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In search of the giant ragweed
By Forrest Mims III - Express-News : September 12, 2010
One of the worst enemies of fall allergy sufferers is ragweed pollen.
Because its pollen is so efficient in triggering severe cases of hay fever, Delena Tull described the giant ragweed as “the most despised weed in America” in “Edible and Useful Plants of Texas and the Southwest” (University of Texas Press, 1983, pp. 45-47).
The appearance of ragweed pollen grains lives up to their reputation. Through a microscope, the grains resemble soccer balls coated with an array of spikes.
Many reports on the Web claim that a single ragweed plant produces a billion pollen grains. But that number is much too small.
While trying to find the source for the claim, I found a report by William Gratera and Thomas Stemena that claimed a single ragweed plant can release eight billion pollen grains in only five hours!
Those pollen grains are not transferred between plants by bees and other insects. They are spread by the wind.
There are some 40 species of ragweed, among them the common ragweed and the giant ragweed that infest South-Central Texas. This year, comparatively few common ragweed are growing from the field where I make sunlight measurements, probably because of a campaign waged against them for the past several years.
Giant ragwweeds are another story, and this year our place has produced a bumper crop of these monster plants.
Giant ragweed pollen is considered one of the most noxious by allergy sufferers. That's bad, because the pollen-releasing flowers grow near or at the very top of the plants. Typical giant ragweeds in South Texas are from eight to a dozen feet tall, which means the pollen can be blown a greater distance than that from common ragweeds much closer to the ground.
While most references I checked claimed that giant ragweeds reach a dozen feet, a few claimed 16 or even 17 feet. These numbers needed to be verified, so I visited some of our ragweed groves, slipped through the trunks of the giant plants, clipped off four of the tallest ones and dragged them into the sunlight.
Back at the house, my daughter Sarah helped me measure the height of these plants. One from near the Geronimo Creek measured 161/2 feet. Two from near our house were nearly 19 feet tall. The record was truly a giant ragweed, a monster that measured 21 feet, 1/2 inch.
While this is four feet taller than the tallest ragweed I have found on the web, records are made to be broken. So, fellow Texans, can you break this record?