerant (those with less than 20% of stem/root flare circumference affected by cankers and more than 70% of crown alive).
  • Efforts are underway to locate and propagate potentially resistant trees. Contact the VT FPR Forest Biology Lab if you find a healthy butternut with no symptoms of butternut canker, especially if it is growing among diseased trees. 

Vermont Distribution

Butternut canker has spread throughout Vermont.

North America distribution map.

Citations

Photo Credit

Joseph OBrien, USDA Forest Service, Bugwood.org

Mike Ostry, United States Department of Agriculture, Forest Service, Bugwood.org

Tom Creswell, Purdue University, Bugwood.org

USDA Forest Service, Northeastern Area, USDA Forest Service, Bugwood.org

Manfed Mielke, USDA Forest Service, Bugwood.org

information credit

Natural Resources Canada

New York Times: Protecting a Little-Known Tree From an Insidious Disease

Northern Woodlands: Saving the Butternut Tree

University of Vermont Forest Pathology: Butternut Canker Disease

US Forest Service: How to Identify Butternut Canker and Manage Butternut Trees