WEED OF THE MONTH: Giant Ragweed

Trends:

  • Previous cases of giant ragweed typically have been found in undisturbed areas, such as fencerows and ditches. Over the past two decades, giant ragweed populations have spread and become problematic to many fields across the Corn Belt.3
  • These three factors are commonly mentioned as causes of increased giant ragweed prevalence:3
    • Crop rotation and tillage
    • The influence of stem-boring insects on herbicide efficacy
    • Herbicide resistance

Resistance statistics:*

According to WeedScience.org:

  • Herbicide classes:

– ALS inhibitors:

– IA, IL, IN, OH

– Glycine (glyphosate):

– AR, IA, IN, KS, MN, MO, MS, NE, OH, TN, WI

  • Multiple resistances:

– ALS inhibitors and glyphosate:

– MN, MO, OH

*Resistance confirmation does not necessarily include all weeds and may vary among different areas of each state.

Weed management tips:

Scott Ditmarsen, field scientist, Dow AgroSciences, says:

  • Scout early. Giant ragweed has an early and extended germination period, so begin scouting early in the growing season. Pay close attention to areas in fields with richer soils that have higher levels of organic matter.
  • Utilize multiple modes of action. Giant ragweed is extremely competitive and at full maturity can reach a height of eight feet. It is difficult to control with a single soil or postemergence herbicide application. For best control, growers should utilize both pre- and postemergence treatments. A burndown herbicide and/or aggressive tillage prior to planting are the most effective ways to eliminate early germinating plants that can out-compete the crop.

Dow AgroSciences weed control solutions:

Corn:

*Regulatory approvals are pending for the Enlist herbicide solution and crops containing Enlist herbicide tolerance traits. This is not an offer for sale of Enlist.

Soybean:

*Regulatory approvals are pending for the Enlist herbicide solution and crops containing Enlist herbicide tolerance traits. This is not an offer for sale of Enlist.

Additional information:

1PLANTS Profile. U.S. Department of Agriculture Natural Resources and Conservation Service website. http://plants.usda.gov.
2MSU Weed Science: Giant Ragweed. http://www.msuweeds.com/worst-weeds/giant-ragweed/.
3Biology and Management of Giant Ragweed. http://www.extension.purdue.edu/extmedia/BP/GWC-12.pdf.

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