allelopathy – a curious nature

Part 3 ….. An Allelopath Declares Chemical Warfare

August 15, 2025

The more I learn about Cowpen Daisy (Verbesina encelioides), the more the words Intrepid (fearless and bold), Interloping (meddlesome and smothering), and Impertinent (pushy and rude) come to mind.

Cowpen Daisy is literally a plant at war …..

Its adversaries are neighboring plants …..

Its weapons of choice are chemicals ….. 15¹different Allelochemicals² to be exact.

Cowpen Daisy shows no mercy to its most susceptible victims, and given the right conditions in the right locations, Cowpen Daisy can cripple ecosystems, and unravel biodiversity.

Oh No! What Have I Done! Have I unleashed a formidable enemy to run amok, bullying its way through our mostly intact biodiverse high desert ecosystem?

Maybe not! (Spoiler alert…… Allelopathy³can be bad, but I still love this happy Daisy)

On August 6th, I received an excellent question from one of my blog followers, based on my first Cowpen Daisy post :

“Do you have any concerns about this becoming an invasive plant? Best wishes, Nancy”

In reply, I expressed my concern about the number of “seedlings coming up late spring,” and how “I was definitely alarmed and wondered about the need for early control.” Fortunately, “as the season advanced, it became clear the density of plants seemed self-controlling.” Based on my limited experience with Cowpen Daisy, I explained how during the summer of 2023 “the plant completely covered an extremely large field near our home,” causing me concern about its invasive tendencies. But upon “[R]eturning the following year (2024) and again this past spring (2025) to see if the same field was blanketed again in these plants, “I couldn’t find a single Cowpen Daisy anywhere! So no, this annual [doesn’t appear to be] “invasive, at least not in central New Mexico.”

But Nancy’s question prompted me to dig deeper into on-line research. I wondered: Is Cowpen Daisy invasive outside of its native range, particularly where conditions are ideal for its aggressive growth? Yes, it is! And its invasiveness is further enhanced where neighboring plants are susceptible to the impacts of the allelochemicals released by Cowpen Daisy’s leaves, roots and decaying leaf matter in the soil.

One example where Cowpen Daisy is an introduced species and has become invasive is in India. Fields of mung bean, corn, chickpeas, and sweet melon are being outcompeted by invasive stands of Cowpen Daisies. These food crops are severely impacted by two allelochemicals released by the both roots and leaves of the Daisy; steroids and phenols. Studies of these four crops demonstrated not only “the suppression of germination and growth in these plants” but “also revealed an antagonistic effect on [their] chlorophylls, carotenoids and protein levels.” In other words, Cowpen Daisy is winning the war against India’s mung bean, corn, chickpea and melon crops, and farmers are currently engaged in a battle to develop a strategy of control and run this biological enemy out of their country.

Cowpen Daisy is only considered a native species to the Southwest U.S. and Northern Mexico. However, it has been introduced (either intentionally or by accident) and is considered naturalized in parts of Eastern North America, the Middle East, Spain, Argentina, Australia and the Pacific islands. As such, Cowpen Daisy’s nature to drop allelochemicals everywhere it grows allows it to behave like an invasive plant in countries where it is naturalized. Without diligent management (via herbicide application or mechanical control), it can thrive to the detriment of their desirable plant species’ survival.

Have I defeated my goal of reestablishing a diverse native plant community in disturbed areas surrounding our new home? “Not likely,” says I, optimistically! In addition to Cowpen Daisy, the variety of native plant species I intentionally seeded last fall and early this past spring, have germinated, grown, flowered and seeded or are in the process of flowering and seeding, most of which are adjacent to a Daisy. Of course time will tell. Meanwhile, I’ve declared this to be a happy ending to this post and my stand of happy Cowpen Daisies! However ……. next spring, if germination rates from my reseeders are low or zero, but Cowpen Daisy returns with renewed vigor, then I have a control job waiting for me. And the best advice I’ve read is to “pull out old plants and roots and selectively remove new seedlings.” That’s acceptable! That I can do!

Until then!

Do you struggle with weedy, invasive plant species in your garden or yard? Have you seen fields of blooming weeds and wondered …… “what weed is that?” Do you know the names of those pesty plants and do they seem to keep your favorite variety of cucumbers from growing? It might be interesting to learn if your local invasives are one of the many Allelopaths happily growing in our world! Let me know!

As always, thanks for dropping by!

