Postemergence options for soybeans

Given the late growing season, many soybeans have not yet been treated with planned postemergence herbicides. Soil-applied herbicides are beginning to fail and weeds are emerging in these fields.

If weed escapes are the major concern, we suggest mechanical strategies be used rather than a postemergence herbicide. If you had planned to apply a postemergence herbicide, carefully consider the stage of soybean development, condition of the crop, and level of weed infestation. Again, mechanical control strategies may be your best option.

The relative risk of herbicide injury to the soybean plant also is affected by the choice of adjuvant. This risk, from greatest potential for injury to least, is COC > MSO > NIS > UAN > AMS. It is important to remember that the adjuvant alone does not typically cause injury, but affects the efficacy of the herbicide. Refer to the herbicide label to determine which adjuvants are labeled and if there is concern for injury, select the adjuvant with the least potential to enhance herbicide injury. Information concerning adjuvant selection is included in the table that accompanies this article.

Another consideration is the legal delay between herbicide application and harvest. Although planting was significantly late this year, harvest could occur around the first or second week in October in "normal" conditions. This is approximately 70 days. However, if an early frost occurs, this number could change considerably. The maximum stage of soybean development allowed for postemergence application is listed in the table below.




Postemergence herbicide options for soybeans.

HERBICIDE MAXIMUM SOYBEAN STAGE ADJUVANTS
Grass control
Assure II Before pod set COC or NIS
Fusilade DX Prior to bloom COC or NIS+\- N(1)
Fusion Prior to bloom COC or NIS +\- N
Poast Plus 80 DBH(2) Dash HC or COC +\- N
Prestige 80 DBH Dash HC or COC +\- N
Select 60 DBH COC +\- N
Broadleaf control
Basagran No restriction COC or N
Blazer 50 DBH NIS or N
Classic 60 DBH COC or NIS +\- N
Cobra 90 DBH COC, NIS, or N
Concert 60 DBH COC or NIS +\- N
Flexstar Prior to bloom COC or NIS +\- N
Galaxy 50 DBH COC or N
Pinnacle 60 DBH COC or NIS +\- N
Pursuit Prior to bloom COC, MSO, or NIS +\- N
Reflex Prior to bloom COC or NIS +\- N
Resource 80 DBH(3) COC
Scepter 90 DBH COC
Stellar 90 DBH COC
Storm 50 DBH COC or N



Notes: 1) N refers to both AMS and liquid nitrogen solutions. Refer to the label to determine which is recommended. 2) DBH = days before harvest. 3) Do not apply after pod set.

This article originally appeared on pages 131-132 of the IC-476(18) -- July 15, 1996 issue.

Updated 07/14/1996 - 1:00pm