[2] In 1921, a study observed that tomato plants near black walnut trees exhibited wilted leaves, suggesting an adverse interaction.

[7] In 1942 it was demonstrated that tomato and alfalfa germination and seedling growth were inhibited by contact with pieces of walnut roots, providing additional scientific evidence of juglone's phytotoxicity.

The evidence that hydroxyjuglone is readily degraded is most apparent in the color change of walnut hulls from yellow to black after being freshly cut.

[14] Indigenous bacteria found in the soil of black walnut roots, most notably Pseudomonas putida J1, are able to metabolize juglone and use it as their primary source of energy and carbon.

[19][20] In addition to these inhibitions, juglone has been shown to alter the relationship between plants and water because of its effect on stomatal functioning.

Research has shown that juglone affects the yield of maize crops; however, the practice of pruning and usage of root barriers greatly reduce these effects.

[22] Some plants and trees are resistant to juglone including some species of maple (Acer), birch (Betula), and beech (Fagus).

It has also shown anthelmintic (expelling parasitic worms) activity on mature and immature Hymenolepis nana in mice.

Because of its tendency to create dark orange-brown stains, juglone has also found use as a coloring agent for foods and cosmetics, such as hair dyes.