ID and Report TCD Symptoms
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.
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 email@example.com, 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.
- 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)
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.
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.
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.