Thousand Cankers Disease of Walnut

A formal exterior quarantine for thousand cankers disease of walnut (TCD) was signed into effect in August 2011 and repealed in August 2021. At one time, seventeen other states had exterior quarantines in place against TCD but those quarantines are now being repealed because TCD has not manifested as a significant disease concern in the eastern U.S.

What is Thousand Cankers Disease?

Mortality of black walnut trees was observed in western and southwestern United States since the 1990s. In 2008 in Colorado an insect (walnut twig beetle) and fungus (Geosmithia morbida) combination was identified as the cause of the mortality, which had come to be known as thousand cankers disease because of the numerous cankers on the stems and branches of the walnut trees.

In 2010, TCD was detected in Tennessee, which was the first time it had been discovered within the native range of eastern black walnut. At that time, many states, including Minnesota, were concerned that TCD may have the same impact in the eastern U.S. that had been seen in the western U.S. As a result, many eastern states, including Minnesota, enacted exterior quarantines to prevent the movement of materials that could carry TCD into their state.

Since 2010, the insect/fungus complex has been discovered in several other eastern states. However, TCD has not manifested as a significant disease in the eastern U.S. and it is now accepted that the root causes of this disease are more complicated than simply the presence of the fungus and the insect.

In consideration of these circumstances, the Minnesota Department of Agriculture has determined that it is no longer necessary to maintain regulations related to TCD.

brown colored beetle smaller than a grain of rice.

Walnut twig beetle, smaller than a grain of rice, carries thousand cankers disease fungus that affects walnut trees. Steven Valley, Oregon Dept. of Agriculture.

small dark spots on walnut branch caused by thousand cankers disease
Small cankers on walnut branch caused by thousand cankers disease. Whitney Cranshaw, Colorado State University.