Ambrosia artemisiifolia is an annual herbaceous plant that grows 150 cm tall. The stem is erect, heavily branched, glabrous, and pinkish-red in color.
It is easily recognizable by its deeply lobed compound leaves that have a fern-like appearance and can cause allergic reactions in some people on contact.
Annual Ragweed Classification
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Asterales
- Family: Asteraceae
- Genus: Ambrosia
- Species: Ambrosia artemisiifolia
- Varieties: Ambrosia artemisiifolia var. elatior and Ambrosia artemisiifolia var. paniculata
- Common Names: Ragweed, Common ragweed, Carrot weed, Hay Fever weed, Hogweed, Short ragweed, American wormwood, Tassel weed, Blackweed, and Bitterweed.
Nativity and Distribution
Annual ragweed is native to North and Central America. It is now found in parts of:
- Africa
- Asia
- Australia
- Europe
- Australia
Physical Characteristics
- Leaves: Opposite or alternate with a fern-like appearance.
- Fruits: Woody, green to brown fruit with spike-like projections.
- Stems: Erect, heavily branched, and can grow 1.5m tall.
- Flowers: Inconspicuous yellow to brown flowers.
- Roots: Taproot system.
Ambrosia artemisiifolia is a summer annual herbaceous weed that can grow 1.5m tall. It is easily recognizable by its alternate or opposite, deeply lobed leaves with a delicate fern-like appearance.
The stems are upright, slender, heavily branched, pubescent, and pinkish-red in color. The leaves are opposite or alternate with lanceolate or elliptic leaf blades about 3-12 cm long.
Annual ragweed produces greenish-white inconspicuous flowers found on spine-like terminal branches. Blooming occurs from July to October, producing a prolific amount of pollen that is easily carried away by wind.
The seeds are egg-shaped, wrinkled, about 1.5mm wide and 1.5-3.0mm long, and brown in color.
Reproduction, Dispersal, and Life Cycle
- Life Cycle: Annual.
- Seeds: A plant that grows for the entire season can produce over 30,000 seeds.
- Climate: Temperate continental climate.
- Dispersal: Wind, water, animals, and human activities.
Annual ragweed behaves as an annual weed and mainly reproduces by seeds. It is a prolific seed producer with a single plant producing over 30,000 seeds in one growing season.
The seeds are small and lightweight and thus mainly dispersed by wind. However, they can also be dispersed by water, birds, through agricultural practices, and as a contaminant of cereals, oil grains, and bird seed.
Seeds that fall on the surface germinate easily. Seeds buried underground can remain viable for up to 40 years. Tillage brings the dormant seeds to the surface, promoting widespread growth of the weed.
Similar Plants
- Ambrosia acanthicarpia
- Ambrosia annua
- Ambrosia trifida
- Ambrosia psilostaychia
Uses
- It is used as a medicinal plant for treating fevers, nausea, and skin problems.
- It is used to get rid of heavy metals such as lead and cadmium (phytoremediation) in the soil.
- It is used as fodder for sheep and goats.
- The oil from its seeds is used to make paints and varnishes.
- Root extract is used to treat menstrual disorders.
- The pollen is used to formulate treatments for allergies to the plant.
Impact on Farms and Environment
Annual ragweed is a pernicious weed that severely impacts agricultural lands. It reduces crop quality and yield with documented losses ranging between 10-70% loss. Some of the most affected crops include maize, cotton, sunflower, and soybean.
It is considered one of the most invasive and notorious weeds due to its prolific seed production, rapid growth, and competitive nature. It emerges among the pioneering summer weeds that compete with native plants and quickly colonize new areas, resulting in decreased biodiversity.
As the name hay fever weed implies, it is one of the biggest causes of hay fever and seasonal rhinitis, with the uncomfortable symptoms lasting 2-3 weeks. The ragweed pollen can also cause contact dermatitis and conjunctivitis.
Annual ragweed is also toxic to cattle, causing nausea and changes to milk flavor.
Control
- Mechanical control: Hand weeding, mowing, crushing, and mechanical cutting.
- Cultural control: Planting red clover as a cover crop.
- Chemical control: Pre-emergence herbicides like mesotrione, atrazine, and flurochloridone and post-emergence herbicides like glyphosate, dicamba, 2,4-D, and metsulfuron-methyl.
- Biological control: Essential oils from clove, cinnamon, red thyme, and summer savory.
Hand weeding, mechanical cutting, and mowing (at 2 cm from the soil) can help control annual ragweed by reducing seed and pollen production. However, due to its large infestations and persistence, it may be the most expensive control method.
Intercropping a cover crop like red clover with a cash crop such as wheat can help suppress in-season weeds like annual ragweed.
Numerous herbicides can provide effective control against Ambrosia artemisiifolia. Pre-emergence herbicides like mesotrione have been shown to provide over 80% eradication of the weed. Other herbicides like flumioxazin and metribuzin applications have provided successful control in soybean plantations.
Post-emergent herbicide combinations of dicamba, triasulfuron, metsulfuron-methyl, and 2,4-D can help eradicate the weed in spring barley. Other herbicides like paraquat, bentazone, and imazapic are used to control common ragweed in peanut farms.
Refer to the CABI compendium for further information on herbicide applications for different cash crops. Consult a professional if you’re unsure what herbicides to use for your farm or landscape.
Numerous biological agents have been released in an attempt to control the invasive weed. Some like Zygrogramma suturalis (ambrosia striped leaf beetle) have provided slow and moderate success.
However, other agents like Phyllachora ambrosia and septoria epambrosiae are still under research.
Current biological agents in use for control of Ambrosia artemisiifolia include essential oils from plants like clove, cinnamon, red thyme, and summer savory.
Lead Editor for Insight Weeds.