Submitted to: Illinois Crop Protection Workshop Proceedings
Publication Type: Proceedings
Publication Acceptance Date: December 20, 2001
Publication Date: N/A
Technical Abstract: Giant ragweed is a native of the Midwest and is one of the most troublesome weeds in corn/soybean rotations in some locations. Early research showed that virtually all giant ragweed seeds germinated very early in the season. Tillage and planting resulted in relatively few giant ragweed problems in most fields. In the 1970s this weed was found mainly in undisturbed areas and sometimes in fields in flood plains. Especially over the last decade, giant ragweed has spread throughout fields in many areas. Giant ragweed is one of the most competitive weeds found in corn and soybeans. Research in recent years has shown that the emergence period of giant ragweed appears to be shifting to a later germination pattern, resulting in greater problems. Other factors, such as earlier planting and less tillage before planting also contribute to the problem. Control with herbicides can be very good, but often is inconsistent, with many soil applied herbicides, since the weed can emerge from considerable depths and at various times. Postemergence control may be inconsistent because the weed often gets too large and then regrows after treatment, as well as emerging after treatments are completed. The development of resistance to some herbicides has limited the options in some areas. Giant ragweed seeds can remain viable for a number of years in the soil. Heavy infestations likely will require using a management program for several years for optimum results. Undisturbed areas near fields often provide the source of seed for spread into fields. Current research is investigating the emergence and longevity of giant ragweed seeds, aspects of competition, and improved management systems.