Extension Spotlight

Why does a walnut produce a chemical, juglone or hydrox juglone? This is a naturally occurring chemical that is a defense mechanism protecting the walnut tree from surrounding plants. What happens to the surrounding plants? It stunts the growth of surrounding plants. Juglone inhibits plant respiration. If there are sensitive plants under a walnut, the juglone will deprive these plants of water and nutrient uptake. Symptoms such as wilting or yellowing leaves occur.

Juglone is not soluble in water. Consequently, it does not move very far in the soil. If sensitive plants are under the walnut and...