How to get rid of ragweed in a pasture?

Reducing Ragweed in Pastures

Both common ragweed, which is an annual, and western ragweed, which is a perennial, can be held in check using similar methods. However, common ragweed is controlled more easily with grazing management or herbicides than western ragweed.

Research and observations both show that ragweed problems are worse in pastures that fail to maintain competition from a full leaf canopy of grass during late May through late June. If you had ragweed problems the past couple of years, look for tiny plants or seedlings underneath your grass during the next few weeks. Heavy grazing or haying during this time opens up the grass sward, letting these seedlings and small plants grow rapidly.

Any management that develops and maintains a dense leaf canopy will help reduce ragweed problems. This includes increasing grass growth with fertilizer and thickening stands by seeding. Most importantly, avoid grazing heavily in areas with ragweed problems. If you do graze heavily or cut hay, spraying herbicides like 2,4-D or Grazon or Curtail or Weedmaster after grazing or cutting gives good control of ragweed seedlings and small plants. And if ragweed gets away, shredding in September can reduce seed production.

It takes time, and a well-planned approach, to control ragweed in pastures. With good grazing, some spraying, and timely shredding it can be done.

Controlling Weeds in Late Summer

Weed populations have exploded recently in many pastures. Plants like ragweed, ironweed, goldenrod, and vervain have become a common sight. Many pastures were drought stressed last year and recent summer rains have stimulated a late season revival of these weeds.

What do you do about weeds at this time of year? Applying herbicides for weed control does very little good on mostly mature weeds this time of year. Spraying may reduce some seed production if applied early enough and should make pastures look nicer, but overall, herbicide applications at this time are not an economically sound investment. Mowing would probably be a more attractive alternative to limit seed production in these species.

Long-term weed control in your pastures is certainly a better financial investment. Good grazing management next year that leaves some residual grass cover can go a long ways towards minimizing the competitiveness of many of these weed species. Improving the health, vigor, and density of your grass stand makes it more difficult for these weeds to get started in your pastures.

Timing herbicides applications for when weeds are most susceptible is critical to making the most economical use of these products. Spraying in early-June is generally when chemicals will be most effective, especially with herbicides like 2,4-D, Grazon, Banvel, or Curtail.

But don’t put the sprayer away for the winter just yet. Fall is one of the best times of the year to use herbicides to control both musk and Canada thistle. If you weren’t able to get out and control them this spring, you still have another chance.

With recent rains, Musk thistle seedlings have probably sprouted into a small, in a flat rosette and the rhizomatous Canada thistle has sent up new tillers. This new growth is very susceptible to herbicides at this time of year.

Using 2,4-D or Ally are probably your best bet for the money. However, as it gets colder, a little Banvel mixed with 2,4-D will result in a better kill on musk thistle or use curtail before the soil freezes.

If it gets late and you are not sure how effective herbicides will be, use Tordon 22K instead because Tordon has a lengthy soil residual that will continue to work next spring.

Read more Range Science 101 articles from Eric Mousel

For the past couple of years, ragweed growth has exploded in pastures. This has happened because of the timely spring rains that encouraged germination and seedling growth followed by sunny dry falls that helped seed development.

There are two types of ragweed; the common ragweed, which is an annual, and the western ragweed, which is a perennial. Common ragweed can be controlled with grazing management or herbicides, while western ragweed can not.

Research has shown that ragweed becomes a problem in pastures that fail to maintain grass competition with a full leaf canopy from late May to late June. If you have had ragweed problems in the past, look for small plants or seedlings underneath your grass. By grazing heavily or haying during this time, you will open up the grass sward, letting small plants and seedling grow rapidly.

By developing a grazing management that maintains a dense canopy at this time will help reduce ragweed problems. This can also be done by increasing grass growth by adding fertilizer or thickening strands by seeding. The most important part is to avoid heavy grazing where ragweed is a problem. If you cut hay or have grazed these areas heavily, use one quart of 2,4-D or Grazon after haying or grazing to help control the ragweed seedlings and small plants. Another management strategy is to shred in September to help reduce seed production.

In order to control ragweed, a good management strategy is needed. With timely shredding, some spraying, and good grazing practices, ragweed can be controlled.

Tips For Controlling Ragweed Plants

For an allergy sufferer, having your lawn or garden invaded by ragweed can be near torture. The ragweed plant (Ambrosia artemisiifolia) is a common weed in yards and is one of the worst for pollen production. Controlling ragweed will not only help to keep your garden looking nice, it will also help alleviate the allergy symptoms for people in and around your garden.

What Does Ragweed Look Like?

Ragweed identification is easy due to the distinct leaves and flowers on the plant. Ragweed is an upright growing plant that has leaves that look almost fern-like, feathery and green. You will also notice that ragweed leaves look hairy.

