The Purdue Plant and Pest Diagnostic Laboratory

Hot News from the P&PDL
August 31, 2010

Thousand Cankers Disease

Janna Beckerman, Gail Ruhl and Tom Creswell, Department of Botany & Plant Pathology, Purdue University

Thousand cankers (TCD) is a newly recognized disease of certain species of walnuts (Juglans spp.). The disease results from the combined activity of the walnut twig beetle (Pityophthorus juglandis) and a canker producing fungus in the genus Geosmithia (proposed name Geosmithia morbida). Originally, the disease was thought to be restricted to the western United States where over the past decade it has been involved in several large scale die-offs of walnut, particularly black walnut, Juglans nigra. Unfortunately, it was recently diagnosed in Knoxville, TN, and there is tremendous concern that it may have been transported to other areas east of the Mississippi, including Indiana.The Indiana Department of Natural Resources has issued an emergency rule banning the transportation of walnut products from nine western states and Tennessee to prevent the introduction of Thousand Cankers Disease (TCD) that afflicts black walnut trees and other walnut species, including butternut.

This disease was first recognized and described in 2008 by Ned Tisserat and Whitney Cranshaw of the Department of Bioagricultural Sciences and Pest Management, Colorado State University.

TCD is a significant threat to Indiana black walnuts. However, it is important to note that other problems may resemble thousand cankers, including many common abiotic disorders. These include freeze damage, and drought (although in both Colorado and Tennessee, initial diagnosis of drought was wrong). Other disease look-alikes include Fusarium canker, Phytophthora canker and Anthracnose.

What to look for:
Look for trees with existing crown dieback and individual branches that show flagging - either of yellowing leaves remaining attached or leaves that have collapsed and wilted. The latter is a somewhat stronger possible symptom. Try to collect a dead or dying limb and look for the minute exit holes. (When peeled carefully the exit holes will have associated larval galleries.) This can be considered confirmation as walnut twig beetle = Geosmithia morbida = thousand cankers disease. Remember that, despite the name of the beetle, this insect does not colonize walnut twigs, despite being a "twig beetle" of the genus Pityophthorus. Thus, branches of 1-2 inch diameter are most likely to have evidence of colonization. The cumulative effect of numerous cankers produces limb girdling that causes the yellowing, flagging and branch dieback.

Sample Submission:
It is important to verify the Thousand Cankers disease, particularly in locations where the walnut twig beetle and Geosmithia have not previously been reported. Walnut branch samples from trees suspected of having Thousand Cankers may be sent to the Purdue Plant and Pest Diagnostic Lab for verification. Select branches that are still alive but have evidence of beetle galleries and cankers and put 4-5 inch sections of the branch in a Ziploc bag without water or wet paper towels. Place this bag in a second Ziploc bag, seal tightly and mail to the address provided below. Phoning ahead to the Plant and Pest Diagnostic Lab (765-494-7071) of sample shipments is strongly encouraged.

Plant and Pest Diagnostic Laboratory
LSPS-Room 101, Purdue University
915 W. State Street
West Lafayette, Indiana 47907-2054

 

Tisserat, N., W. Cranshaw, D. Leatherman, C. Utley, and K. Alexander. 2009. Black walnut mortality caused by the walnut twig beetle and thousand cankers disease. Plant Health Progress. August 11, 2009. 10 pp. (This is the original description of the disease in a peer reviewed journal)

 

More links and quarantine info on Thousand Cankers Disease

Click image to enlarge

Walnut tree

Walnut tree

Walnut twig beetle

Walnut Twig Beetle
(Pityophthorus juglandis) is tiny,
1.5-1.9mm long

Bark

Cankers are hidden under the bark, often evidenced only by a tiny hole make by the beetle, or surface stains

Spores

Spore making structures

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service