One of the Most Aloof Sunflowers Ever! The Cowpen Daisy

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 ….. 15¹ different 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)