¹Cowpen Daisy is known to release up to 15 different allelochemicals² from its leaves and roots, such as guanidine, phytosterols, phenolic acids, tripertenes, flavonoids, dicarboxylic acids, phytophenols, steroids, phenols, and others. Fresh and decaying leaf litter leach 14 of those allelochemicals into the soil.

^2,3Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the germination, growth, survival, and reproduction of other organisms. These biochemicals are known as allelochemicals and can have beneficial (positive allelopathy) or detrimental (negative allelopathy) effects on the target organisms and the community. Allelopathy is often used narrowly to describe chemically-mediated competition between plants. Allelopathic interactions are an important factor in determining species distribution and abundance within plant communities, and are also thought to be important in the success of many invasive plants. (source: Wikipedia)

Part 1 ….. Can There Be Too Many Sunflowers?

August 5, 2025

It was the Fall of 2024. A small cluster of Cowpen Daisies (Verbesina encelioides) flourishing on the severely disturbed ground surrounding our new home was going to seed. Waiting several weeks until the migratory birds ate their fill, I spent an hour or so collecting as many remaining dried seeds (cypselas) as possible, stuffing full two quart-sized ziplock bags. About 1/3 of the seeds I scattered around the house where they would overwinter on the ground. The rest were poured into large pill vials that were labeled with species name, location, and date, then placed in the refrigerator to simulate cold storage until Spring.

Cowpen Daisy cypselas (seeds) 08/04/2025 at Punch

It was late April 2025. The chances of heavy frost seemed a distant memory. My fingers crossed, I chose a sunny 42 degree morning to liberate those refrigerated seeds from 6 months of cold storage, and scattered them in disturbed areas not seeded last Fall. Then I waited like an expectant parent, watching for signs of germination, worrying that runoff from late season snows might wash away my scattered seeds, expecting that flocks of migratory birds would gobble them all up, and hoping for gentle rain showers to swell those thousands of seed coats to aid those tiny embryos in growing their first roots (radicles) and first leaves (cotyledons).

Then early June 2025. Success! Cotyledons were literally popping up everywhere, which meant the radicles were already expanding into the soil. They were especially crowded where I’d scattered all the cold storage seeds, and germination was obvious where seeds had been scattered the Fall of 2024. By early July, those Cowpen daisies were crowding out many of the other native species I’d also seeded in the same areas.

Backyard and overflow Cowpen Daisies, robust growth after Fall 2024 seeding (08/03/2025)

And now it’s early August 2025, and what a dazzling show! Even though the sunflower yellow flowers of Cowpen Daisy are small (2” wide), there are up to 75 long-stemmed flowers on each plant that can grow from 4-5’ tall! They are so dense, the backyard fence is hardly visible, our walking paths are totally draped with 4” long leaves, and if there’s a rattlesnake lurking around under our massive Cowpen Daisy canopy, we’d probably (hopefully) hear him well before he slithered into view!

Goals and Lessons Learned

I’ve learned a lot by parenting these Daisies; from the best time to scatter seed (in the late Spring following cold storage) and where (not so close to other desirable natives or pathways), to managing the mass of growth (by organizing through selective removal). Our initial goal of seeding and growing native plant species was to attract and help feed wildlife (pollinators, reptiles, rodents, birds and mammals), and we are optimistic that achieving this goal long-term seems realistic with the success we’ve had to date. However, because so many of our native plants are losing the battle against habitat loss caused by invasive species encroachment and takeover, land development, and climate change, we will continue to explore ideas to expand our initial goal to address the habitat situation. As we gain insight about the best native plants to grow to help restore our disturbed soils, we will learn and share with our neighbors those species that: are drought tolerant; aid in building soils; are effective at invasive weed suppression; provide wildlife benefits; and increase plant diversity.

Cowpen Daisy and pollinator 08/01/2025 at Punch

Happy – Happy – Happy! Will I be collecting Cowpen Daisy seed again this Fall? You bet! Having all that sunshine yellow around our home is thrilling. Every morning all those thousands of sunflower faces looking East towards a new day are about the happiest sight ever! And having such wild, uninhibited growth of a native annual out our back door has been ideal for observing the pollinators that benefit from the abundant nectar and pollen, enjoying the aerial acrobatics of several phoebe families that have been feasting on those pollinators, and promises to be a perfect spot for bird watching this Fall when all those cypselas ripen into high protein food.

Can’t wait!

Do you ‘know’ a special native plant? How about a native butterfly garden? Are you a bird watcher? Maybe you enjoy the occasional deer, coyote, or bobcat wander through your yard? Please share your favorite wildlife encounter!

As always, thanks for stopping by!

Tag Archives: allelopathy

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