If you use herbicides, you are merely a living being. But, if you use herbicides to make your world more lovely—in your eyes, or in the eyes of the Joneses who live next door—you are a human being.

Do you have a walnut tree, or an evergreen tree such as a spruce? Have you noticed that you have a tough time getting plants to grow under these trees? This difficulty is actually caused by the spruce or walnut producing and using "herbicides." The technical term for when plants treat other plants with herbicides is allelopathy.

One interesting facet of the production of allelochemicals is that they are termed "secondary metabolites." Usually when I discuss plant ecology, my mindset is limited: I only think of plants as "producers." In other words, plants use chlorophyll to produce sugar from air and water—so they can feed other living things. So I end up thinking only of plant metabolism for the purpose of building the plant. But the notion of secondary metabolites broadens the scope of my thinking. For example, plants also produce colors, fragrances, and fruits in order to become attractive to pollinators or for the purpose of seed dispersal. In other words, plants are attempting to out-reproduce their competitors. And with allelochemicals, plants produce them to suppress their competitors.

In baseball terms, the Astros don't just practice baseball, they scout young players to draft well. And they steal signs to disarm their opponents.

So plants use allelopathy not just to get a leg up on their competition. They use it to put the competition's legs down. Allelochemicals enter the playing field from a plant's leaves or roots. (Think about the piles of needles under the spruce tree: What can grow in there?) The leaves either emit the chemicals through the air, or the chemicals wash off the leaves from rain or dew, or the chemicals enter the soil when the leaves fall. Roots release their chemical warfare similarly. And who gets attacked? Flora and fauna: Other plants' seeds either fail to grow, or their growth is stunted. The small creatures of the soil stay away, or the large creatures take a pass on browsing. And technically, allelopathy also applies to beneficial effects. Sometimes the chemicals enhance the growth of some types of plants while suppressing others. Researchers are currently trying to replicate these chemicals to improve fertilizers and herbicides.

This brings us to the garden. It is easy to see how allelopathy relates to competition in terms of the survival of the fittest. However, the human legacy includes large-scale manufacturing not only fertilizers for better food production, but also of poisons designed to eliminate dandelions. We want to create monocultures of "lawns" not for our survival, but for our pleasure. And so the poison marketplace buzzes with each new spring.

Joshua Arp is an ISA-certified municipal specialist, Clarks Summit's municipal arborist and an operator of an organic lawn and landscape maintenance business. Reach him at josarhuap@aol.com.

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