“We have much to lose from the spread of TCD,” Marshall said. “It is important that we repeat the study to understand the role of the weevil and occurrence of the fungus in the trees.”
Walnut twig beetles that typically carry the fungus are smaller than a pinhead. They bore into walnut branches, feeding on the tree’s tissues and depositing the fungus that creates a canker, or dead area, under the bark. Multiple feedings cause the formation of thousands of cankers under the bark and destroys the tree’s ability to transport water and nutrients. Gradually, branches die, and then the entire tree eventually dies.
Walnut trees affected by the disease typically die within two to three years after symptoms are noticed.
Black walnut is the most valuable tree in Indiana based on the dollar value of wood produced, mainly as walnut veneer but including timber and nuts.
There are an estimated 31.5 million walnut trees in Indiana. Approximately 17.7 million board feet of black walnut is harvested annually with a value of $21.4 million. If all forest walnuts in Indiana were lost because of TCD, it would represent a $1.7 billion loss. State forester John Seifert, IDNR Division of Forestry director, said the estimates do not include the value of urban trees and investments landowners have made for black walnut plantations and tree improvement over the past 30 years.
This detection does not change or eliminate the current TCD quarantine that restricts movement of walnut into Indiana from other infested states. Indiana sawmills, veneer mills and log buyers must still comply with Indiana’s TCD quarantine before they bring walnut from infested states into their location.
Forest landowners do not need to harvest their black walnut trees as a result of this detection.
Persons who notice a suspicious decline in black walnut trees or otherwise suspect an infestation of TCD should call the IDNR at 866-663-9684. If approached by someone offering to remove black walnut trees because of the disease, notify the IDNR or a consulting forester to have the tree checked.
More information about TCD can be found at dnr.IN.gov/entomolo/6249.htm.