Spread of giant ragweed across the North Central Region
The timing of giant ragweed emergence varied across the region with giant ragweed emerging earlier and for a longer period of time in the east-central region of the Corn Belt (i.e., Ohio and Indiana) than in other areas. Difficulty of managing giant ragweed was associated with its presence in waterways, and with an earlier and longer emergence period.
Reduced use of conventional tillage in corn and soybean fields was associated with increased difficulty of managing giant ragweed. Based on these results, it appears that giant ragweed first became a problem weed in the east-central region of the Corn Belt and is now becoming established in crop fields in areas outside of that region, especially toward the North and West. It is likely that giant ragweed spreads initially through a variety of non-crop edge habitats and then becomes established in areas adjacent to crop fields such as waterways and fencerows, and from there it can quickly get established in crop fields.
Giant ragweed emergence characteristics and reduced tillage both play a role in the development of giant ragweed as a problem weed in crop fields. Late-emerging giant ragweed genotypes that create the most problems for soybean growers are prevalent in Ohio, likely due in part to a combination of reduced tillage and earlier crop planting dates over the past several decades.