What is Ragweed?

Ragweed is a plant that grows for one season and then it dies.

It is unique in that you can see female flowers and male flowers growing close to each other on the same plant.

The male flowers are found higher on the plant and the female flowers grow below the male flowers.

In the pictures below, the spikes are the male flowers and the female flowers are the leafy parts under the spikes.

The Pollen

The male flower produces much more pollen then the female flowers need. This type of plant depends on wind pollination. There are very few insects that are attracted to this plant.

This over-production of pollen insures the survival of the plant.

• With so much pollen being produced, the plant will cross-pollinate. This causes a lot of variation. It causes diversity in the genetics which makes it harder for herbicides to continue to be effective.
• As an annual, the plant may die at the end of the season but the seeds remain viable. The seed can remain dormant for years in the soil and then start to grow when the conditions are right.
• The shear number of pollen production insures the survival of the plant. One plant is capable of producing a billion pollen grains in one season. To put this in perspective, corn may only produce 4 million pollen grains in a season.

Facts

• 41 species world-wide
• 21 species in North America
• A prolific producer of pollen
• Considered the King of Pollen Allergy
• Contributes to allergic asthma and allergic conjunctivitis
• Grows in bean and corn fields and responsible for reducing the yields of those crops

Pollen Season

The end of summer to frost is the time of year that the plant produces pollen. Exactly what time on the calendar that pollen production begins depends on the geographic location. Generally speaking, the farther north you travel, the later the production begins.

Once the pollen production has begun, ragweed season does not stop until the first frost kills the plant. The pollen is so lightweight that the wind can carry it for hundreds of miles.

Ragweed Allergy

The plant relies on the wind to carry its pollen. Pollen is a protein that carries the male parts of the flower to the female part in plant fertilization. When people get in the way of this process, the protein in the pollen produces allergy symptoms in those who are sensitive to it. The majority of people who are allergic to some type of pollen are also allergic to ragweed.

The pollen is a very potent allergen. It does not take much of the protein to trigger an allergic reaction. The shear number, coupled with the amount of time that the pollen stays airborne, makes it impossible to avoid. It is the number one cause of pollen allergy.

Growing Conditions

This type of weed is a very competitive. It is extremely aggressive. It can compete with all the tall vegetation around it. It can be easily found in places such as

• Vacant lots
• Riverbanks
• Along the roadside and in the ditches along the roads in the country
• Vacant fields construction sites
• Along lakes and streams
• Farmland
• Sunny, grassy plains
• Sandy soil
• Abandoned fields
• Anywhere that the soil is disturbed or bare

Where the soil is disturbed is the ideal growing conditions. Often, these conditions are found in construction sites. To build a large commercial building, a lot of excavating and dirt moving takes place. It is not uncommon to see mounds of dirt made during this process. As the pictures below shows, this makes for an ideal environment for the seeds lying in the dirt dormant to come alive.

Along the road is another great place for this weed to find a home. The Department of Transportation keeps vegetation next to the road at a minimum. As a result, the bare soil gives the perfect condition for the seed to germinate. As you can see from the pictures below, short ragweed is found next to the asphalt because it can survive being mowed by the D.O.T.

Types of Species

There are many different kinds of species causing ragweed allergy. The two that are talked about the most is short and tall species. This is because it is those two kinds that cause allergy sufferers the most problems.

Short Ragweed
This type is known as Ambrosia aratemisiifolia, better known as common ragweed. It is found in more locations than any other type. You can even find this growing in your own yard. It can grow up to 4 feet tall, depending on the conditions.

The leaves of this species have a carrot-like or fern-like quality. The leaves grow opposite of each other and can be as long as 6 inches on the larger plants. The tips are rounded and the leaf is deeply lobed.

Giant Ragweed
This type is known as Ambrosia trifida, better known as Great Ragweed (or Horseweed). It may not be found as common as the short species, however, it is the best pollen producer. The pollen is potent but not quite as strong as the shorter one. It can grow 5-6 feet tall and can reach 14-16 feet in ideal conditions.

With the height of this plant, it can be very competitive to all the row crops that farmers plant. The crop rotation and tillage by the farmer helps the plant get established. As a fast grower and one that starts early, this species has the advantage.

The leaves are big and have 3 or 5 lobes. They can grow to be 12" long and as wide as 8 inches.

Summary

Ragweed causes my family more allergy symptoms than any other type of allergic rhinitis. There are 2 main species of prolific pollen producers. Both types are very common. Now that I have shown my family what the plant looks like, they comment on how they now see it growing EVERYWHERE! When you're allergic to this plant and it is pollen season, knowing what it looks like makes it stand out from the other weeds.

Go to the nasal allergy HOME PAGE.

Related Topics

Fall Allergies: See pictures of ragweed developing.

Back to Top