Common Herbicides Used In Soybean That Could Carryover Into Grain Sorghum

DR. LARRY STECKEL

JACKSON, TENN.
   I have written a couple of pieces on fomesafen carryover into grain sorghum. I emphasized fomesafen because it is used on almost all soybean acres in Tennessee. However, I would be remiss if I did not add that some other herbicides commonly used in soybean have lengthy plant backs to grain sorghum as well.
   The Authority (sulfentrazone) containing products like Authority First has a 12 month (12M) plant back to grain sorghum. Other Authority containing products like Authority XL 10M and Authority MTZ which is 12M for 20 ozs/A or less and 18M for rates above 20 oz/A could also be an issue this spring in grain sorghum. Grain sorghum suffering from Authority carryover would emerge fine. However, shortly after emergence the stand would likely die back.
   Herbicides that contain the active ingredient in Classic (chlorimuron) also have some lengthy plant back time before grain sorghum can be planted.  Classic at rates typically used POST in soybean have a 9M plant back to grain sorghum. There are many premixes that contain this herbicide. They include Canopy EX 10M, Envive 10M, Enlite 9M and Valor XLT 10M. Another common ALS-inhibiting herbicide, FirstRate, has a 9M plant back to grain sorghum. Grain sorghum suffering from carryover of a ALS-inhibiting herbicide would not suffer stand loss but would be stunted with purple colored leaf veins.
   We could get into situations where one of the above herbicide premixes was applied PRE in June and then followed with a fomesafen containing herbicide POST. If grain sorghum was planted in late-April we could have two if not three different herbicides causing the milo to have issues on stand establishment. Good record keeping on what herbicide was applied and when last spring should be a deciding factor on which field should be planted to grain sorghum this spring and when it should be planted. ∆
   DR. LARRY STECKEL: Extension Weed Specialist, University of Tennessee