University of Illinois

No. 13/June 20, 1997

Replanting Herbicide-Resistant/Tolerant Soybeans

Prolonged cool soil temperatures and abundant moisture have contributed to areas of some soybean fields having to be replanted (often the perennial "wet hole"). Undoubtedly, some of these fields were originally planted with a herbicideresistant/tolerant soybean variety. The supply of seed for replant of these particular varieties may be in short enough supply to force producers into replanting the "wet holes" with a conventional soybean variety, not a resistant/tolerant variety. If this is the case, weed control strategies will need to be modified somewhat.

Roundup Ready and STS soybeans are currently the only commercially available herbicide-resistant/tolerant varieties. Roundup Ultra would be the preferred choice of growers with Roundup Ready soybeans; but if areas of a field were replanted with non-Roundup Ready soybeans, weeds in these areas would have to be controlled by some option other than Roundup. Synchrony STS is labeled for use only on sulfonylurea-tolerant soybeans (STS), so if areas of STS fields are replanted with a non-STS variety, Synchrony should not be applied to the non-STS soybeans.
What can be done for weed control if the replanted areas are not the same or a similar resistant/tolerant variety was planted originally? Obviously, many options exist for chemical and nonchemical control. A soil-applied herbicide may provide sufficient control to eliminate the need for a postemergence herbicide application. If a postemergence program is desired, products other than Roundup Ultra or Synchrony STS could be used in the non-resistant/tolerant replanted areas or across the entire field. If Roundup Ultra or Synchrony STS is to be used, make sure the replanted areas are clearly defined so these products are not applied to the nonresistant/tolerant soybeans.

Aaron Hager and Marshal McGlamery, Department of Crop Sciences, (217)333-4424