Soybean Herbicides for 1999

April 2, 1999
Although there are several new herbicides labeled for use in corn, no new active ingredients are currently registered for use in soybeans for the 1999 season. There are, however, some changes to note with certain registered soybean herbicides.

Axiom 68DF (flufenacet + metribuzin) can be used in both corn and soybean to control certain annual grass and broadleaf weed species. Keep in mind that the product use rates for these crops are not identical. Specifically, the use rate range of Axiom when used in corn is 13 to 23 ounces per acre, whereas the range when used in soybeans is only 7 to 13 ounces per acre. It is reasonable to expect that weed control with the soybean use rates may be less than what can be achieved with the higher rates used in corn.

Liberty (glufosinate) is currently registered for weed control in glufosinate–resistant (Liberty Link) soybean varieties. However, AgrEvo has elected not to commercialize Liberty Link soybeans for the 1999 growing season. Concerns about the seeds of these genetically modified organisms (GMO) entering foreign markets that have yet to approve their import have been a contributing factor to the delayed introduction of Liberty Link soybeans.

As mentioned in the previous issue of this Bulletin, Clarity (dicamba) has received a label for use prior to planting soybeans. Specifically, 4 to 16 fluid ounces of Clarity may be applied prior to planting soybeans. Following a Clarity application up to 8 fluid ounces, a minimum accumulation of 1 inch of precipitation and a waiting interval of 14 days must occur prior to planting. The waiting interval increases to 28 days (and still requires 1 inch precipitation) for applications of Clarity greater than 8 fluid ounces. Failure to adhere to these precipitation and time restrictions greatly increases the probability of soybean injury. Since Clarity is now labeled for use prior to planting soybean, replanting a lost corn crop previously treated with Clarity to soybeans could now be considered an option, given all precipitation and time restrictions have been satisfied.

Authority 75DF (sulfentrazone) may be applied prior to planting soybeans. In previous years, sulfentrazone has not been available as a single–entity product. Rather, sulfentrazone could have been obtained in the products Authority Broadleaf (Authority + Classic), Canopy XL (Authority + Classic), Cover, and Authority First/Synchrony STS (a co–pack of Authority and Synchrony STS). Through an agreement with FMC, DuPont currently has the exclusive marketing rights to sulfentrazone in soybeans. As a result, Authority Broadleaf, Cover, and Authority First/Synchrony STS will no longer be marketed. Authority may be applied preemergence or preplant incorporated at 4 to 5.3 ounces per acre. Do not apply Authority after soybean emergence; severe crop injury can result. In University research, Authority has caused some soybean response from preemergence applications. There is increasing evidence that suggests some soybean varieties may be more sensitive to sulfentrazone than others.


Which glyphosate–type products may be applied postemergence to glyphosate–resistant (Roundup Ready) soybean varieties in 1999? In the past, only Monsanto brand Roundup or Roundup Ultra herbicides could be applied postemergence to Roundup Ready soybeans. There are, however, other options available in 1999. Several agrichemical manufacturers have reached agreements with Monsanto that will allow them to sell their brand of glyphosate–type herbicide for postemergence applications on Roundup Ready soybean varieties. Table 4 lists manufacturers that currently have agreements with Monsanto. Not all these agreements allow for applications of these manufacturers' glyphosate–type herbicides in 1999.--AH, MM

Table 4. Glyphosate-type products for use in Roundup Ready soybeans.

Herbicide manufacturer

Glyphosate-type product

Apply postemergence in Roundup Ready soybeans in



1999 when labeled







Dow AgroSciences



Micro Flo




premixes with glyphosate





Author: Aaron Hager Marshall McGlamery