The flowers on the plant are also useful for ragweed identification. The flowers on ragweed are yellow and long, like streamers. There will normally be several clustered flowers at the top of the plant, which look like a fountain, and also several flowers closer to the bottom. The flowers at the top are the male flowers (which produce the pollen) and the flowers closer to the bottom are the female flowers.

How to Control Ragweed

Ragweed plants like to grow in heavy, untilled soil and are frequently found in soil that is uncrowded and has poor fertility. They also do not tolerate being mowed very well. Because of this, one of the best ways to control ragweed in your lawn and flower beds is to make sure that lawns are mowed regularly and open beds are cultivated or hoed on a regular basis.

Also, improving soil by adding compost and other organic materials will not only keep the soil from getting heavy, but will also add nutrients to keep the soil healthy. Both of these benefits will help to keep ragweed from establishing in your garden.

If ragweed plants have already started growing in your yard, you have several methods for getting rid of them.

Herbicides are a common way how to kill ragweed. Ragweed is considered a broadleaf weed, so you can use broadleaf weed killers on it to help get rid of it. In recent years, however, some varieties of ragweed have started to build up a resistance to these common weed killers, so using herbicides may not be 100% effective.

If you decide to use herbicides to kill ragweed, the best time to apply them is mid-spring to early summer. Controlling ragweed at this time will make sure that you are applying the herbicide when the leaves of the plant are still rather immature and tender and, therefore, more susceptible to herbicides.

Hand pulling can be used as an organic way to control ragweed. In a home garden setting, this is the easiest way for controlling ragweed, as the plants are easy to pull and easy to spot. Make sure to pull these weeds out of your garden before they flower. A ragweed plant can produce more than 60,000 seeds if allowed to fully mature.

Note: Chemical control should only be used as a last resort, as organic approaches are safer and much more environmentally friendly.


Common name(s): Ragweed, common ragweed

Scientific name: Ambrosia artemisiifolia

Family: Sunflower or Aster family (Asteraceae)

Reasons for concern: This plant has allelopathic (toxic) properties that inhibit the growth and development of neighboring plants, leading to a monoculture. It produces a huge amount of pollen in the fall, afflicting millions of people who have allergies.

Classification: Native

Special Note: Native plants have evolved together over centuries with pollinators, birds, wildlife and other native plants. We may not understand the role this native plant plays in our environment, so we may not want to completely eliminate it.

Botanical Description: Erect, branching, broadleaf herbaceous plant.

Leaves: Finely divided. Up to 6 inches long and 4 inches across. Young leaves blue-green and hairy. Mature leaves hairless.

Stem(s): Erect. Many branched. Greatly varied in size, up to 3 to 4 feet tall. Green to light pinkish red. Sometimes blue-green. Upper stems end in one or more spikes of flowers.

Flowers: Numerous, small, inconspicuous flowers, initially green. Later turn yellowish-green or brown as they go to seed. Male flowers produce fine, wind-carried pollen, spread in late summer or early fall. There are male and female flowers in clusters on ends of branches, with male flowers found above female flowers. Gravity aids fertilization. Flowering occurs in August through September.

Seeds: Numerous. Seeds mature by October.

Roots: Extensive root system. Fibrous.

Native to: United States, except Alaska and Hawaii, Canada and northern Mexico.

Where it grows: In full sun with average to dry conditions from 5,200 to 8,000 elevation. Along ditches, in waste areas, and other disturbed areas, and areas along roadsides and railroads. In gardens and lawns. In many soil types, including high amounts of clay, gravel or sand, and in sterile soil.

Life cycle: Annual

Reproduction: By seed

Weedy characteristics: Ragweed produces numerous seeds, which remain viable for 5 years or much more. These seeds are easily dispersed by wind, water, and birds, burrowing animals, and humans. It is resistant to drought and grows in many soil types and under adverse conditions. It has allelopathic (poisonous) properties that inhibit growth and development of nearby plants. Repeatedly monitor previous infestations for new growth.

Look-alike native plants: There are several different species of native ragweed (Ambrosia spp.) in northern Arizona which look similar to each other. They all share the same weedy characteristics, reasons for concern, and control strategies.

Control strategies: Hand-pull before plants flower or go to seed, release pollen, and spread seeds in late summer. It is easy to pull. Bag any buds, flowers or seeds. Heavy mulches can greatly reduce growth. Mowing is ineffective. Repeatedly monitor previous infestations for new growth. Plant desirable native species to outcompete invasives.

Images: Click on an image to enlarge and see the image citation.

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Today’s featured Weekly Weeder plant is common ragweed, Ambrosia artemisiifolia. In this post, we’ll explain what ragweed is, identify prime ragweed season, share some ragweed pictures, and talk about ragweed allergies and control.

