The fungus was discovered as a result of a survey for insect pests and fungi in Indiana and Missouri. The U.S. Forest Service-led survey was a cooperative effort with scientists at the University of Missouri and Purdue University. The survey did not detect the fungus, walnut twig beetle or the weevil in Missouri. Neither this survey nor any other previous surveys have detected the walnut twig beetle in Indiana.
Originally found in New Mexico, TCD affects many types of walnut trees to varying degrees but is lethal to black walnuts, which often are grown in plantations in Indiana but are also common in the state’s urban and rural forests. Indiana joins Maryland, North Carolina, Ohio, Pennsylvania Tennessee, Virginia and eight western states with the disease.
The quarantine only restricts movement of black walnut out of the plantation. Movement of black walnut from other areas of Brown County is not restricted. The trees in the plantation do not currently show symptoms of the disease, according to Marshall. Should the disease status in the plantation change, the trees can be cut and destroyed to prevent spread out of the plantation.
“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. DNR officials say 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, director of the DNR Division of Forestry, 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.
The Indiana DNR says forest landowners do not need to harvest their black walnut trees as a result of this detection. If you notice a suspicious decline in black walnut trees or otherwise suspect an infestation of TCD, call the DNR toll-free at 1-866-663-9684. If approached by someone offering to remove black walnut trees because of the disease, notify the DNR or a consulting forester to have the tree checked.
More information on TCD is at dnr.IN.gov/entomolo/6249.htm