Cause

• A chemical, juglone, produced by trees in the walnut family causes a wiltlike condition in certain vegetables. While suspected and documented in ancient times, the phytotoxin was not discovered until the 1880s when scientists identified it in walnuts. Juglone, found in the leaves, nuts, roots and wood of walnut trees, affects plants in the root zone and under the canopy of the trees. In larger, old trees, the roots might extend beyond the crown by three times, affecting plants.
  
  

Effect

• Trees with juglone -- black walnut, pecan, butternut and Persian walnut -- cause a debilitating and often deadly effect on plants. Black walnut tends to have higher amounts of the chemical and therefore a more pronounced effect. Juglone inhibits respiration, causing sensitive plants to have yellowing and wilting. The plants eventually die as their energy needs are not met. The most-affected plants include tomatoes, asparagus, peppers, eggplants and potatoes.
  
  

Solutions

• It is possible to grow vegetables even with a walnut tree in the vicinity. Raised beds with juglone-free soil added can work for some vegetables. For success with raised beds, you will have to diligently remove any leaves and nuts that fall on the bed. The bed height should be12 or more inches above the ground to keep the vegetable roots out of the soil that has traces of juglone in it. You can also plant susceptible vegetables in containers. While tree removal is an option, the juglone will stay in the soil and the roots will continue to release it for some time. You also lose the benefits a walnut tree supplies.
  
  

Types

• The only way to guarantee a successful harvest near a walnut is to plant vegetables that juglone doesn't affect. Many common, easy-to-grow vegetables do fine near walnut trees. Some options to choose from include corn, squash, snap beans and carrots. You can incorporate melons, onions, lima beans, parsnips and beets in a juglone-affected area, as well.