Common ragweed is also known as ragweed, hayfever weed, bitterweed, bloodweed, crownweed, mayweed and bane of allergy sufferers everywhere. Some other common ragweed species include bur ragweed, giant ragweed and western ragweed.

What is Ragweed?

Ragweeds are common weeds that thrive in disturbed soils. Giant ragweeds can get up to 18 feet tall, but common ragweed typically ranges between a few inches and a few feet. It can hide out along the edge of a lawn or driveway, get mowed, and still manage to flower. When it does flower, it releases an amazing amount of pollen, which is the primary culprit in pollen-induced allergies in the United States.

The seeds of this amazing plant can lie dormant in the soil for over 40 years, waiting for the right conditions. Ragweed specimens are showing up that are resistant to glyphosate (Roundup), so standard weed killers won’t knock it out.

Where Does Common Ragweed Grow?

Common ragweed is native to North America, and is found throughout the United States and most of Canada (See USDA map below). (Aren’t we lucky?) It has also spread over much of Europe, where it has become a problematic invasive species.

Ragweed thrives where other plant struggle – wastelands, vacant lots, aged pastures, stubble fields and other disturbed soils. It prefers full sun, disturbed and slightly acidic soil, and can tolerate (and thrive in) drought.

Where drought or poor soil moisture transfer make potassium unavailable, conditions favor ragweed growth.

Common ragweed is an annual, but it produces thousands of seeds that last virtually forever. Up to 32,000 seeds have been recorded on a single plant.

What does Common Ragweed look like? Ragweed Pictures

The individual leaves are fern-like. It looks pretty innocent when it’s small.

Common ragweed stems are fuzzy. The stems are filled, not hollow.

Ragweed plants are in the genus Ambrosia in the Aster family, which means they are related to daises, asters, dandelions, chamomile and many other flowering plants. Unlike their showy cousins, ragweeds have drab green flower spikes.

When is ragweed season?

Ragweed season peaks in fall, typically around mid-September. The pollen development in ragweed species occurs when temperatures drop below 60 and the nights get longer. August through November are the worst months for those affected by ragweed allergies.

Ragweed plants are killed by hard frosts. With some locations having later fall frosts, those areas are also experiencing a longer ragweed season.

Even if you don’t have ragweed growing in your yard, ragweed pollen is small and light. It can travel up to 400 miles on the wind, sometimes triggering ragweed allergy season in areas where the ragweed isn’t in bloom yet.

Ragweed Allergy

Some studies indicate that ragweed produces up to 90% of the allergy causing pollen in the United States.

Ragweed allergy symptoms include:

  • Sneezing
  • Runny nose
  • Nasal congestion
  • Headaches
  • Eye and throat irritation
  • Aggravated asthma symptoms
  • Other cold-like symptoms

If you are one of the folks who suffer from a ragweed allergy, unfortunately there is no cure. There are pharmaceuticals available to help treat ragweed allergy symptoms (some of them made from ragweed). These are often started before ragweed season hits.

In the article “Like Treats Like: Ragweed to Treat Allergies”, they discuss several historical uses of ragweed as an allergy treatment, including one from Matthew Wood’s Earthwise Herbal:

“Wood recommends that the fresh leaves fresh be tinctured 1:2 in 95% alcohol watered down to 70%. He recommends giving only one drop initially to determine sensitivity. If there is no adverse reaction or an improvement in symptoms, five to 10 drops be given every two to three hours.”

As noted above, ragweed is in the same genus as chamomile, so if you suffer from ragweed allergy, it’s best to avoid chamomile tea.

Those who are sensitive to ragweed may also suffer from oral allergy symptoms that make them sensitive to certain foods, including cantaloupe, banana, zucchini, mango, beans, celery, hazelnuts, potatoes and various other foods. Peeling or cooking these foods may help.

Managing Ragweed Allergies

If you are one of the folks who is bothered by ragweed pollen, unfortunately there is no cure. I’ve noticed that when I watch my diet (plenty of fat to keep nasal and lung membranes well lubricated, plenty of live culture foods, less sugar), my allergy symptoms are much milder. For more help, see 15 Home Remedies for Seasonal Allergies and Hay Fever Symptoms.

Ragweed pollen counts tend to be highest in the morning, so plan your outside activities accordingly. Keep windows closed and use a good whole house filter and/or a room air filter in your bedroom for better sleep. Pollen sticks to clothing, pets and line dried laundry, so swap clothes and wash up after exposure. Skip line drying.

There is some good news for folks living in coastal areas – humidity levels above 70% cause ragweed pollen to clump, reducing the amount that goes airborne.

Ragweed Rash

I found out the hard way that direct skin contact with ragweed plants can cause mild contact dermatitis, AKA ragweed rash. About a day and a half after a pulling number of ragweed plants bare handed from the side of the driveway, I woke up with a palm full of small, itchy bumps. DernNet NZ confirms I’m not the only one with this reaction. I put some plantain oil on the ragweed rash and the itching subsided.

