Things You'll Need
Black walnuts are sometimes known as "killer trees." Although some farmers grow stands of black walnut for wood that can produce long, straight boards and material for furniture, the trees also produce a chemical called juglone. In your landscape, juglone can poison the soil and prevent other plants from growing near the tree. If you want to rid yourself of a walnut tree, cutting it down may not be enough. Surviving walnut roots can still produce juglone and kill other plants. Instead, you must completely kill the tree. One way to do this is to girdle the walnut tree's trunk.
Mark a spot on your tree at a point 4 feet above the ground using chalk and a measuring tape. The chalk will help to guide you when you girdle the tree.
Cut a ring through the bark and into the tree using a hatchet. This ring should be about 2 inches wide and 2 inches deep. A tree such as a walnut has its vascular system within the bark. By cutting the ring through the bark, you will interrupt the tree's vascular system and slowly kill the tree.
Cut a second ring into the bark at a point on the tree's trunk 4 inches above the first.
Spray the trunk over the girdling marks with a product containing glyphosate. Glyphosate is a systemic herbicide. When you use glyphosate, the walnut will pull the herbicide into the rest of its system, which will kill the roots of the walnut tree.
Remove the walnut tree by cutting it down after it is dead. Signs that a walnut tree has died include the wood under the bark turning gray, the leaves turning brown and falling from the tree and the twigs becoming brittle and easily snapping.
- University of Minnesota Extension: A Practitioner's Guide to Stem Girdling Roots of Trees
- Ohio State University Extension: Controlling Undesirable Trees, Shrubs, and Vines in Your Woodland
- Iowa State University Extension: Black Walnut: The Killer Tree
- Purdue University Extension: Black Walnut Toxicity
Tracy Morris has been a freelance writer since 2000. She has published novels and numerous online articles. Her work has appeared in national magazines and newspapers including "Ferrets," "CatFancy," "Lexington Herald Leader" and "The Tulsa World." She holds a Bachelor of Arts in journalism from the University of Arkansas.