Black Walnut Toxicity

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Black walnuts can create wilting symptoms in many plants including tomato, potato, alfalfa, and other herbaceous and woody plants. This problem is caused by a chemical called juglone. It is produced by several species of trees in the walnut family, including black walnut, Persian walnut, butternut, and pecan.

The symptoms of walnut wilt include wilting and eventual death in early to mid-summer. Plants growing further away may not die, but show signs of being stunted. One distinct symptom of walnut wilt is the presence of inner stem tissue turning brown. If walnut trees are located nearby, then juglone toxicity from walnuts is probably to blame.

Juglone is a highly reactive chemical, making it quickly inactivated in the soil. It is released into the soil from leaves, nuts, and roots. Most uptake of the toxin occurs when susceptible plants uptake juglone from nearby walnut roots.

To prevent walnut wilt, locate susceptible tomatoes, potatoes, apples, lilac, asparagus, and chrysanthemums, among others, away from walnut trees. If this is not possible, removal of walnut trees may be the only option. You must wait at least two years before planting tomatoes where walnut trees once were. Juglone can persist in tree roots for extended periods.

Related Information: Walnut Wilt, www.oznet.ksu.edu

Lynn Loughary, LLoughar@oznet.ksu.edu
County Extension Agent, Horticulture
Wyandotte County, Kansas
Kansas State University Research and Extension