Black walnut trees in peril from thousand cankers disease

Walnut twig beetle (Kathy Keatley Garvey | UC Davis)

Walnut twig beetle (Kathy Keatley Garvey | UC Davis)

Citizen scientists (that could be you and me), look up at the black walnut’s leaves! At the recent meeting of the New York Nut Growers’ Association (, Karen Snover-Clift of Cornell University went over the ins and outs of “thousand cankers disease of walnut.”

Like Dutch elm disease (which pretty much wiped out American elms, once valued for creating a cathedral effect as their branches arched over tree-lined streets), thousand cankers disease is spread by an insect. But the walnut twig beetle is only part of the problem. When it bores into the bark, it spreads a fungus that clogs up a tree’s “tubes.”

With Dutch elm disease, once a tree is infected, the fungal culprit spreads within the tree to kill it. Not so with thousand cankers disease. With this disease, death comes from fungal infection that follows thousands of dark, dead cankers of insect feeding.

Who cares about black walnuts? I do. Each fall the trees bear an abundance of nutritious and delicious nuts. (Not delicious to everyone; the strong flavor does not appeal to everyone. But there’s no reason that any food should appeal to everyone, unless you’re MacDonald’s.) And, quoting from The Tree Book, written in 1914 by Julia Rogers, “The black walnut is majestic as a shade tree – a noble ornament to parks and pleasure grounds. It needs room and distance to show its luxuriant crown and stately trunk to advantage. Then no tree excels it.”

And finally, black walnut yields among the most beautiful of woods for furniture and gunstocks. Again quoting Rogers, the wood has “silvery grain, rich violet-purple tones in the brown heartwood [and] exquisite shading of its curly veinings.”

Thousand cankers disease moved into the southwestern US from Mexico (Would a wall keep them out? Will Mexico pay for it?) and has remained mostly in that region. Black walnut is native to the eastern US, but the tree has occasionally been planted out west. More importantly, the disease has recently reared its ugly head at a few locations in the east. If infected trees can be identified, the disease can be contained to check its spread.

Any tree with an infected branch is usually dead by the end of the season! So look up, scan the tops of any black walnut trees for limbs that are dead or show flagging foliage. Your job, and my job, is to look for these trees and then report them.

For a more thorough treatment of thousand cankers disease, as well as reporting guidelines, see A good start in confirming the disease would be to take some good digital photos and send them to the state diagnostic laboratory, the county Cooperative Extension office or Department of Environmental Conservation.

I find chipmunks cute, as I’m sure everybody would – except for anyone for whom the chipmunk is a garden pest. This year, for some reason, an especially good crop of chipmunks is scurrying about. I see them everywhere, except on my farmden. Their absence here could be attributed to my dog friends Sammy and Scooter and my cat friend Gracie.

I would not tolerate chipmunks if they were to eat my blueberries, my filbert nuts, my…pretty much anything that I’ve painstakingly planted and nurtured. Besides dogs and cats, traps also are effective.

As if plants didn’t have enough pest problems: I recently attacked my strawberry bed with my scythe, swinging the sharp blade low enough to cut off every last leaf from the plants. No, I’m not just another plant pest, trying to kill plants; I was “renovating” the bed, preparing it for next spring.

Shearing off the leaves not only removes leaves, but also disease spores on the leaves that inevitably find their way into any strawberry bed. Obviously, I raked up the old leaves and carted them over to the compost pile.

The next step in renovation was to pull out any weeds in the bed. The major weed in the bed was…strawberries. Strawberries spread by creeping stems, along which grow new plants that take root, making them usually their own worst weed. Each plant needs about a square foot of elbow room to realize its full potential of one quart of berries per plant.

So I ruthlessly ripped out enough plants so that my three-foot-wide bed was left with a double row of plants spaced a foot apart. Older plants get decrepit with age, so those were the first to go.

Finally, icing on the cake: I laid a one-inch depth of compost all over the bed and tucked it to each of the remaining leafless strawberry crowns. A little fertilizer and straw, pine needles, wood shavings or any other weed-free organic material would be almost as good.

It’s been a few days and already new leaves are sprouting. The plants are on their way to a healthful and healthy crop of sweet, juicy berries next spring.

To keep the earth’s average temperature from rising more than two degrees, reducing emissions from fossil fuels is not enough. Take carbon out of the air – and put it in the soil where it serves as organic matter, feeds crops, holds moisture and reduces runoff and erosion.

See “carbon farming” in action at Four Winds Farm at 158 Marabac Road in Gardiner on August 23 from 1 to 4 p.m. Jay and Polly Armour have, for 20 years, been practicing techniques that keep carbon in the soil by eliminating tillage. Come to learn and share your best ideas for ways that organic practices can mitigate climate change. Registration fees for this NOFA-NY-sponsored event are $15 per person or $25 for two or more people/farm. To register, visit the NOFA-NY event website or call (585) 271-1979.


Any gardening questions? E-mail Lee at [email protected] and he’ll try answering them directly or in his Almanac Weekly column. To read Lee’s previous “Gardener’s Notebook” columns, visit our website at

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