Ragweed vs Goldenrod

Because ragweed and goldenrod both bloom in the fall, many people mistakenly blame their ragweed allergy symptoms on goldenrod, because the flowers are more visible. I even saw allergy sites posting photos of goldenrod and calling it ragweed while researching this article.

While it is possible to have a goldenrod allergy, it’s much less common. Goldenrod has larger pollen grains that don’t easily get carried on the wind – or up your nose.

Medicinal Use of Common Ragweed

Judith C. Evans states in her article “History and Medicinal Uses of Ragweed”:

Ragweed’s medicinal properties include: astringent, antiseptic, emetic, emollient, and febrifuge. Early American physicians recognized ragweed’s medicinal uses, and Native Americans valued it as a topical and internal remedy. Healers and herbalists prepare remedies from the roots and leaves. Crush the leaves and apply the juice to soothe insect bites and poison ivy rashes. Native Americans prepared a poultice from crushed leaves to relieve swelling and prevent infection.

Ragweed also provides aid for internal ailments. Herbalists value ragweed root tea as a remedy for nausea, fevers, and menstrual disorders; Native Americans used the root tea as a laxative. For years, Ozark herbalists have treated diarrhea with tea prepared from the leaves. Ragweed pollen is used in homeopathic remedies for treatment of hay fever symptoms.

I would suggest care with internal use of ragweed, especially if you have any type of allergic reaction to the pollen. Next time I get a mosquito bite, I may try the sap to see if it does indeed soothe the itch.

Ragweed as Food and Habitat for Wildlife

Believe it or not, ragweed is useful. It produce seeds that are rich in oil and provide winter food for birds and small mammals. Fairfax County Public schools website states that “Ragweed is a good source of food and cover for wildlife. Eastern Cottontails eat the plants, and insects, such as grasshoppers, eat the leaves. Some animals which eat ragweed seeds include: Meadow Vole, Dark-eyed Junco, Brown-headed Cowbird, Northern Bobwhite, Purple Finch, Mourning Dove, American Goldfinch, and Red-bellied Woodpecker.”

(Side note – the seeds of giant ragweed are edible for humans, too. They have 47% crude protein, more than other cultivated grains, and were once cultivated by Native Americans for food.)

Note: Ragweed gives milk an “off” flavor, so it’s best to limit ragweed growth in pastures. (See below.)

Ragweed Control

In the book “Weeds: Control Without Poisons“, the author notes that ragweeds proliferate where drought and lack of moisture availability in the soil makes potassium unavailable. Hardpan, gravel, compacted soils, crusty soils are all prime ragweed territory. As soil improves, other plants will likely out-compete the ragweed.

In my yard and garden, the usual soil measures (adding compost and organic fertilizers, mulching) have virtually eliminated the ragweed. The primary spots we still see it are around the edge of the driveway, and on compacted, dry soils. For control in fields and pastures, “Weeds: Control Without Poisons” specifies: “Manage ragweed with manganese, copper, , vitamins C and B-12, calcium, phosphate and sugar in a solution. Determine quantities on site according to test readings.” The author also encourages tillage and mowing to knock back the growth.

Why Weeds?

The word “weeds” often has a negative connotation, but I think of them simply as plants not purposefully planted. They are often useful, and fill a spot where something needs to grow. (If you don’t plant, Mother Nature will.)

Our weeds hold the soil in place, plow compacted subsoil, draw up nutrients, provide medicine, feed wildlife (and people) – they are a treasure, not a curse. As you tend your yard and garden and the soil improves, unwanted volunteers will either disappear on their own, or be much easier to manage.

Recommended resources:

  • Wildflowers of Wisconsin
  • Nature’s Garden: A Guide to Identifying, Harvesting, and Preparing Edible Wild Plants
  • The Forager’s Harvest: A Guide to Identifying, Harvesting, and Preparing Edible Wild Plants
  • Backyard Foraging: 65 Familiar Plants You Didn’t Know You Could Eat
  • Edible Wild Plants: Wild Foods From Dirt To Plate

Thanks so much for stopping by to visit. Help stop the overuse of herbicides by spreading the word about putting our weeds to work and sharing this post.

You may also find useful:

  • Top 10 Edible Flowers, Plus Over 60 More Flowers You Can Eat
  • The Weekly Weeder Series
  • My Favorite Wildcrafting Resources

Originally published in 2011, updated in 2017, 2018.

