Tomato Wilt Caused by Black Walnut Trees (6269)

Have your previously successful garden plants wilted and died all of a sudden this year? This may seem perplexing when the problem affects some, but not all, types of vegetable and flower species.

Do you have a black walnut or butternut tree in the area? If you do, the tree or trees may be causing the problem.

Black walnut and butternut produce a toxic substance called juglone in their roots, leaves, and fruit. The juglone is toxic to many plant species. Your plants may not have died in previous years because the tree's roots had not yet reached the plant roots in your garden. This year, it may be that the black walnut or butternut roots reached the susceptible garden plants' roots, and damage occurred.

The susceptible plant takes in the juglone toxin through its root system. This causes leaves to turn yellow, wilt, and then die. Black walnut and butternut tree roots can extend a considerable distance. They commonly reach out beyond the tree's drip line.

What plants are susceptible to this type of injury? Although researchers don't know all the plants affected by juglone, evidence shows that juglone most commonly poisons potatoes and tomatoes. Other susceptible plants include some apple varieties, eggplant, pepper, beans, cucumber, rhododendron, white and red pine, white birch, cinquefoil, and cotoneaster.

Black raspberry plants thrive around black walnuts and butternuts, while the closely related blackberry quickly dies.

Controlling the problem is not easy. Planting shallow-rooted species like lettuce and spinach near walnut trees reduces the problem somewhat. Cutting down the nut trees will eventually solve the problem once all the roots disintegrate completely. This may take 1_5 years, depending on the size and amount of walnut roots in your garden.

A steel or concrete barrier placed into the ground between the tree and susceptible species can help if you do this before the roots reach that point.

Because the juglone is present in all the tree parts, do not use the leaves, walnut husks, or shells as mulch for a flower or vegetable garden.

For more information on this subject, Please visit the College of Agricultural Sciences Publications Web site.

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