RAGWEED SEASON IS HERE!

 September 7, 2023

Ragweed, a common, invasive, unspecialized weed-pest, which like the human species, survives and thrives on its fecundity and invasiveness. 

Ragweed (Ambrosia artemisiifolia) is a native, annual plant which grows to almost a meter (3 ft) tall and which, due to its rapid growth, seems to appear as if by magic in late summer.  Its leaves are  characteristic and set it apart.  The often 3-6 inch long, lance-shaped (in outline) “toothy looking”leaves are wider at the base than at the tip and are deeply lobed. When grown in the shade the leaves take on a fern-like appearance. In general, viewed from a distance they do give a ‘raggedy’  appearance. I presume its original common name was “ragged weed”, only later was the name modified to “rag weed”.  The stems are hairy and may turn pink later in the season. The plants terminate in a green granular spike of tiny green flowers.  Staminate (male) flowers form on the upper part of the spike. These appear as down-turned, green “cups” which form the copious yellow pollen in the late summer or early fall. Any disturbance to the plant at these times generates the release of a cloud of yellow dust (pollen) which drifts off in each current of air.  Ragweed attracts no bees or butterflies—it produces so much wind born pollen that it assures itself and the  species of more than adequate pollination.  This is one reason why it is so common in the urban environment—it can grow in low humidity, poor acid soils, and it needs no wild insect pollinators. Each plant which emerges in the spring can produce tens of thousands of tough woody coated tiny seeds by fall. The seeds have no particular dispersal adaptations except their tough coat which permits them to lie dormant and viable in the soil for tens of years. They are so numerous that moving soil, animal burrowing, natural soil movements, and human activities (soil adhering to boots or vehicle tires) disperse them effectively.

 

Ragweed is not nearly as common as the near ubiquitous, invasive and closely related species: Mugwort ( Artemisia vulgaris) which it closely resembles. As noted above, the leaves of Ragweed have a fern like shape while those of Mugwort are aromatic when crushed and of a simple palmate (hand) shape

Ragweed was the first plant species I learned to identify.That may be because it was the most common weed pest in the empty building lots and waste places of Brooklyn, NY in the 1950-60s. Then too, it’s “ragweed” name is so appropriate, it was easy to identify. The leaf shape does make the plant look like a “ragged weed”. 

Another reason is that this plant is one of the few tough enough to grow prolifically in a building-shadowed urban environment. Ragweed seeds often  sprout from cracks in a concrete sidewalk, or an uncared for patch of  barren soil, or just about anyplace where a teaspoon of soil in a mortar gap in a brick wall give their seeds a toe hold to germinate. That is all it needs. 

On my daily walk today, I counted 59 individual plants of Ragweed in a one-meter wide by one-mile long (1.6 Km) grass-border of the Brookhaven Rail Path. This linear area of about 1,600 sq meters is mowed only irregularly.  In this strip, grass species had grown to a height of 8-10 inches.  Other species observed, included Toad Flax (Linaria vulgaris), Queen Anne’s Lace, Bush Clover or Lespedeza, White Sweet Clover, and most commonly, Mugwort (Artemesia sp), and others. The count of  59 plants per 1600 square meters seems unimpressive—but even at low numbers Ragweed has a great impact on its surroundings, due to its impressive pollen and seed production.  (Note: on September 10—I counted 310 Ragweed specimens in a one meter wide, 1.6 Km  strip in a more infrequently mowed area than above. I noted too, that only a few of these more common plants were producing pollen at this date.) 

Many of the Ragweed plants I counted today (Sept 7) had mature staminate flowers. These appear as a sprinkling of tiny gold particles scattered over the green, upright flower spike. Each one I touched released a cloud of yellow pollen. Of the 59 plants I counted today, perhaps one-third, or about 20 were producing pollen.  Botanists claim that each plant may produce as many as a million pollen grains per day.  Each grain is only about 20 micrometers in diameter.  (A micrometer or μm is: one, one-millionth of a meter.  (Imagine the meter stick (about one yard long). It has one thousand subdivisions (or millimeters), each millimeter (mm) is about the thickness of your fingernail. If you divide one millimeter 1000 times, each of these smaller subdivisions is a micrometer (μm).  Think of 20 micrometers as about the diameter of a Ragweed pollen grain. Such tiny grains are so small that they may remain lofted in the air for long periods of time. and thus travel even hundreds of miles from their source. So today September 7, the Ragweed pollen season begins.  

These pollen grains, naturally serve to pollinate other Ragweed plants. But the enormous number of ragweed pollen grains also affect other species too. The tiny grains can act as air-borne allergens.  When humans  come in contact with this pollen—they may respond with an allergic reaction—such as: runny nose, tearing eyes, cough, even skin reactions such as hives and rashes. About 23 million Americans are said to be allergic to Ragweed pollen.  Those who are allergic may also react to certain common foods. In particular, those closely related to  Ragweed, may generate an allergic reaction.  Ragweed is a member of the Asteraceae Family (i.e. Aster, or Daisy family). So chamomile, sunflower seeds, artichokes, may trigger an oral or systemic reaction as a result of what is termed an “oral allergy syndrome”.  (Some claim other fruits or vegetables not closely related, such as mangos or cucumbers may induce a response as well, but I suspect these may arrive in you kitchen simply contaminated with ragweed pollen),

Pollen  season begins in late August or early September and lasts into November.  Unlike certain tree pollen allergies, such as oak pollen in the north and certain pine pollen in southern states, Ragweed is ubiquitous—and is found in every state in the Union. (Although in Alaska, and Hawaii, Ragweed is found but is not very common, and thus are havens for Ragweed sufferers.)