Survey provides management insight on giant ragweed

Nearly 60% of counties have giant ragweed populations resistant to mainstream herbicides.

A new survey published in the journal Weed Science offers insights into the distribution and management of giant ragweed, a plant known to cause significant losses in corn, soybean and cotton crops.

Over the past three decades, giant ragweed has become an increasing concern, especially as herbicide-resistant populations have increased. To date, though, scientists have lacked quantitative data on how giant ragweed is distributed and spreads.

To help address this gap, a team of researchers from six universities and the U.S. Department of Agricutlure’s Agricultural Research Service surveyed certified crop advisers working in the Corn Belt regions of the U.S. and Canada. The survey explored the prevalence of giant ragweed and gathered information on crop production practices. The responses led to several key findings.

Results suggested that giant ragweed is spreading outward from crop fields in the east-central U.S. Corn Belt. The weed currently is most prolific near the upper Mississippi River and its major tributaries, as well as north of the Ohio River in Indiana and western Ohio.

Nearly 60% of counties represented in the survey have giant ragweed populations that are resistant to ALS-inhibiting herbicides, to glyphosate or to both.

Results also showed that giant ragweed populations are highest in fields that are managed with minimum tillage, planted continuously with soybean crops and treated with multiple applications of a single type of herbicide.

The abundance of giant ragweed in crop fields was also highly correlated with its abundance in nearby non-crop environments. Populations of giant ragweed were highest in counties that offered early and prolonged periods of emergence and in crop fields with large populations of seed-burying earthworms.

Emily Regnier of Ohio State University, a member of the research team, said managing giant ragweed in non-crop areas could reduce its migration into crop fields and slow its spread.

“Where the weed is already established in crop fields, it is critical that growers focus on diversification,” she said. “They need to plant a more diverse combination of crop species, use more diverse tillage practices and reduce their reliance on herbicides with a single site of action.”

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