Ministry of Agriculture, Food and Rural Affairs

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Ontario Weeds: Common ragweed

Return to the Ontario Weeds Gallery

Excerpt from Publication 505, Ontario Weeds, Order this publication

Table of Contents

  1. Name
  2. Other Names
  3. Family
  4. General Description
    • Photos and Pictures
  5. Stems and Roots
  6. Flowers and Fruit
  7. Habitat
  8. Similar Species
  9. Caution
  10. Related Links

Name: Common ragweed, Ambrosia artemisiifolia L.,
Other Names: petite herbe à poux, Short ragweed, ambrosie a feuilles d’armoise
Family: Composite or Aster Family (Compositae)
General Description: Annual, reproducing only by seed.

Photos and Pictures

Common ragweed (A – plant beginning to flower; B – spikes of male flower heads ready to release pollen).

Stems & Roots: Stems erect, 15-150cm (6-60in.) high, usually much-branched, hairless or hairy throughout; lower leaves opposite (2 per node) but becoming alternate (1 per node) higher on the plant, bright green to slightly yellowish-green on young plants, becoming grayish-green on older plants, compound and finely divided, the final divisions usually coarsely toothed.
Flowers & Fruit: Flower heads not showy, individually small, 2-5mm (1/12-1/5in.) across, green and inconspicuous but very numerous and forming distinctive inflorescences; individual florets either male or female, but never both; all flowers within one flower head either only male or female, but both male flower heads and female flower heads usually present on the same plant; heads of male (pollen-producing) flowers in raceme-like elongated clusters at ends of branches, each male head hanging downwards on a short stalk like a tiny inverted umbrella; female (seed-producing) flower heads in axils of short, narrow, green bracts near the base of each long cluster of male flower heads, each female head with only a single flower and producing a single, hard, somewhat triangular or diamond-shaped seed with several, short, sharp spines around the upper shoulder, the whole seed 3-5mm (1/8-1/5in.) long. Flowers from August to October.
Habitat: Common ragweed is one of the most abundant weeds of cultivated land throughout southern Ontario, but is rare or absent in northern and northwestern parts of the province. It also occurs in gardens, flower borders, poorly kept lawns, edges of sidewalks, roadsides, fencelines, waste places, and in disturbed areas in pastures and meadows.

Similar Species: It is distinguished by its finely divided leaves, which are opposite in the lower part and alternate in the upper part of the plant, these being yellow-green at first, later gray-green with age, and its very numerous, tiny, non-showy, greenish male flower heads clustered along slender branches in the upper part of the plant.

It is essential that Goldenrod, Solidago spp., , not be confused with Common ragweed. Several species of Goldenrod occur throughout Ontario in meadows, pastures, woodland, river flats and roadsides, and have very conspicuous bright yellow inflorescences during the ragweed hayfever season of late summer and autumn. Goldenrods do produce pollen but only in small quantities, and their pollen is heavy and sticky. It is not carried on the wind and the plants are pollinated by insects. Because Goldenrod pollen is not carried on the wind, it must not be blamed as the source of irritation for ragweed hay fever sufferers.

Caution: Common ragweed is the most important cause of hay fever during August and September. Although inconspicuous and not recognized by most people, the tiny male flower beads hanging on their slender stalks produce huge quantities of very light pollen. As the pollen falls from these hanging flowers, it is caught by the wind and may be carried for distances greater than 200 km (125 miles). Hay fever sufferers, therefore, may be affected by pollen from ragweed plants far away.

Related Links

… on general Weed topics
… on weed identification, order OMAFRA Publication 505: Ontario Weeds
… on weed control, order OMAFRA Publication 75: Guide To Weed Control

| Back to the Ontario Weeds Gallery |

The Friends of the Wild Flower Garden, Inc.

Common Ragweed is a native erect annual, growing to 40 inches high with many upper branches. The stems are hairy and green to pinkish red.

The leaves are opposite lower, up to 4 inches long and alternate upper. They are 1-2 pinnatifid, that is once divided and the second division not fully cut to the central rib – feathery or fern-like in appearance, triangular in shape overall, fine hair on new leaves which dissipates with age. Leaf margins are usually smooth but they may have small teeth.

The floral array is a raceme like spike at the top of the stem containing numerous small green flower heads that look like green beads. The spike can be from 1 to 6 inches long and main stems many develop side shorter side spikes along side the main spike.

Flowers: The ‘green’ beads’ are the male flowers and they turn yellow to brown with maturity. Male and female flowers are separate. Each male flower has a cup-shaped head and is only 2 to 3 mm in diameter, 1/8 inch long with a short stalk no more than 1.5 mm long, and the flowers produce a yellow pollen that is wind dispersed. The male flower head has 12 to 20 florets and the outside of the head usually does not have black nerves visible like the Giant Ragweed does. Female flowers are whitish-green, have one floret with a branching style protruding. They are clustered in the leaf axils, obscured by leafy bracts, near and below the male flowers. The outside of the flower head of both sexes is enclosed in a series of green phyllaries (bracts) in several series.

