Every year, thousands of people suffer from allergies, a condition known as seasonal allergic rhinitis. Most allergy sufferers attribute their discomfort to plant pollen of all types and have pursued governmental regulation of plants, mostly ornamental specimens, thought to cause allergic reactions. The truth of the matter is, not all pollen causes these seasonal reactions, and there is no steadfast rule as to what types of plants are producers of allergens. Sometimes, it's not the obvious plant causing the allergic reaction. For example, when ragweed pollen is disbursed, many people have a reaction, but since they don't see the tiny flowers on the ragweed, they assume it's the pollen from the larger flowered goldenrod which blooms at the same time.
Allergy suffers have waged a war against the plants considered to cause the greatest problem -- those that are wind pollinated and produce huge amounts of small, very fine pollen. Unfortunately, this is not always the case, since plants like pines and true cedars depend on wind for pollination and produce great amounts of waxy-coated pollen, but they do not stimulate a reaction. Plants with colorful or fragrant flowers, usually insect pollinated, are considered "safe," non-allergenic plants because they produce their large, heavy pollen grains in relatively small amounts. The pollen are covered with a sticky substance and are not usually carried by wind. Some insect-pollinated plants do, however, produce pollen in amounts large enough to cause allergic reactions, such as Russian Olives and Willows.
Plant pollens are not the only allergens causing severe reactions. Many molds and mildews are a large source of spores that affect people all year round. Other factors, such as air pollution and dry windy conditions, accentuate allergic reactions. The individual's environment also influences hypersensitivity to allergens (substances causing a reaction) -- the greater the exposure, the greater incidence and degree of illness.
To avoid acute allergy problems in the home landscape, several steps can be taken. Individuals suffering from allergies can make informed decisions about plant materials least likely to cause attack, choosing "safe" plants that have large or sticky pollen grains not likely to be transported by wind and female cultivars which do not produce pollen at all. Keeping grasses mowed to appropriate heights decreases their pollen production. Weeds, molds, and mildews should also be controlled. If there is an existing pollen problem in your landscape, replace that plant with a less allergenic selection.
Diane Relf, Extension Specialist, Environmental Horticulture
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