Common ragweed and giant ragweed are annual broadleaf weeds that contain both male and female flowers. Characteristics such as size and leaf shape differ between common ragweed and giant ragweed.
Common ragweed (Ambrosia artemisiifolia) is an annual broadleaf weed found across most of the United States. Common ragweed is a difficult-to-control and hardy weed that can withstand adverse environmental conditions.
Giant ragweed (Ambrosia trifida) also poses a significant threat to crop yields. Although the weed can infest fields throughout the Midwest, giant ragweed causes more problems for farmers in the Eastern Corn Belt.
Ragweed thrives under many environmental conditions, such as roadsides, fencerows and high-yield cropland. Ragweed management is a challenge as it aggressively competes with crops and adapts quickly to farming practices.
Common ragweed seedling stems and seed leaves are green and often splotched with purple. Seed leaves, or cotyledons, grow 1/4-inch long and are round. The distinctive shape of ragweed appears with the first true leaves, which feature deep cuts in the margins and pointed tips. Leaves and stems are covered with small, white hairs.
Common ragweed produces 1/8-inch long seeds in late August through September. Each plant emerging in May can produce 30,000 to 62,000 seeds. Amazingly, seeds that are buried in the soil can live in the soil seedbank for four decades or longer. Common ragweed features shallow roots and can grow 2 to 4 feet tall. Stems can be hairless and usually are bushy. Leaves can grow 6 to 12 inches long and up to 6 inches wide.
Giant ragweed has a different size and leaf shape than common ragweed. Giant ragweed produces large seeds that are shaped like crowns, with points and ridges along the top. A single plant can produce up to 5,100 seeds. The seed leaves of giant ragweed grow more than 1 inch in length. The first true leaves are not deeply indented. Giant ragweed also features three-lobed leaves that grow opposite from each other on the stem. When mature, giant ragweed can grow up to 17 feet tall; it often grows 1 to 5 feet taller than the crop with which it is competing.
Manage Tough-to-control and Resistant Ragweed
With its tough competition potential, it’s best to aggressively control ragweed and manage resistance. Similar to most problem weeds that can rob crop yields, ragweed control requires season-long management. It is recommended to control ragweed when weeds are less than 4 inches tall.
- In fields with a history of ragweed problems, spray in the fall if ragweed seedlings are observed. The primary goal of a fall treatment is control of emerged plants, but it is not a substitute for a preplant herbicide treatment the following spring. An application of burndown and residual herbicides is still required closer to the time of planting in fields that were treated in the fall.
- Failure to treat ragweed-infested fields in the fall can result in a population of overwintered ragweed plants the following spring, which should be controlled early in the spring to ensure effective burndown. Apply burndown herbicides at that time with some of the residual herbicide and, at planting, apply the rest of the residual herbicide. The at-planting residual herbicide application might require some additional burndown herbicide.
- Tillage near the time of planting effectively removes ragweed if it thoroughly mixes the upper few inches of soil and uproots existing plants. Tillage can reduce heavy ragweed infestations if options besides rotation and burndown are warranted.
Known Resistance in Ragweed
Resistant issues. Common ragweed resistance is documented to PSII (5), ALS (2), EPSP (9) and PPO (14) chemistry groups, and giant ragweed resistance is documented to ALS (2) and glyphosate (9) chemistry groups.
For more information on ragweed and other resistant weeds confirmed by state, refer to the International Survey of Herbicide Resistant Weeds.
Potential Damage and Economic Impact
Ragweed is highly competitive in corn, soybeans, cotton, wheat and other cereals, siphoning moisture and nutrients away from the crop and reducing yields. Heavy ragweed populations can substantially reduce yields in some cases.
- In a publication by Purdue University, researchers noted that competition from just two giant ragweed plants per 110 square feet reduced corn yield by 13 percent. And one plant per 110 square feet reduced soybean yields by 50 percent.
- Giant and common ragweed, johnsongrass and marestail all produce spring growth that can reduce winter wheat harvesting efficiency and may lead to dockage from increased moisture and foreign matter. Following wheat harvest, weeds may survive and be difficult to control in double-cropped soybeans.
- A study by the University of Tennessee found that populations of giant ragweed could delay maturity of cotton plants and reduce lint yield by 50 percent, although fiber quality was not affected. The study showed that a ragweed plant could impact plants at least three feet away.
Bayer has a broad portfolio to combat tough-to-control and resistant weeds. A well-thought-out herbicide program, using multiple modes of action, should be implemented to manage weeds. Before applying any herbicide, please read the entire label and follow label instructions for the best possible results and to confirm that the product is effective on the weeds you wish to control. Not every product is suitable for every situation, and use of the correct application technique will ensure the best results.
Please visit our corn and soybean pages for information on a portfolio of products from Bayer to help you better manage weeds.