I ran across some really interesting facts while I was researching something else and thought I would share!
Allelopathy (uh-lee-LOP-uh-thee) is a biological phenomenon where a plant releases chemicals that inhibit another plant’s growth or reproduction or very survival.
Allelopathy was recognized as early as 300 B.C. by Theophrastus who studied under Plato and was Aristotle’s successor in the Peripatetic school of philosophy in ancient Greece. He noticed that pigweed inhibited the growth of alfalfa. In the first century A.D. a Chinese book on agriculture and medicinal plants, the Shennong Ben Cao Jing, listed 267 plants believed to have pesticidal qualities, some with allelopathic characteristics.
The term allelopathy was first coined in 1937 by Hans Molisch, an Austrian professor, to describe plants that inhibited the growth of other plants. Later it was used in a broader sense of plants that affect another plant in any way. A lot of research has been done on allelopathy, producing a lot of disagreement as to the actual effects, since one plant can always affect another plant if they are vying for the same growing space.
However, interest has recently been renewed and much research is ongoing, mostly for agricultural purposes. Allelochemicals that plants exude are definitely real.
Think of the possibilities! Allelopathic weed management in crops would greatly reduce the need for herbicides. And what if someone could produce an allelopathic bermuda grass cultivar that would inhibit weed growth?
Did you know that the dreaded nutsedge (or nut grass,) the bane of lawn care companies and homeowners and one of the most invasive weeds in the world, has allelopathic qualities? If you think it’s a nuisance in your lawn, you should see it in crop fields, where it can significantly reduce the crop yield!
Another good example of allelopathy is the Black Walnut tree (Juglans nigra) which contains the chemical Juglone in all of its parts, although it is concentrated in the roots, nut hulls and buds. Juglone is a respiration inhibitor. Not much will grow under a walnut tree, where the roots are biggest. However, tree roots can really spread out so a walnut tree can affect plants that aren’t directly under it. A plant’s allelopathic qualities can affect some plants intensely, and others not at all.
For example, tomato plants, eggplants, apple trees, crocus, azaleas and pepper plants are very susceptible to juglone, while beets, carrots, tulips, arbor vitae, lilac, forsythia and corn are not.
Some other allelopaths are: eucalyptus, cottonwood, sassafras, black cherry, and sorghum. Sorghum is currently being researched in earnest as a weed suppressant. (Allelopaths - I feel like I’m talking about Star Trek characters…)
Anyway, the future use of allelopathy both for agriculture and other horticultural applications seems very promising! And, if a plant has allelopathic qualities, does that make it more hardy than other plants?