Walnut trees

Fig. 2. Toxic compounds found in cashew nuts (8 and 9) and in walnuts and walnut trees (10 and 11). See text.

Walnuss, /. walnut, -baum, m. walnut tree Juglane species, esp. J. regia) (grauer) butternut tree J. cinerea) (weisser) hickory (Hicoria sp.). 

Davis (19) in 1940 extracted and purified the toxic substance frcm the hulls and roots of walnut (JugIans) and found it to be identical to juglone (5-hydroxy-l,4-naphthoquinone). This compound proved to be a powerful toxin when injected into the stems of tomato, potato and alfalfa plants. The allelopathic action in the case of juglone (walnut tree and its vicinity) is well established. 

The walnut tree produces wood that is used for countless purposes, and is considered the finest wood in the world. The wood is easy to work with, yet it is very hard and durable—and when it is polished, it produces a rich, dark luster. It also shrinks and swells less than any other wood, which makes it especially desirable for fine furniture, flooring, and even gun stocks. 

Walnut trees exude a chemical into the soil near their roots which can be poisonous to some trees and shrubs. Fruit trees, for example, will not survive if planted too close to a walnut. Many other plants, such as maple trees or ivy, are not affected by the walnut s presence, and are well-suited to grow in its vicinity. 

It is known that black walnut trees produce a substance that inhibits growth and causes wilting of many plants. Avoid planting vegetables, especially tomatoes, near black walnut trees. 

Ouglone is the only quinone identified as an allelopathic compound from higher plants (5). It is produced by walnut trees and is a potent inhibitor. Numerous antibiotics produced by microorganisms are quinones, including the tetracycline antibiotics such as aureomycin (80). 

Allelopathic Interference of Black Walnut Trees with Nitrogen-Fixing Plants in Mixed Plantings... 

Soil samples were collected in mid-November at a distance of 0.9 m from each walnut tree at depths of 0-8, 8-16, and 16-30 cm for juglone estimates. Special effort was taken to avoid locating sample plots near dead or declining European alder trees. Another set of samples was collected at 0.9 m from walnut trees in the same plots at depths of 0-4, 4-8, 8-16, and 16-24 cm for Nitrobacter and Nitrosomonas counts. 

Brooks, M. G. "Effects of Black Walnut Trees and Their Products on Other Vegetation" West Va. Univ. Agric. Exp. Stn. Bull. 347, 1951, p. 31. 

Researchers at UC Davis are investigating the possibility of genetically engineering the rootstock of the walnut tree with a piece of DNA that would silence an essential gene that the nematode needed for its survival (box 12.1). The idea is that the when the nematode sips on the cell it will also suck in this silencing construct. A few hours later, the nematodes will die (V. Williamson, personal communication. Sept. 5, 2006). If this approach works, then an English scion could be grafted to... 

It is well known that vegetables such as tomatoes or lettuce do not thrive near walnut trees. Juglone and a few related compounds are responsible for this effect. At a concentration of 0.002%, juglone completely prevents germination of lettuce seeds. It is thought that rain wash from walnut leaves and exudation from roots transport juglone to the soil (Soderquist 1979 Terzi et al. 2003 Terzi 2008). 

Walnut (nux juglandes) is harvested from walnut tree Juglans regia) and is the most popular nut ingredient in North American cooking. Over 30 varieties of walnut trees are currently harvested that have been developed for various characteristics including pest tolerance, early/late harvest, and shell thickness. The major walnut-producing nations are the United States (California), China, Turkey, India, France, Italy, and Chile (39). 

Older leaves yellow shoots or whole plant wilts. Cause Walnut. Fusarium, or Verticil-lium wilt. Walnut wilt occurs in soil containing black walnut roots, which secrete a substance that is toxic to many kinds of plants. Tomatoes within 50 of black walnut trees or stumps wilt and die suddenly. The toxic compound remains in the soil for some years after trees are cut down. Plant your tomatoes at least 50 from walnut trees. If this is impossible, grow tomatoes in containers in a good organic potting mix. 

Some plants are allelopathic, which means they inhibit the growth of plants growing nearby. Their roots secrete substances that are toxic to a wide range of other plants. For example, a shallow-plowed cover crop of rye will inhibit the germination of small-seeded plants and weeds. Yellow and giant foxtail, nutsedge, quackgrass, sunflowers, and walnut trees all have allelopathic properties. Keep these rela-... 

Mass trapping works best if your orchard is isolated from other sources of codling moth and other fruit pests (at least 1 mile away from other apple, pear, or walnut trees), since new pests migrate from neighboring orchards. 

Hydrastis canadensis golden seal - Hypericum perforatum St. John s wort - Juglans regia walnut tree - Matricaria chamomilla German chamomile - Myrrha myrrh (with... 

Juglone, a dye known for centuries, is produced from the husks of hlack walnuts. It is also a natural herbicide (weed killer) that kills off competitive plants around the black walnut tree but does not affect grass and other noncompetitive plants. The formula for juglone is C QHg03. 

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