Extension Educator, Horticulture
A snort, a sneeze, followed by two sniffles. Ahh it's the call of the allergy sufferer. With the tell-tale symptoms of sneezing, runny nose and itchy watery eyes an estimated 50 million people suffer each year from allergies. Although people can be allergic to many different things (pet dander, work, mold, and fragrances), pollen is a common allergen.
As fall approaches goldenrod shows off its bright yellow flowers so most people blame it for their summer allergies. In reality the disregarded ragweed is the likely culprit. Goldenrod pollen is not physically adapted to be an allergen. It has showy yellow flowers to attract its insect pollinators. Its pollen is heavy and sticky so it will cling to the insects for a ride to the next flower. Heavy sticky pollen does not blow well in the wind or up your nose. However ragweed has homely tiny green flowers and relies on wind pollination. Ragweed overwhelms the air with lightweight pollen in the hopes it will land on another ragweed flower. Each ragweed plant can produce an estimated one billion pollen grains. Just a few plants can create an invisible cloud of polluting pollen.
In our area two ragweed species are the most abundant: common ragweed (Ambrosia artemisiifolia) and giant ragweed (Ambrosia trifida). Both are native annuals that reproduce from seeds. Common ragweed is indeed common along roadsides, cultivated fields, vacant lots and pastures. It grows one to four feet tall with densely hairy stems and deeply lobed (almost ferny) leaves. Common ragweed grows well in gravelly areas along roads where it thrives under abuses that would knock out most plants.
Giant ragweed is a larger version at 13 to 15 feet tall. Its coarse, rough stems hold large, slightly hairy leaves that grow almost a foot long with three or sometimes five pointed lobes. Giant ragweed can be common in cultivated fields, fence rows, roadsides and unmown construction sites. Some populations of giant ragweed survive even after herbicide applications.
Ragweeds are very competitive plants that succeed in areas where few other plants will live. As first invader plants they love disturbed soil. People are very adept at disturbing the soil through tilling and construction. Ragweed seeds can survive in the soil for over thirty years, just waiting for proper conditions for germination.
We are hard pressed to find a good use for ragweed; however the fruits are a highly nutritional food for songbirds and other wildlife. Prehistoric Native Americans reportedly collected the fruits for food and may have actually cultivated giant ragweed.
Since ragweeds are annuals their control hinges on eliminating seed production. Plants are starting to produce seed right now so hoeing and cultivating can help to reduce their populations. Next season remove plants in May before they flower.
Since ragweed pollen is a common allergen doing your part to control them helps everyone. People's sensitivity to certain plants can vary widely so always discuss your allergies with your health care professional. Plants shed pollen at different times of the year so a look at the calendar might help to narrow down the culprit.
Gardening during allergy season can be a challenge. Weather conditions can make a difference in the pollen levels. The most favorable conditions for high pollen are warm and dry while high humidity and rainfall lessens pollen release. Also the time of day can influence pollen levels. Pollen release is highest in mid-morning after dew has dried.
If you do go outside during the worst times for pollen levels, reduce your exposure by wearing gloves, a long sleeved shirt, hat and sunglasses or goggles. A pollen mask may be necessary. After working outside take a shower and thoroughly wash hair and clothes. Look forward to October. Ragweed allergy season generally lasts through September.