ID Thousand Cankers Disease

Early Detection is Key to Conrolling

Thousand cankers disease poses a deadly threat to Missouri's valuable black walnut industry. Fortunately, TCD has not yet been found in Missouri. However, early detection will be key to controlling it.

Identify TCD

Use this information to identify TCD symptoms and report evidence.

Step 1. Make sure the affected tree is a black walnut

  • Bark is rough. The surface, when lightly scraped, shows a chocolate-brown color.
  • Leaves have 13 to 23 leaflets on green stalks. Leaflets are pointed with toothed edges, and emit a strong aroma when crushed.
  • Male flowers appear in drooping catkins when leaves emerge in spring.
  • Nuts with green husks turn black as they ripen. The dark nut shell is deeply grooved.
  • Twigs are thick, light brown, with fuzzy buds and a tan, chambered pith at the core.

Step 2. Identify TCD symptoms

After confirming that the affected tree is a black walnut, determine whether signs and symptoms of TCD are present.

  • Midsummer yellowing and wilting of foliage high in the crown. Limbs die back, usually from the top downward. Leaves browned in midsummer often remain attached to twigs.
  • New sprouts may grow from roots or trunk leading to a "bushy" appearance below dead branches.
  • Dark brown cankers. Removing bark from dying limbs exposes dark brown cankers. Cutting too deeply removes cankers. TCD cankers occur only in the thin phloem layer immediately under bark in branches greater than one inch in diameter.
  • Signs of walnut twig beetles. The beetles are tiny, about the size of the letter "i" in the word "liberty" on a dime. It may be easier to find cankers and beetle tunnels under the bark than to find the beetles themselves.

Step 3. If you think you’ve found TCD symptoms, please report them!

Take photographs of the entire tree, a close-up of leaves and any other symptoms. Email photos to forest.health@mdc.mo.gov, and use the "Report Invasive Forest Pests in Missouri" link under "External Resources" below to complete your online report.

Don’t confuse TCD with other common walnut problems

Many factors besides TCD can kill or damage walnut trees. These include environmental factors, diseases and pests.

Environmental factors

  • Weather events (freeze, drought, flood or storm damage)
  • Chewing by squirrels
  • Contact with herbicides
  • A bad site (poor soil, competition with other trees, grasses and weeds)

Diseases

Anthracnose

This is a common foliar disease that can cause walnuts to start losing their leaves in midsummer. When the infected walnut leaflets fall, the bare rachis or stem they attach to often remains on the tree for a period of time. Visit the USDA’s Forest Service's walnut anthracnose page for more information.

How anthracnose differs from TCD

Anthracnose causes a rapid leaflet drop, whereas TCD-killed leaves may remain attached to branches. Anthracnose is less likely to kill tree branches.

Fusarium cankers

These are often visible without removing the bark. The elongate open cankers often start at the base of the tree and may be associated with weather fluctuations, wounds or ambrosia beetle attack. See the USDA Forest Service’s page on Fusarium cankers for more information.

How Fusarium cankers differ from TCD

Fusarium cankers are often large and visible when you look at the tree. Thousand cankers disease cankers are hidden under the bark.

Insects

Ambrosia beetles

These are tiny boring beetles that tunnel into the wood of the tree. Small cylindrical sawdust “toothpicks” protrude from their entry holes. Areas of discolored tissue may surround attack points.

How ambrosia beetles differ from walnut twig beetles

Ambrosia beetles tunnel directly into the wood of the tree rather than just under the bark, as walnut twig beetles do. See the USDA Forest Service’s page on ambrosia beetles for more information.

tcdmap10-13.jpg

map shows states where TCD has been found
States With TCD
Tennessee, which borders Missouri, is known to have TCD. View this 20-slide presentation about TCD, and learn how to identify symptoms of the disease.

vial-of-walnut-twig-beetles01-18-2011.jpg

Photo of a vial of walnut twig beetles.
Don't Accidentally Spread TCD
More than 23,000 walnut twig beetles emerged from two firewood-sized pieces of black walnut wood.

black-walnut-tree01-18-2011.jpg

black-walnut-tree
Black Walnut Tree
Black walnut trees grow up to 90 feet tall with a rounded, open crown.

