Ragweed renegades

The disheartening knowledge that a fall cooling is still weeks away is only mitigated by knowing the autumn allergy season will arrive with the moderating temperatures. Given the substantial and consistent rains during the summer of 2018, the growth and expansion of sneeze-inducing weeds has been tremendous.
Chief among these offenders is common ragweed (Ambrosia artemisiifolia), an herbaceous plant in the Asteraceae family native to North America. Its capabilities to induce all the negative hay fever symptoms far exceed its reputation as a poster plant for tissue paper sales.
Curiously goldenrod, the common early autumn wildflower, is often blamed for the onset of sneezing, itchy and watering eyes. In reality, it is guilt by association for the highly visible goldenrods.
Unfortunately, at least for the goldenrod, both bloom at the same time and goldenrods’ flowers are much easier to see and blame. For the record, Goldenrod pollen is too heavy and sticky to be blown far from the flowers, and if there is an allergic reaction the unlucky person must have had very close contact with the bright yellow blooms before symptoms begin.
Common ragweed, and there are other species besides the common, is most often found in disturbed habitats such as cultivated fields, orchards, home or commercial landscapes and roadsides. In Jefferson County, it is especially abundant along ditch banks where its seeds are easily disbursed by wind and water.
Common ragweed growing in home landscapes will compete with shrubs for light, moisture, nutrients, and space which results in significant performance losses from preferred shrubs. This native nuisance can rapidly grow to more than seven feet height and dominate companion plants.
A prolific seed producer, it is capable of producing up to 62,000 seeds per plant when growing under ideal conditions. Even worse, these seeds can remain viable for many years in undisturbed soil.
Dormant seed of this species requires a period of exposure to cold temperatures to germinate. Germination is optimal in the spring at soil temperatures of 50 to 80 degrees Fahrenheit.
Temperatures above 86 degrees will halt germination and send the seeds back to dormancy. After a repeat of the chilling requirement the following winter germination will begin again.
The mature plants are erect and branching with a shallow taproot which produces a fibrous root system. Stems are green to purple with long rough hairs which are usually obscured from view by the medium green colored leaves.
The leaves are compound, deeply lobed, and usually much wider at the base than the tip. Mature leaves are mostly hairless, but small leaves often have hairs on the underside.
Inconspicuous small, about an eighth of an inch, the green male and female flowers are present on separate heads on the same plant. Male flowers are at the top of the plant and usually drooping with the female flowers in the center of the upper leaves and branches.
Individual plants produce in excess of one billion wind-dispersed pollen grains, too many of which make it to the noses of Jefferson County residents.
This plant can be controlled in landscapes with mowing and over-the-counter herbicides, but with 2018’s bumper crop sporadic control efforts may offer little relief to sinus sufferers.
As the old saying goes, misery loves company so buy an extra box of tissue to share with others affected by common ragweed induced hay fever.
To learn more about common ragweed, contact the UF/IFAS Jefferson County Extension Office at (850) 926-3931 or Jefferson.ifas.ufl.edu