Seeds: Fertile flowers produce small ovoid bur, that contains a 1/8 inch long cypsela (the seed) that has 3 to 5 spines and a short central beak. The bur is dispersed by clinging to fur or clothing. Cypselae are viable for several years.

Habitat: Common Ragweed grows in disturbed sites in wet to dry soils of many types. Full to partial sun is required. The root system is fibrous with deep branches.

Names: The genus, Ambrosia, is Greek for ‘food of the gods’ but explanations of this appellation to plants of this genus are lacking. The species, artemisiifolia, is more appropriate, meaning having leaves that resemble those of the Artemisia plant, which these do.

Comparisons: The closest ragweed in appearance to this species is the Western or Perennial ragweed, A. psilostachya, where the leaves are not as fern-like and per the name, it is a perennial. Giant Ragweed, A. trifida, is the other ragweed native to Minnesota, but there the plant is much taller and leaves are not fern-like.

Great Ragweed is a huge, coarse, native, erect, annual plant growing from 3 to 12 feet high, with occasional branching below the floral array. Stems are green with bristly white hair.

The leaves are opposite with 3 main veins and the larger leaves (up to 12 inches long and 8 inches wide) are palmately divided into 3 to 5 lobes. The margins are usually toothed and the leaf has a long winged stalk. Upper leaves are smaller and more lance shaped, usually with 3 lobes and also with a wing. The leaves have a rough surface.

The floral array is a cylindrical spike, up to 10 inches long, of many small, yellowish-green male flower heads shaped like beads. The main stems many develop shorter side spikes along side the main spike.

Flowers: Male and female flowers are composite and separate. The male florets (staminate) have a saucer-shaped head, 2 -4 mm in diameter and only 1/4 inch long and have a short stalk no more than 1 to 3+mm long. The five stamens of each floret produce a yellow pollen that is wind dispersed. The male flower head has 3 to 25 florets surrounded on the outside by a series of phyllaries that are rough on the outside and the head often has 1 to 3 black nerves visible. Male heads turn yellow to brown with maturity. Female (pistillate) flower heads are whitish-green, each containing one fertile floret. and clustered in small groups in the leaf axils near and below the male flowers. At the base of the floral array are several bract-like leaves.

Seeds: Fertile flowers produce small bur containing a pyramidal shaped, tough, 1/4 inch long (3 – 5 mm) cypsela that has 4 to 5 (sometimes 5 to 7) rounded spines (tubercles) and a short central beak; from the side the cypsela looks like a small crown, hence one of the older common names of ‘Crown Weed’. The bur is dispersed by clinging to fur or clothing. Cypselae are viable for several years. The tubercles contain air spaces allowing the seed to float on water and to be carried by the wind.

Habitat: Great Ragweed grows in disturbed sites in wet to dry loamy soils. Full sun to partial shade is tolerated. The root system is fibrous.

Names: The genus, Ambrosia, is Greek for ‘food of the gods’ but explanations of this appellation are lacking in understandability other than the genus is applied to a group of herbs that have high levels of wind borne pollen – some of which could be aromatic or sweet. The species, trifida, is appropriate, meaning having leaves that are three-cleft like the top leaves of this plant are. The author name for the plant classification – ‘L.’ refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.

Varieties: Older literature lists several varieties for this species, var. trifida for Minnesota as an example, but current botanical thinking places these as regional types of the same basic species, not different enough to separate. Both Flora of North America (Ref. #W7) and the Minnesota authorities at the U of M Herbarium (Ref. #28C) take this approach.

Comparisons: None of the other ragweeds approach in appearance this species. The others are smaller and with more fern-like foliage such as the Common Ragweed, A. artemisiifolia.

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Common ragweed: the plant is a pollen-producing machine. Photo: Getty

Ragweed is the super-villain of allergy plants, able to marshal millions of pollen grains and spread misery far and wide. But never fear! Allergic Living has the scoop on how to stop its dastardly effects.

IT’S OFTEN a hot, dry late summer’s evening spent relaxing out on a porch when the first telltale signs appear. An itchy, runny nose, irritated eyes, and a tingling mouth could indicate that you’re allergic to ragweed – one of the hardiest plants and most prolific pollen producers out there.

Often sprouting up on roadsides, in vacant lots, or anywhere with uneven ground, this weed is a major culprit for fall allergy symptoms. In 2009, the U.S. National Health survey found that 16 percent of Americans – about 49 million people – are sensitive to ragweed pollen. While its appearance is unremarkable, ragweed has special attributes that make it a formidable allergy foe.

Signs of the Allergy

Although most of us think of spring as pollen allergy season, approximately 45 percent of people with hay fever and asthma show signs of sensitivity to ragweed pollen. Depending on where you live – by mid-August in the north, and as late as October in the south – ragweed pollen levels peak as the days get shorter.

