Extension News

Goldenrod Falsely Accused

Blooming goldenrod plant

Note to media editors: This is the Garden Column for the week of Aug. 17, 2007.

8/13/2007

By Linda Naeve
Program Specialist
Iowa State University Extension

Occasionally we hear or read about a person who was wrongly accused of a crime. When all the facts are analyzed and evaluated, they prove that someone else was responsible. Unfortunately, the reputation of the innocent individual is questioned for a long time after being cleared.

That same scenario plays out in the plant world. That is, one plant may be acquitted of the crime, but is still getting the blame. It occurs in early and late summer when hay fever sufferers blame certain plants for their misery.

Hay fever is an allergic reaction in certain people when they inhale pollen from specific plants. Although the pollen of several plants, such as trees, grasses and weeds, can cause allergic reactions, the plant species at fault and the symptoms are very unique and specific to individuals.

Before we start blaming specific plants for our runny noses, we need to get the facts straight and then narrow down our list of suspects. Pollen is barely visible, yet it varies considerably in size, depending on a plant’s mode of pollination. Insect-pollinated plants produce large, sticky pollen grains that pose no risk to hay fever sufferers because even in windy weather it is too large to remain airborne. It is designed to stick to the bodies of visiting insects. The very tiny, light pollen of wind-pollinated plants are the predominant culprits. Their pollen can soar and remain in the air for a long time. Fact #1: Most trees and grasses and some weeds are wind-pollinated.

When determining what plants are to blame, consider the time of year when hay fever symptoms appear and are the worst, then look to see what is in bloom in your area. Fact #2: Several weeds and grasses are blooming at this time. A quick glance in the ditches and gardens narrows the list of suspects.

One of the most colorful plants we see blooming in roadside ditches and gardens in late summer is goldenrod (Solidago sp.). Hay fever symptoms seem to be worse when it is in bloom so it often accused of causing hay fever. One look at goldenrod and a little logical thinking clearly eliminates it as a suspect. The many, small, bright yellow flowers on long cluster on the top of the plants are often covered with butterflies and bees taking advantage of the abundance of nectar. The brightly colored flowers are important to attract color-sensitive insects required for pollination. Fact #3: Goldenrod is insect-pollinated. The pollen grains are relatively large, heavier than air and intended to be carried off by bees, butterflies and other pollinators.

On the other hand, the tiny green flowers on ragweed make large amounts of tiny pollen that is carried from one plant to another by the wind. Research has shown that ragweed pollen can travel far. It has been measured in the air 400 miles out to sea and 2 miles up in the atmosphere, but most of it falls much closer to its source. Fact #4: Ragweed produces lots of airborne pollen making it is easy for people to inhale the tiny pollen grains.

Goldenrod can grow nearly anywhere, but is often found growing on the edges of woodlands and in sunny ditches and weedy areas where the soil has been disturbed. This is also the same habitat where common and giant ragweed thrives. However, since ragweeds are rather inconspicuous plants without showy flowers they are overlooked or ignored. They don’t have colorful, nectar-filled flowers because they don’t need to attract pollinators.  Fact #5: Ragweed and goldenrod bloom at the same time and in close proximity.

So, after examining all these facts, it is clear to see that goldenrod is not the cause of hay fever -- it is guilty only by association. The real culprit is ragweed.  It probably causes more grief to hay fever sufferers than any other plant in the fall. Of all Americans who are allergic to pollen-producing plants, 75 percent are allergic to ragweed.

Fortunately, many people are now aware of goldenrod’s innocence and have recognized its beauty and value. It is native to most of the United States and plant breeders have developed many varieties that are perfect for perennial gardens throughout the country. Goldenrod has even been adopted as the state flower of Nebraska and Kentucky.

Photo caption: Several species of Goldenrod (Solidago) are native to the United States. This beautiful fall-bloomer is not a source of hay fever.

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Contacts :

Linda Naeve, Horticulture, (515) 294-8946, lnaeve@iastate.edu

Jean McGuire, Extension Communications and Marketing, (515) 294-7033, jmcguire@iastate.edu

There is one photo for this week's column.

Goldenrod8-17-07.JPG