Got Nature? Blog

Recently, questions and concerns have come to the Division of Forestry from forest landowners and Consultant Foresters regarding the sale of black walnut trees now, because of Thousand Cankers Disease (TCD).

First, an update on the status of TCD in Indiana.

The Divisions of Entomology & Plant Pathology and Forestry have conducted TCD surveys since 2011 following the first confirmed detection of TCD in the eastern United States – Knoxville, TN August 2010.

The annual surveys include two visual surveys for symptomatic trees and a trapping survey for the Walnut Twig Beetle (WTB), the confirmed vector of the TCD fungus, Geosmithia morbida.

One visual survey occurs in 10 urban areas/cities each year. The other visual survey is gypsy moth trap tenders reporting walnut trees (healthy or with dieback) near each trap location.

In 2015, the urban areas/cities survey examined 1,431 walnut trees and the trap tenders reported 842 walnut trees. Of these only 26 had dieback and none were confirmed with TCD. Since 2011 over 40 urban areas/cities totaling over 3,700 walnut trees and over 5,200 walnut trees reported by trap tenders have been surveyed and less than 2% reported dieback and none had TCD.

The WTB survey involves setting traps baited with the WTB lure. A detection survey sets traps at high risk sites (sawmills, veneer mills, log consolidation yards, green waste sites and along the Ohio border to Butler County Ohio). A delimit survey is conducted at the sawmill in Franklin County and the walnut plantation at Yellowwood State Forest in Brown County due to the detection of WTB and Geosmithia morbida, respectively, at these locations.

In 2015, 249 traps were placed in the detection and delimit surveys. 2,592 samples were examined from the traps. The only detection of WTB was from traps at the sawmill in Franklin County.

Results of the survey efforts are:

• TCD has NOT been detected and confirmed from a black walnut tree in the state of Indiana.
• There are NO dead or dying black walnut trees in Indiana from TCD.
• There is NO widespread TCD mortality in Indiana and none is expected in the near future
• The components of TCD – WTB and Geosmithia morbida – have been detected in Indiana.
• WTB has been detected in traps, NOT in standing trees.
• Geosmithia morbida has been detected from a weevil, Stenomimus pallidus, which was collected from a study tree in the Yellowwood State Forest plantation.
• There are NO TCD infected walnut trees in the Yellowwood State Forest Plantation.

Also, there are NO reports of widespread walnut mortality from TCD in the infested states of Tennessee, Virginia, North Carolina, Maryland, Pennsylvania and Ohio.

Therefore, if you are approached to sell your black walnut trees now because the “Walnut Disease” (TCD) is coming and you should sell before it gets to your woods, the response and recommendation is to contact your consulting forester or district forester for advice, follow your current management plan and do not sell the walnut just because of TCD.

I do not anticipate rapid and widespread mortality of walnut once TCD is confirmed from an Indiana black walnut tree.

For more information, visit the Indiana Department of Natural Resources’ Thousand Canker Disease webpage or contact
Forest Health Specialist/State Entomologist Phil Marshall at 317.232.4189 or pmarshall@dnr.in.gov.

Resources:
Thousand Cankers Disease – Indiana Department of Natural Resources (IDNR).
Thousand Cankers Disease – website provided by Purdue FNR, HTIRC, American Walnut Manufacturers Association, and the Walnut Council.
Study: Fungus behind deadly disease in walnut trees mutates easily, complicating control – Purdue Agriculture News.

Phil Marshall, Forest Health Specialist and State Entomologist
Indiana Department of Natural Resources (IDNR)