Threat to American Walnut Trees

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Blog entry by John Gray posted 03-18-2009 07:39 PM 2511 reads 0 times favorited 4 comments Add to Favorites Watch

Courtesy of Fine Woodworking dot com –

Black walnut trees in the U.S. are facing a serious threat called thousand cankers disease, according to Colorado State University researchers. This recently recognized problem has already devastated black walnut trees west of the Rocky Mountains over the past 10-15 years.

The disease is caused by a newly discovered fungus that is carried to trees by the walnut twig beetle. A native of the Southwest, the beetle is usually associated with the Arizona walnut tree, to which it is not harmful. It is, however, harmful to the black walnut tree which has been planted extensively throughout the West.

“The walnut twig beetle has shown a fantastic spread through the western U.S. within the past 25 years,” says Whitney Cranshaw, an entomologist at Colorado State. “In recent years we have seen new records for this insect in Colorado, northern New Mexico, Utah, Idaho, Oregon and Washington. And everywhere we are finding the beetle, all the black walnuts are dying.”

The bigger concern is if thousand cankers disease moves east where black walnut is a common forest species. “I think thousand cankers disease has the potential to devastate black walnut just as Dutch elm disease nearly wiped out American elms and chestnut blight eliminated the American chestnut,” said Cranshaw. “Right now it is contained west of the Front Range in Colorado and the High Plains provide a good natural barrier, but all it would take is one careless individual moving a walnut log with the beetles and we could have an outbreak that could quickly spiral out of control.”

Cranshaw emphasizes the importance that foresters, arborists, woodworkers and lumber mills recognize this new threat. They say no walnut logs with bark intact should be allowed to move further east than where the disease is currently known. Walnut lumber and well-dried logs without bark likely pose little threat of carrying the fungus-carrying beetles.

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4 comments so far

View PurpLev's profile


8523 posts in 3068 days

#1 posted 03-18-2009 08:59 PM

Thanks for the post, and bringing it to people’s attention. this is a serious case, and is somewhat scary. on one hand it is mother nature’s natural case of change and evolution, and on the other hand it’s a lose of a beautiful resource.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View Julian's profile


880 posts in 2945 days

#2 posted 03-18-2009 11:09 PM

I think it’s not so much mother nature as it is mankind helping spread the disease from cutting and hauling trees. In Chicago there is a Chinese beetle, (asian longhorn beetle),that came here in untreated shipping pallets that is wiping out certain tree species.

-- Julian, Park Forest, IL

View Todd A. Clippinger's profile

Todd A. Clippinger

8901 posts in 3519 days

#3 posted 03-18-2009 11:10 PM

Thanks for sharing the article.

It is a bit scary to think of how many varieties of trees are dying off due to blight or insects. When I was working in Ohio, the big news was on the beetles destroying the ash trees.

-- Todd A. Clippinger, Montana,

View SwedishIron's profile


142 posts in 3060 days

#4 posted 03-18-2009 11:28 PM

I live just outside of Boulder, Colorado.. and I know that they recently ordered all the Walnuts to be cut down and bark stripped off and burnt if the lumber is to be made into lumber by a few authorized sawmills. Pretty scary to see a totally healthy tree die over the course of three years.
Hope this doesn’t move east… but the reality due to our highway systems and the mobility of people today.. its not a matter of if.. but when.

-- Scott, Colorado

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