In poorly drained soil direct contact between roots is not necessary to cause toxic reactions since juglone moves through the soil water. It has been suggested that plants having shallow root systems are more tolerant of juglone than deep-rooted species. Tolerance to juglone by shallow-rooted species may also be attributed to better drainage of soil water in upper soil levels. Other problems Horses and ponies can contract acute laminitis, an inflammation of the foot, where black walnut wood chips or sawdust is used for stall bedding. Acute laminitis and high respiratory rates in horses and ponies has also been reported where stables and paddocks are located too close to walnut trees.
Pollen shedding from walnut trees can cause allergic reactions in people and horses.
The following table lists plant species that are known to be tolerant and susceptible to juglone. This information is provided as a public service, but we cannot guarantee that the information is current or accurate. Readers should verify the information before acting on it.