Ragweed spreads and has tiny flowers on stalks and fern-like leaves.
Photo: Kevin McKeon
Ragweed, Not Goldenrod, Is the Reason You’re Sneezin’
By Kevin McKeon, Maine Master Naturalist
From summer until a heavy frost, watery and itchy eyes, along with sneezing and runny noses, fill the lives of folks with hay fever; for those with underlying conditions like asthma, it’s even worse. Many things can cause these unpleasant conditions throughout the year, so allergy season and its causes are generally defined to be three separate times: Early Spring, from tree pollen; summer, from grasses and ragweed; and autumn, from mold and ragweed. So, ragweed is the primary allergen from mid-summer until the first killing frost, which usually isn’t until October. It produces copious amounts of very lightweight pollen that’s easily wind-dispersed throughout vast areas. Its pollen has been found 400 miles from its source and up to two miles up in the air! And it does this for 1½ to 2½ months. So susceptible folks find it difficult to escape its effects for any length of time.
Climate change has exacerbated this. The increase in CO2 atmospheric levels has provided plants with more food for photosynthesis, making them healthier in many ways, including larger plant size, higher and healthier pollen production, increased levels of pollen toxicity and irritability, and longer allergy seasons due to longer and warmer growing seasons. These factors can both worsen symptoms and affect more people.
So what is it about ragweed that makes it such a noted allergen? And what is an allergen? Our immune systems help protect us from bad stuff like germs by using antibodies to attack them. Sometimes immune systems think something’s harmful when it isn’t. This overreaction, or hypersensitivity, causes the release of histamines, which in turn cause the symptoms of hay fever. An estimated 20% of the U.S. population is affected by ragweed to some extent, and 75% of pollen-allergic folks have ragweed sensitivity. While most allergies can’t be cured, treatments offer relief. Highly susceptible folks and asthmatics are advised to stay indoors and close windows. Or, if you’ve ever wanted to go to Alaska, here’s your excuse: It’s our only ragweed-free state.
There are 17 species of ragweed found in North America, but the only one in Maine is the common ragweed, or Ambrosia artemisiifolia. Ambrosia here means “food or drink of immortality.” It grows up to 3 feet high from seeds the plant produced the previous year; its small green flowers give it an appearance of not being a flowering plant, but those flowers can produce an excess of a billion pollen grains per plant.
A plant can produce up to 60,000 seeds, which can remain viable in the soil for 30 years. They’re rich in protein and fats and remain on the plants through winter, making them a reliable food source for foraging wildlife during leaner times. Rabbits and voles browse on ragweed leaves in the late summer and fall. Goldfinches, sparrows, quail, pheasants, and other overwintering critters find ragweed seeds a valuable winter food source. And these critters become available to feed others in the sparse winter food chain. Deer also visit ragweed, and young game birds and many insects find it a suitable habitat.
There is an unfortunate and widespread misconception that goldenrod causes hay fever, probably because many goldenrods bloom during hay fever season. However, its pollen is too heavy to be wind-carried, relying instead on animal pollination. Its nectar also feeds many bee, butterfly, and bird species. Both ragweed and goldenrod are pioneer species that tend to populate disturbed and eroded areas — like roadsides, ditches, fire-damaged and newly-timbered areas — often forming shared colonies.
And since ragweed relies on wind instead of critters for pollination, its flowers have evolved to be inconspicuous to wildlife; and these flowers are often mistaken for pre-blooming goldenrod buds, adding to the confusion. But a key difference is easily seen in the leaves: Ragweed leaves are fern-like, while goldenrod’s taper to a point at both ends.
So, most of us can rest easy while immersing ourselves in a goldenrod meadow, realizing that its pollen has a difficult task to reach our nostrils, and that these golden beauties feed a host of wildlife during late mid-summer to late autumn season. And even the despised-by-many ragweed has its place in nature’s landscapes.
Editor’s note: Did you see something unusual last time you were out in the woods? Were you puzzled or surprised by something you saw? Ask our “Out in the Woods” columnist Kevin McKeon. He’ll be happy to investigate and try to answer your questions. Email him directly at: kpm@metrocast.net
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