But ragweed sufferers take note: according to François Tardif, an associate professor at the University of Guelph, the new strain won’t have much of an impact on your allergies. “There is so much ragweed out there that the pollen from resistant plants is like a drop in the ocean.”

Rather, farmers are the ones who will suffer the most. This new strain is so resistant that it can easily take over farmers’ fields, wreaking havoc on the harvesting of crops.

Although other herbicides can be used, they are not as effective as glyphosate. Soybean crops are most affected by glysophate-resistant ragweed, which can have a significant impact in the food industry because, as any soy-allergic individual knows: soy and its derivative soy lecithin are found in many packaged foods.

The ragweed in my backyard in the Ottawa Valley waves at me smugly every morning. It has formed a towering wall along the back corner of the small meadow we’ve let flourish as an environmental gesture. All the other wildflowers in the meadow co-exist happily, but the ragweed, which characteristically found a toehold in the least promising soil, has now started to elbow its way toward to the front. Unfortunately, its braggadocio is well-founded.

Not only is ragweed an aggressive competitor, it is an able procreator that produces pollen of unrivaled allergic potency. Its pollen triggers reactions in up to 75 per cent of hay fever sufferers, depending on where they live in North America, making this one weed to be reckoned with.

Operation Proliferate

The tens of millions of Americans who now suffer from ragweed allergies can thank Canada for their misery. Common ragweed’s likely point of origin in North America was Ontario, according to Dr. Peter Creticos, clinical director of the Division of Allergy and Clinical Immunology at Johns Hopkins School of Medicine in Baltimore. He jokingly calls ragweed “Canada’s gift to the colonies,” referring to the plant’s ability to dump hundreds of thousand of tons of dust-like pollen across up to 1,000 kilometres of the continent every year.

Now ragweed can be found all across eastern and central Canada and the United States, though there is thankfully little of it west of the Rockies. The crown-shaped seeds are highly mobile and have even deployed overseas, particularly near existing and former Canadian and U.S. military bases in Western Europe.

Creticos suspects the seeds hitched a ride on equipment shipped from North America during and after the wars, then launched a horticultural offensive into Eastern Europe, where it now enjoys a strong presence. For allergy sufferers, misery loves company.

Flourishing on the Farm

Back in North America, common ragweed and its big brother, giant ragweed, are causing havoc in the crop farming sector. Clarence Swanton, a University of Guelph professor and weed scientist, says ragweed grows well along roadsides and train tracks, but really loves the rich, loosely tilled soil of corn, soybean and cereal crop fields.

“Ragweed seedlings emerge early and therefore are very competitive with the crop for light, water and nutrients,” he says. Swanton estimates bean crop losses in Ontario alone range from 8 to 30 per cent, representing millions of dollars annually.

The Ontario government’s chief of weed control, Mike Cowbrough, says uncontrolled ragweed can cause yield losses of up to 80 per cent in some operations – a financial disaster for farmers. He says ragweed is one of the toughest weeds to control: it takes repeated mowings to prevent the plant from blossoming, its seeds can remain dormant for up to 50 years, and several strains have become resistant to traditional herbicides.

In the United States especially, some ragweed has even become immune to glyphosate (known in the retail sector as Roundup), once thought to be the magic bullet for weed control.

Frustrated farmers with glyphosate-resistant ragweed are creating herbicidal blends, incorporating older herbicides like 2,4-D and dicamba in hopes that their ragweed is not resistant to those mixtures. But farmers who market organic produce are in a conundrum, since herbicides are a no-no. Control often has to be done mechanically with a cultivator, which can speed soil erosion, or even manually.

Soybean farmers must also contend with ragweed’s staining quality, which can turn the pristine white soybean – and the tofu it’s used to make – to an unappealing shade of green.

Next Page: The Problem Grows

Allergic Signs
Symptoms of an allergy to ragweed range from mild irritation of the eyes and a runny nose to completely congested sinuses; itchy eyes, mouth and throat; and sleeping problems, accompanied by fatigue and irritability.

Ragweed can provoke asthma. It is also linked to ear infections in children and sinusitis (bacterial infection of the sinuses) in adults. However, skin reactions to ragweed are rare.

The Where of It
Though there are dozens of varieties of ragweed, two are mainly responsible for the sneezing and weeping of allergic rhinitis: common ragweed (Ambrosia artemisiifolia) and giant ragweed (Ambrosia trifida).

In the United States, ragweed cuts a swath through central and eastern states from north to south. In Canada, Ontario is the hardest hit by its pollen, with Manitoba and Quebec following closely behind. In both countries, the coasts are mainly clear of it.

Weather’s Effect
Ragweed thrives during dry, hot summer weather. While most of us complain about clammy and rainy days, high humidity (over 70 per cent) makes it more difficult for the plant to release pollen.

Know the Enemy
Common Ragweed: An annual, it grows erect and as tall as 5 feet (150 cm). Lower leaf branches are opposite each other, but begin to alternate higher up the plant. The leaves are long and compound, with deeply toothed divisions on each leaf. Flowers are in spikes of small, greenish yellow florets, numerous and not showy.

Giant Ragweed: The weed lives up to its name, reaching as high as 15 feet (4.5 m). Its stems are multi-branched and hairy, with the leaves opposite, except on smaller branches.

The leaves are large, as rough as sandpaper, rounded and shallowly toothed. Flower heads are similar to common ragweed except the female head is larger. This is an annual as well, and both plants only reproduce by seed.

The Pollen: Flowers begin appearing in June, but don’t release pollen until the tail end of July, with pollen saturating the air from August through October. One plant will produce one billion pollen grains per season. Only the first frost will kill ragweed.

Next: How to Beat the Weed!