Noticeable symptoms are the classic itchy, runny or stuffed up nose; red, watery and itchy eyes, and maybe prickling mouth or ears, says Dr. Richard Weber, an allergist and aerobiologist at National Jewish Health in Denver. “You look around and a field where they took down an old house is now laying fallow and has a bunch of weeds in it. Sure enough, it’s ragweed.”

What is This Plant?

Giant ragweed: the species can reach 18 feet. Photo: Thinkstock

Although there are about 17 types of ragweed in North America, two species are the most abundant.

  • Common ragweed (Ambrosia artemisiifolia) can stand anywhere from a few inches high to 6 feet tall. It grows in tall, vertical tendrils with leaves divided into many fine lobes. When it flowers, rows of characteristic off-white blooms that look like upside-down tea cups appear.
  • Giant ragweed (Ambrosia trifida) has fewer and rounder leaves than common ragweed, and they usually have three distinct lobes, but can have up to five. Dangling similar stacks of inverted flowers, these plants can tower up to 18 feet.

Unlike fussier plants, ragweed can thrive in soil low in nutrients, and is a particular pain for farmers. Agricultural researchers have reports from farmers in several states who’ve found strains of ragweed resistant to glyphosate, one of the most widely used herbicides.

Not only does ragweed seem to grow anywhere, each annual weed produces enormous amounts of pollen – usually in the millions of grains. Designed to be aerodynamic, this pollen can travel thousands of miles from a parent plant. The pollen grains are released in clumps, held together with a sticky substance called pollenkitt, Weber explains. These clumps break apart in the air, allowing the grains to be distributed far and wide.

Unfortunately for those with allergies, ragweed pollen grains are also potent, and can prompt symptoms at counts of less than one pollen grain per cubic foot. Ragweed’s florets even have a bottlebrush-like mechanism to ensure the plant pushes out every last irritating pollen grain.

What It Isn’t

Goldenrod, left, commonly mistaken for ragweed, right. Photo: Getty

Goldenrod, another tall weed, sometimes unfairly takes the blame for early autumn allergies. It has showy yellow flowers that make it far more noticeable than plain-Jane ragweed. Goldenrod grows where ragweed thrives, and flowers at the same time.

When people see a mass of bright yellow fluff collecting, they think, “Look how sick I must be getting from that plant,” says Dr. Anne Ellis, an allergist in eastern Canada, a ragweed hotspot. Goldenrod churns out a small amount of sticky pollen, designed to be carried by insects, while ragweed produces vast amounts of pollen that is carried by the wind.

Where It Thrives and Its Season

Common ragweed grows in every state except Alaska. It’s even been introduced to Hawaii. Giant ragweed has been found everywhere except Alaska, Hawaii, and Nevada. Rates of ragweed allergy are highest in the Midwest and the northeast, because that’s where the plant truly thrives.

In most of North America, ragweed gets its cue to pollinate when the late summer days grow shorter. In the northern U.S. and Canada, it peaks in late August, and only frost takes down this mighty annual. In low-frost southern states, pollination can drag on into October.

Climate change is helping ragweed to endure. One telling study published in 2011 correlated weather data and pollen counts to find ragweed season had lengthened by two to four weeks over a 15-year period in northern U.S. and Canadian sites. No matter where you are, at times ragweed feels inescapable.

Weather Effects

A soggy spring is not a good omen for ragweed allergy. More moisture in spring and summer will lead to larger ragweed plants able to churn out more pollen. As with grass and tree pollen, ragweed pollen is more likely to be grounded by moisture on a wet, drizzly day, so that’s a perfect time to venture out. Watch out for hot, dry, windy days when the grains are sure to be whizzing around.

Photo: Thinkstock

What You Can Do
  • Confirm the culprit: To verify a ragweed allergy, see an allergist who will look for a combination of a positive skin test or blood test while asking you about any allergic rhinitis or asthma symptoms. Weber says a key sign is the timing and severity of symptoms compared with local pollen counts. Since house dust mite and outdoor mold allergies can also flare at the same time of year, the allergist needs to investigate whether ragweed is truly your problem.
  • Nasal sprays: Since we all like to get outside, a good defense against allergic rhinitis is nasal corticosteroid sprays, “but you have to plan ahead,” says Weber. The sprays work best if you start using them regularly a couple of weeks before pollen season begins. “People don’t do that,” Weber says. “They wait until they’re suffering. Then, they wonder why they’re suffering.” Two of those sprays, Nasacort and Flonase, are now available over the counter in pharmacies.
  • Antihistamines: Although they won’t block the biochemical cascade set off during an allergic reaction, some people find non-sedating antihistamines are helpful to keep symptoms at bay.
  • Immunotherapy Options: Allergy shots are an option for those who are walloped by ragweed year after year. It takes about five years, and many needles, but evidence suggests the benefits can last a lifetime.

