Issue 4, June 8, 2022

ALLELOPATHY: A Plant’s Chemical Warfare

When I think of plants that can defend themselves from pests, I think of thorns on roses or a venus fly trap, but not necessarily a black walnut tree? Besides the potential nut falling onto my head, they can pack a powerful punch on other plants. Some plants can inhibit the growth of another. This biological process is called allelopathy. Allelopathy refers to one plant's beneficial or harmful effects on another from the release of biochemicals called Allelochemicals. These allelochemicals can be used as growth regulators, herbicides, insecticides, and antimicrobial crop protection products.   

The term allelopathy is from the Greek-derived compounds allelo and pathy (meaning “mutual harm” or “suffering”). Gardeners and farmers have used allelopathy for many years. Allelochemicals can significantly affect the growth of other plants in good or bad ways. For example, when using straw mulch, the allelopathic chemicals from the decomposed straw act as a weed suppressant. French type (Tagetes patula) marigolds release a chemical in the soil, preventing root-knot nematode eggs from hatching. Sunflower, walnut, and sorghum can suppress many plants from growing near them, leaving them nearly weed-free. They can release these chemicals even in decomposition, making them a good mulch.

Common plants with allelopathic properties include
Red maple
Golden Rod
Garlic mustard
Tall Fescue
Kentucky bluegrass

Now that you understand what allelopathy is, search for those plants and allelopathic as you begin to plant your garden or flower bed. This will allow you to know more about that plant and if it has those properties. A concern is that some of the allelochemicals in the decomposition of plants can be persistent, so should you notice a continual decline in your plants, you might want to remove the mulch. Composting that plant material will deactivate those residues.  

Allelopathic plants use this process to survive in nature and reduce competition from nearby plants. This can mean that allelopathy can play an essential role in farming systems to control weeds, diseases, and insects. The allelochemicals are environmentally friendly and can have a great value in sustainable agriculture. There is still a lot more research to know about allelopathic plants and their properties.

Maria Turner

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