Thousand Canker Disease

by Aahan Kotian

The Culprit

Thousand Canker Disease is caused by a beetle known as the Walnut Twig Beetle or Pityophthorus Juglandis which harbors a fungus known as Geosmithia morbida. No one knows the origin of the fungus however the beetle originates from Arizona.


  • The beetle is slightly bigger than the eye on a penny which is around 2 mm and a dark shade of reddish brown.
  • When this beetle mates and lays its eggs into the wood beneath the bark of the host tree the fungus it leaves behind kills the wood and leaves dark brown cankers where it burrows and light yellow patches on the tissue that prevents the storage as well as production of sugars to sustain the tree.
  • Some external signs of infection include yellowing as well as loss of the leaves on the branches and twigs.
  • The average time for the infected tree to die is three years but some can live up to a decade with TCD.

TCD in Canada

In the present thousand canker disease is not affecting walnut trees in Canada however it is present in the Eastern US and could spread to Southern Ontario and Quebec where the black walnut trees are concentrated.

Ecological Niche

The Walnut Twig Beetle is a consumer of walnut trees, black walnuts in particular. Since Walnut Trees are producers that make their own nutrients and the beetles get their nutrients directly from the wood of the trees that makes the beetles primary consumers. The predators of the twig beetle are the beetle larvae of other beetle species such as Madoniella dislocatus and Enoclerus nigripes that consume the twig beetles larvae.

Cause for Population Decline of Black Walnut Trees

  • Due to shipping of walnut wood that has been poorly inspected of insects the beetles have become more numerous and have started to appear East of their original home range.
  • The authorities have not found a way to effectively eradicate the beetles before they inhabit the trees and infect it with Geosmithia.

Range of Walnut Twig Beetles

The first sightings of the walnut twig beetle were in 1928 in Arizona in South Western USA taking on an Arizona Walnut Tree as a host. Recently in the last two decades the beetles have been found as far east as North Carolina and Pennsylvania and as far north as Wyoming and Idaho.

Population size of Walnut Twig Beetles

Due to the minuscule and inconspicuous size and colour of the beetle as well as factoring in its range and relative obscure nature it is not easy to calculate how many beetles there are.

Ecological Impact

Over the past 20 years thousands of black walnut trees worth up to $851 million have been destroyed by the Walnut Twig Beetle. Without the trees animals such as chipmunks, squirrels and birds that feed on the insects which themselves feed on the leaves have lost an important food source. They also act as a stabilizer for the soil to prevent it from eroding as well as a carbon sink that decreases carbon dioxide in the atmosphere and helps to slow global warming. The Black Walnut is also important in industry especially in Missouri which has the largest population of Black Walnut Trees. There it is prized for its wood that goes into making instruments, bowls and gun stocks and its walnuts which are made into ice cream and cookies.

What is being done to combat expansion of the walnut twig beetle?

In the US 16 states have placed restrictions on the shipment of walnut lumber with its bark intact 6 out of those quarantined states have been infected with TCD and 9 other states in the west. These are not the principle range of the black walnut but are introduced areas as opposed to the eastern states where all quarantines have been placed. It is possible that insecticides such as carbaryl could be applied to the trees branches in trunks in order to kill a larger number of beetles and eventually wipe them out from the east. Sadly this would kill large amounts of honeybees that pollinate the walnut flowers which would in effect prevent a new generation of walnut trees from existing.

Tree afflicted with TCD

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Range of Black Walnut Tree

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Range of Walnut Twig Beetle

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