For those who cringe at the notion of needles, an under-the-tongue tablet called Ragwitek may offer relief. Like allergy shots, the prescription drug works by desensitizing the immune system to ragweed pollen. To get the best protection, Ellis advises starting the tablets daily as early as April and taking them until the end of ragweed season. Research has found the sublingual tablets are nearly as effective as allergy shots, and have fewer serious side effects.

Ragweed Avoidance
  • Taking extra steps to stop ragweed pollen from getting inside is worth the effort.
  • Keep windows closed and use an air conditioner with a HEPA filter on hot days.
  • Ragweed is a late-morning pollinator, making early morning a better time to get outside. Rain also keeps it grounded.
  • Get rid of ragweed on your own property by simply plucking the plants out at the root – preferably before pollination starts. (If you have the allergy, wear a mask).
  • After being outdoors, change clothes right away, and shower if time allows.
  • Washing (or at least brushing) pets after they’ve played outside can reduce pollen tracked indoors.
  • Use the dryer in pollen season, as hanging clothes out to dry collects allergens.

Dodging pollen in the first place to prevent reactions can be just as important as finding effective treatments. So take the time and get creative about minimizing your exposure to ragweed’s abundant pollen.

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The Reality of Your Ragweed Allergy

What Is Ragweed?

Ragweed is a member of the daisy family and has tiny yellow-green flowers that produce vast amounts of pollen – about a million grains per plant, every single day.

Where Does Ragweed Grow?

Ragweed is found in fields, gardens, roadsides and waste areas all over the U.S., but it is the biggest problem in the East and Midwest.

When Does Ragweed Bloom?

Ragweed grows from August to November, peaking mid-September and ending with the first frost. However, if you get allergies from ragweed, you might have noticed your symptoms are lasting longer every year.

How Does Ragweed Pollen Move?

Ragweed pollen grains are so light that they can travel up to 400 miles in the wind. This means that when it comes to ragweed spreading across the country, the sky’s the limit.

Why Does Ragweed Pollen Cause Allergic Reactions?

People with allergies might have more sensitive immune systems that fight allergens, thinking they’re harmful foreign substances, such as viruses or bacteria. When you have a ragweed allergy and breathe in the pollen, your body defends itself against the invader (even though it might be harmless), and the reaction leads to allergy symptoms.

Ragweed Allergy Symptoms

The most common ragweed allergy symptom is a stuffy or runny nose, but you also might experience sneezing, itchy eyes, watery eyes and other common allergy symptoms.

Ragweed Allergy Treatment

  1. Stay one step ahead of ragweed. ZYRTEC® ALLERGYCAST® app shows you what pollen is in the air with the daily pollen forecast and you can track your allergy symptoms, too. Standard data rates for your plan apply.
  2. Cover up. When outside, wear hats, gloves, glasses, paper masks and long-sleeve shirts to prevent contact with ragweed and other pollens.
  3. Remove your shoes. Kick your shoes off before entering your home to avoid tracking ragweed and other pollens inside.
  4. Take a shower. After long periods outdoors, showering will help remove ragweed and other pollens from your skin and hair.
  5. Try an antihistamine. ZYRTEC® is a common antihistamine that helps relieve your worst ragweed allergy symptoms. It starts working at hour 1 and stays strong day after day. Learn more about the ZYRTEC® family of products.

If you’re suffering from hay fever symptoms in the late summer or fall, consult an allergist about the possibility of a ragweed allergy. Your allergist can confirm a diagnosis with a skin test — applying a diluted allergen to the surface of your skin and waiting about 15 minutes to see if there is a reaction, such as a raised red bump that itches.

Ragweed allergies can be treated with antihistamines and other allergy medications. As with pollen season in the spring, you can try to get ahead of these allergies by starting your medication two weeks before you expect your symptoms to be at their worst. Ask your allergist whether any of your medications can be taken before symptoms develop.

Two immunotherapy options are available for severe cases of ragweed allergy:

  • Allergy shots can help your body build resistance.
  • Tablets that dissolve under your tongue are available by prescription. Pills must be started 12 weeks before the beginning of ragweed season.

Other tips include:

  • To avoid pollen, know which pollens you are sensitive to and then check pollen counts. In spring and summer, during tree and grass pollen season, levels are highest in the evening. In late summer and early fall, during ragweed pollen season, levels are highest in the morning.
  • Keep your windows closed at all times, both at home and in the car.
  • Remember that pollen can be tracked into your home via your clothes, your hair or your pet — so change your clothes after being outside for long periods of time, shower before going to bed and wash your hands after petting an animal that has been outside.

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