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Allergy Basics

Allergic Rhinitis: Weed Pollen

Summer is half over by the time grass pollens are finished doing their job. That's when weed pollens, which have waited patiently, spring forth. Those pesky plants that, along with cockroaches, will inherit the earth someday are ready to take over pollen production from midsummer to mid-fall. This section looks at the ways that weed pollens can cause allergy havoc for millions of Americans.

Ragweed Is King

When it comes to weed allergies, ragweed is the star. Its pollen is one of the most potent. Only a few ragweed pollen grains are needed to produce hay fever, which is bad news considering that one ragweed plant can produce one billion pollen grains in a season. This demon plant knows no boundaries and in some places can grow 12 feet or higher. Ragweed pollens love to book one-way tickets out of town: Ragweed pollen has been found 400 miles out to sea and two miles up in space.


While there are few places to hide, ragweed isn't fond of areas in upper New England or the southern tip of Florida. The West Coast has western ragweed, which is not as bad as giant ragweed but still causes allergies. While the Rocky Mountain states don't have ragweed, they do have other weed pollens.

Other Types of Weeds

Some weeds are prolific pollinators. Take dock weed for example, which comes in several varieties -- bitter, green, white, and yellow; it pollinates from April all the way to December.

Other weeds to watch out for include aster, cattail, clover, dandelion, fireweed, mugwort, nettle, pigweed, California poppy, rabbit brush, sagebrush, and Russian thistle. Along with the nuisance weeds, some crop weeds, such as alfalfa, hemp, hops, sweet clover, and sunflower, produce pollens, too.

Monitoring Weed Pollen

Allergists and meteorologists help you stay on top of pollen allergies by constantly assessing and reporting on the amount of pollen in the atmosphere. During pollen season, these experts take daily pollen counts, which measure the number of pollen grains in one cubic meter of air during a 24-hour period. Pollen is collected with a plastic rod or similar object that is covered in a greasy, sticky substance. The rod rotates or spins continuously, collecting pollen specimens that are then examined under a microscope and counted. Local wind currents, rainfall, and humidity sometimes limit the accuracy of the readings.

Many newspapers list local pollen counts on the weather page and some newscasts announce pollen counts during the weather report. Always remember that the pollen count you hear on the news is 24 to 48 hours old and counts can change quickly depending on weather conditions. Pollen counts are worse on clear, windy days and generally improve on rainy days or after the first light frost. Make note of the weather conditions the day prior (when the pollen count was taken) before drawing any conclusions about present-day pollen conditions.

Where to Find Pollen Counts

If you don't see the pollen count in the paper or on television, you can get pollen counts by going to the following site(s) on the Internet:

Now that we've covered grass and weed pollens, it's time to take a look at two more causes of allergic rhinitis. The next section will cover the evils of mold spores and house dust mites.

This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.