black-walnut-twig-cross-section01-18-2011.jpg

black-walnut-twig-cross-section
Black Walnut Twig Cross Section
Twigs thick, light brown, with fuzzy buds and tan, chambered pith at the core of the twig.

black-walnut-leaves01-18-2011.jpg

black-walnut-leaves
Black Walnut Leaves
Leaves with 13 to 23 leaflets on green stalks. Leaflets pointed with toothed edges, strong aroma when crushed.

black-walnut-catkins01-18-2011.jpg

black-walnut-catkins
Black Walnut Catkins
Male flowers appear in drooping catkins when leaves emerge in spring.

black-walnut-bark01-18-2011.jpg

black-walnut-bark
Black Walnut Bark
Black walnut bark is rough, and when the surface is lightly scraped shows a chocolate brown color.

tiny-twig-beetle01-18-2011.jpg

Photo of tiny walnut twig beetle on face of dime
Tiny Twig Beetle
The walnut twig beetle is the size of the letter "I" in the word "LIBERTY" on the face of a dime.

midsummer-leaf-wilt01-18-2011_1.jpg

photo of walnut tree showing mid-summer leaf wilt in crown
Midsummer Leaf Wilt
One symptom of TCD is midsummer wilting of individual branches.

black-walnut-limbs-die01-18-2011.jpg

photo showing dead black walnut limbs
Black Walnut Limbs Die
Thousand cankers disease causes black walnut leaves to yellow and wilt in mid-summer. Limbs die back, usually from the top downward.

browning-black-walnut-leaves01-18-2011.jpg

Photo shows walnut tree with browning leaves
Browning Leaves Indicate TCD
In midsummer, TCD-infected trees may show wilted brown leaves on branches high in the canopy.

tcd_diagnosis_12-29-10.jpg

Photo of scientist using a drawknife to expose thousand cankers disease
Exposing Thousand Cankers Disease
Lightly scraping away the bark exposes TCD cankers underneath.

tcd-cankers01-18-2011.jpg

photo shows debarked limg revealing thousand cankers disease
TCD Cankers
This scraped limb reveals walnut twig beetle tunnels and cankers under the bark.

walnut-twig-beetles01-18-2011.jpg

walnut-twig-beetles
Walnut Twig Beetles
Tiny walnut twig beetles tunnel in the center of the cankers.

declining-black-walnut-tree01-18-2011.jpg

Photo shows declining black walnut tree
Declining Black Walnut Tree
Black walnut trees in Missouri can display die-back for many other reasons besides TCD.

anthracnose-symptoms-leaves01-18-2011.jpg

anthracnose-symptoms-leaves
Anthracnose Symptoms Leaves
Anthracnose, a foliar disease of walnuts, turns healthy leaves yellow and brown.

anthracnose-symptoms01-18-2011.jpg

Photo shows symptoms of walnut anthracnose
Anthracnose Symptoms
Anthracnose causes leaflets to drop, whereas TCD may cause entire leaves to wilt, turn brown and hang on the tree.

fusavium-cankers01-18-2011.jpg

Photo shows fusarium cankers
Fusarium Cankers
Fusarium cankers are elongated, larger than TCD cankers, and often visible without removing the bark.

ambrosia-beetle-tunnels01-18-2011.jpg

Photo of ambrosia beetle tunnels in black walnut
Ambrosia Beetle Tunnels
Unlike walnut twig beetles, ambrosia beetles tunnel down into the wood of the tree.

ambrosia-beetle-toothpicks01-18-2011.jpg

Photo shows toothpicklike sawdust structures protruding from black walnut branch
Ambrosia Beetle "Toothpicks"
Unlike walnut twig beetles, ambrosia beetles can cause sawdust “toothpicks” to protrude when they first attack a tree.

Stay in Touch with MDC

Stay in Touch with MDC news, newsletters, events, and manage your subscription

Sign up

Our Magazines

Conservationist Magazine

Our monthly publication about conservation in Missouri--free to all residents.

Missouri Conservationist Cover

Xplor Magazine for kids

Xplor helps kids find adventure in their own backyard. Free to residents of Missouri.

xplor September/October