Noxious Summer Weeds Arrive Early

A heat wave has descended and summer has barely begun. After a particularly hot early spring, followed by a few days of cool bliss (for Florida anyway), we are now in the throes of high temperatures, afternoon rain, and scores of biting flies. No mosquitoes yet, though.

The weather had previously been so dry that the garden required daily water just to keep the vegetables and herbs alive. The dust was so oppressive, and even the dog, usually the consummate bundle of energy, flopped down in the shade after a few minutes of play.
During our constant caretaking of ten wild Florida acres, we have begun to notice that the sandspur (Cenchrus echinatus) and ragweed (Ambrosia artemisiiolia), which typically emerge during the later summer months, are starting to show up around the property.

Some climate researchers have pointed out that over the past 30 years spring has slowly been arriving earlier and earlier, and now typically begins 10 to 15 days before the official calendar date. Warmer temperatures and increased levels of carbon dioxide are increasing both the potency and growing season for plants, particularly weedy plants. Higher carbon-dioxide levels have “a disproportionate effect on weeds,” according to Paul Epstein, associate director of the Center for Health and the Global Environment at Harvard Medical School.

While increases in CO2 levels may be good for plants in general, there may be a downside: noxious weeds become more abundant, emerge sooner in the season, and produce more potent pollen. “It is the opportunistic plants like poison ivy and ragweed that thrive. These species are gaining a foothold because of carbon dioxide,” Epstein told WebMD in an article by Salynn Boyles. We concur with Dr. Epstein based on our observations: We shouldn’t be pulling ragweed this early in the season!

Ambrosia artemisiifolia (common ragweed)
Common ragweed (A. artemisiifolia) has a history of medicinal use, although so many people are allergic to the pollen that you are cautioned to use it with care, particularly avoiding internal use unless you are certain that you have no allergic reaction. This annual member of the Asteraceae family grows to 5 feet tall and has deeply dissected opposite leaves. The barely noticeable flower heads form on drooping spikes. Goldenrod (Solidago sp) flowers at the same time and is often erroneously blamed for the rampant allergies during hay fever season.

A. artemisiifolia is most common throughout Florida, while A. hispida (coastal ragweed) is found mostly is south Florida and A. trifida (giant ragweed) is found in widely divergent but isolated areas of state and can grow as high as 15 feet. The opposite leaves (becoming alternate higher on the stem) can be 3-lobed, 5-lobed, or entire,and the flowers form like those of A. artemisiifolia.

Anthropological evidence indicates that A. trifida seeds may have been used as medicine, but no conclusive evidence has been found for this assumption. The flower heads when crushed produce a red dye, and the leaves can be used for a green dye. (Austin 2004)

The Cherokee people, according to Austin, rubbed the leaves of A. trifida on insect stings and hives, used the juice for infected toes, and drank a leaf infusion to reduce fever and to treat pneumonia. An astringent tea of A. artemisiifolia leaves was used for fevers, nausea, mucous discharges, and intestinal cramping. The root was used for menstrual issues (Foster and Duke). Austin cites Millspaugh as indicating that the juice was helpful for treating poison ivy, but beware if you are allergic, you may end up with double trouble! A research paper (Chalchat et. al) suggests that an essential oil of A. artemisiifolia has antibacterial and antifungal compounds.

I try to look at all the plants around me as possible allies. Some are foreboding in their protection and armament such as sandspur (Cenchrus echinatus) a member of the Poaceae (Grass) family. Southern sandspur is annoying plant, especially in this sandhill habitat. Once the stalks emerge and the burs form, you find these sharp clinging fruits (even though they are still green) grabbing a hold of your clothing, your skin, or anything else that brushes past them, including the dog. They are difficult to remove and often cause secondary pain when you try to pull them off clothing or animals (using tweezers or duct tape is helpful).

In the autumn when they dry up, watch out as they are even meaner. And when they drop to the ground, you may find them embedded in your feet if you imprudently take a romp around the property barefoot. Invariably the burs end up between the dog’s paws, which he presents for extraction.

The species that grow in Florida do not have any medicinal or edible use (at least that I can find), but the liquid from the shoots, leaves, and roots of C. calyculatus (called Ka-mano-mano) was used by indigenous Hawaiian to treat deep cuts. The same parts were also used for swollen glands (scrofula) associated with tuberculosis (Moerman 1998).

In the meantime, I do my best to patiently pull up sandspur each season, hoping that little by little, the area around our house will become a more pleasant place to stroll. If someone knows of medicinal uses for sandspur, please let me know!

Further Reading

  • Austin, D. 2004. Florida Ethnobotany. Boca Raton, FL: CRC Press.
  • Chalchat, Jean-Claude, Maksimovic, Zoran A, Petrovic, Silvana D, Gorunovic, Momcilo S, et. al. 2004. “Chemical Composition and Antimicrobial Activity of Ambrosia artemisiifolia L. Essential Oil.” Journal of Essential Oil Research. Accessed online 6-8-08,
  • Foster, S. and Duke, J. 1990. Eastern/Central Medicinal Plants. New York: Houghton-Mifflin.
  • Millsaugh, C. F. 1892. American Medicinal Plants. Reprint 1974. New York: Dover.
  • Moerman, D. E. 1998. Native American Ethnobotany. Portland OR: Timber Press Inc.
  • Ziska, L. H., K. George, D. A. Frenz. 2007. “Establishment and Persistence of Common Ragweed (Ambrosia artemisiifolia L.) in Disturbed Soil as a Function of an Urban-Rural Macro-Environment.” Global Change Biology 13 (1), 266–274.

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