Common names: Common ragweed, annual ragweed, hogweed, hay-fever weed, Roman wormweed, and bitterweed.
Latin name: Ambrosia artemisiifolia L.
“Ambrosia” is from Greek mythology and refers to the food or drink of the gods, often associated with granting immortality. Meanwhile, “artemisiifolia” indicates that the foliage of common ragweed looks like the foliage of plants from the Artemisia genus, such as wormwood.
Family: Asteraceae (the sunflower family)
General Description and Life Cycle
Common ragweed is a summer annual found across Indiana and the Midwest. It reproduces by seeds and has an upright growth habit with a central leader and many branches. Globally common ragweed populations have been confirmed resistant to WSSA herbicide Groups 2, 5, 9, and 14. Populations resistant to glyphosate (the active ingredient in Roundup) have been documented across the United States, and there are reports of atrazine-resistant populations in the United States and Canada.
Identification
Seedlings emerge with two thick, round cotyledons (seed leaves) (Figure 1). True leaves initially appear in pairs on opposite sides of the stem but eventually become alternate and staggered along the stem. Common ragweed leaves have a deeply cut and fine, almost fern-like, texture (Figures 2 and 3). Plants contain both male and female flowers. Male flowers appear on flower stalks (racemes) at the end of the stems, while female flowers are nestled into the leaf axils at the top of the plant (Figure 4). Seeds are small and appear in crown-shaped fruit approximately 3 mm long. The fruit largely resembles a scaled-down version of giant ragweed fruit (Figure 5).
Figure 1. Common ragweed seed leaves (cotyledons) (Photo by S.L. Meyers).
Figures 2. Common ragweed leaves appear fern-like (Photos by S.L. Meyers).
Figures 3. Common ragweed leaves appear fern-like (Photos by S.L. Meyers).
Figure 4. Male flowers appear on racemes at the top of the plant and female flowers appear in axils on upper branches (Photo by S.L. Meyers).
Figure 5. Common ragweed fruits and one giant ragweed fruit for comparison (Photo by S.L. Meyers).
Interesting facts
Pollen from common ragweed is carried in the wind and is a major contributor to hay fever in the late summer and early fall. Because common ragweed flowers are not showy, hay fever symptoms are often incorrectly blamed on goldenrod, which flowers at the same time and has highly visible, bright yellow flowers. Some allergy medicine companies have used this misunderstanding to market their products (Figure 6).
Figure 6. An allergy medicine with an image of goldenrod, often blamed for hay fever allergies caused by common ragweed. Source: Customer Reviews: CVS Health Allergy Relief Diphenhydramine Tablets – CVS Pharmacy
Management
Common ragweed can be managed with control measures used for other summer annual broadleaf weeds. Many of these are covered in previous weed spotlight articles and include preplant and in-season cultivation, hoeing, or hand-removal. Inversion tillage (moldboard plowing) can bury the small seeds deep in the soil and prevent their germination, but this should be used sparingly. Fall-planted cover crops, such as cereal rye that are terminated in the spring by mowing or roller-crimping can provide suppression if enough cover crop residue is present on the soil surface. Plant-based and plastic mulches and silage tarps are also very effective. Given the presence of resistance to numerous herbicides applied to emerged ragweed plants, herbicide-based weed management programs should include a pre-emergence, soil-applied herbicide as well. For more information on managing common ragweed in the vegetables you grow, consult the Midwest Vegetable Production Guide at mwveguide.org.
References
Heap, I. The International Herbicide-Resistant Weed Database. Online. Wednesday, August 21, 2024. Available www.weedscience.org
Neal, J.C., Uva, R.H., DiTommaso, J. M., DiTommaso, A. 2023. Weeds of the Northeast. Second edition by Cornell University.