A Tale of Two Broadleaf Weeds: Giant and Common Ragweed

February 24, 2020

common ragweed seedling
When left unmanaged, common ragweed can cause devastating yield losses in corn.

Growing season. It’s the best of times. But if you don’t protect your yields from prolific weeds, it can also be the worst of times.

Two prolific, broadleaf weeds that threaten your yields are giant ragweed and common ragweed. By learning the key characteristics of each, as well as management strategies, you can help ensure that your growing season is truly the best of times for your crop.


The problem of ragweed

Prevalent throughout the Midwest, both giant ragweed and common ragweed can cause yield losses. Both varieties are monoecious, having separate male and female flowers on the same plant. This allows for cross-pollination that leads to much variation in genetic diversity and a greater potential for herbicide resistance. While there are some similarities, the two ragweed varieties have key differences that make them problematic.

Giant Ragweed

Emerging late in March and blooming from July through October, giant ragweed has the potential to grow up to 16 feet tall in fertile soils. This weed has an initial competitive advantage over crops due to its fast growth rate. Giant ragweed is more prevalent in tilled fields, as tillage mixes the seeds into the soil where they can escape predation. It is common for seedlings to emerge from as far as four inches below the surface. Mature giant ragweed plants can produce up to 5,100 seeds.i If left unmanaged, one giant ragweed plant per ten square feet can reduce yield up to 55 percent in corn.ii

Common Ragweed

Common ragweed is a summer annual that can grow three to six feet tall. It thrives in low-fertility soil and is most prevalent in fields with reduced- or no-till practices. At full maturity, a single common ragweed plant can produce up to 62,000 seeds that can be added to the weed seed bank. If left unmanaged, a weed density of five common ragweed plants per acre can result in yield losses of up to 21 percent in corn.iii


Identification

Proper identification of ragweed is essential for selecting strategies that will manage and control your problem weeds.

Giant Ragweed

giant ragweed
Young giant ragweed plant. Photo courtesy of Theodore Webster, USDA Agricultural Research Service, Bugwood.org.

To identify giant ragweed, look for:iv

  • Hairy stems
  • Round, thick cotyledons with a purple hypocotyl
  • Hairy leaves that are four to eight inches wide and six inches long and have opposite arrangement around the stem
  • Leaves that are cut into three or five lobes with toothed edges
  • Green flowers with small, slender stems at the end of branches or bases of upper leaves

Common Ragweed

common ragweed
Young common ragweed plant.

To identify common ragweed, look for the following characteristics:iii

  • Hairy stems
  • Leaves that are four inches wide and six inches long and have opposite arrangement around the stem
  • Compound leaves, that are cut into lobes and wider at the base than the tip
  • Young leaves with hairs on the undersides
  • Mature leaves that are relatively hairless

Strategies for managing ragweed

“Implementing an integrated weed management program is one of the best things a grower can do to manage prolific weeds, like ragweed,” said Frank Rittemann, selective corn herbicides product manager at Bayer. “This involves taking a zero tolerance approach to ensure that no weed is allowed to produce seeds that could add to the weed seed bank and impact future growing seasons.”

To take a zero tolerance approach, incorporate a variety of strategies to take out weeds before they can produce seeds, generally before they are three inches tall. Some beneficial strategies include:

  • Tillage practices

    Pre-plant tillage practices can reduce the number of early emerged common ragweed seedlings in your fields. For fields that do not yet have emerged common ragweed, it is recommended to till at night as tillage during the day can stimulate seedling germination.v

    Tillage can also be used to manage giant ragweed seedlings; however, this practice may also increase germination of giant ragweed. This weed does not respond to night tillage. To manage giant ragweed before it emerges, strict no-till practices can be beneficial, leaving the seeds on the surface, subject to predation.vi

  • Herbicides

    Herbicides are an essential management strategy for both giant and common ragweed. Use a two-pass program that consists of a strong pre-emergence herbicide application with residual as well as a postemergence application to take out ragweed plants before they go to seed.

  • Scouting

    A couple of weeks following each herbicide application, it is a good idea to scout your fields and identify giant and common ragweed. If there are any ragweed plants remaining after the postemergence application, you may consider pulling them before they can add to the weed seed bank.


Bayer solutions for managing ragweed

Rittemann recommends using a two-pass herbicide program to take a zero tolerance approach to control giant and common ragweed.

Corvus® herbicide (Groups 2 and 27), tankmixed with Harness® Xtra herbicide (Groups 5 and 15), utilizes four sites of action to start with cleaner fields at time of planting. Corvus also provides the power of reactivation, where one of its residuals, isoxaflutole, is reactivated with as little as one-half inch rain to help control of emerged weeds.

DiFlexx® DUO herbicide (Groups 4 and 27), tankmixed with a Roundup® Brand agricultural herbicide (Group 9), features three unique sites of action to take out tough-to-control weeds, like ragweed, at postemergence. DiFlexx DUO can be applied up to the V10 stage of development to halt late-season weeds before they go to seed.

This two-pass herbicide program provides control of ragweed to help you keep your fields clean and weed-free. As part of an integrated weed management program, Corvus and DiFlexx DUO help control weeds before they set seed to minimize escapes and protect your fields for the future.



ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Corvus® and Harness® Xtra are restricted use pesticides. Not all products are registered in all states and may be subject to use restrictions. The distribution, sale, or use of an unregistered pesticide is a violation of federal and/or state law and is strictly prohibited. Check with your local dealer or representative for the product registration status in your state. Bayer, the Bayer Cross, Corvus, DiFlexx, Harness and Roundup are registered trademarks of Bayer Group. For additional product information call toll-free 1-866-99-BAYER (1-866-992-2937) or visit our website at www.BayerCropScience.us. Bayer CropScience LP, 800 North Lindbergh Boulevard, St. Louis, MO 63167. ©2020 Bayer Group. All rights reserved.



Sources:

i Johnson, B., Loux, M., Nordby, D., Sprague, C., Nice, G., Westhoven, A., and Stachler, J. “Biology and Management of Giant Ragweed.” Purdue Extension, 2007. https://weedscience.missouri.edu/publications/gwc-12.pdf

ii “Giant ragweed.” Michigan State University Extension. https://www.canr.msu.edu/weeds/extension/giant-ragweed

iii Brown, C., Follings, J., Moran, M., and Rosser, B. “Weed Control.” Agronomy Guide for Field Crops, 2017. http://www.omafra.gov.on.ca/english/crops/pub811/pub811ch13.pdf

iv Jordan, T., Nice, G., Smeda, R., Sprague, C., Loux, M., and Johnson, B. “Biology and Management of Common Ragweed.” Purdue Extension, 2010. https://weedscience.missouri.edu/publications/gwc-14.pdf

v Barnes, E., Werle, R., Sandell, L., Lindquist, J., Knezevic, S., and Jhala, A. “Preplant Tillage to Manage Glyphosate-resistant Common Ragweed.” University of Nebraska – Lincoln CropWatch, 2018. https://cropwatch.unl.edu/2018/preplant-tillage-manage-glyphosate-resistant-common-ragweed

vi “Ragweed, Giant.” GROW: Getting Rid of Weeds Through Integrated Weed Management. http://integratedweedmanagement.org/index.php/search-weeds/ragweed-giant/

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