Weed Management Pointers For Grain Sorghum

DR. LARRY STECKEL

JACKSON, TENN.

  It sounds like there is a little more interest in planting grain sorghum this spring compared to more recent years. As such producers who have never planted grain sorghum or have not planted it in years may be trying some this year.  With this in mind here are some pointers on weed management recommendations in grain sorghum.

   1. Choose fields that do not have major infestations of johnsongrass. 

   It is also best to plant grain sorghum in fields that have overall lower annual grass pressure in general. There are some options to control emerged grasses in grain sorghum but they are more limited than what there is in other crops.

   2. Make sure the grain sorghum seed is Concept treated. This will give grain sorghum seedlings protection from herbicides like Dual Magnum, Outlook and Warrant. Seed is typically treated before it goes to the farm, but double check the seed sack to make sure.

   3. Start clean. My “go to” burndown for grain sorghum is 10 ozs of Verdict + 32 ozs of glyphosate. If the field has glyphosate-resistant grass and clethodim is needed, remember to wait 30 days before planting grain sorghum. Another fairly economic option would be paraquat + atrazine.  However, I prefer the Verdict option as it is very flexible in that if the field needs to be switched to soybean it can be without concern of atrazine injury. The Verdict option also provides much better residual grass control than atrazine. Some may want to use glyphosate + dicamba or 2,4-D as the burndown. I shy away from this as under some soil/weather conditions dicamba or 2,4-D can wash down into the slot as grain sorghum is emerging which can reduce crop stand. This is rare as the emergence timing has to line up just wrong with the poor weather and soil conditions, but I have seen it happen.

   4. Use an effective PRE. Some very effective PRE options for grain sorghum include the mesotrione-containing premixes like Lexar, Halex GT, and Coyote. If the field is infested with a lot of annual grasses, premixes containing mesotrione and/or S-metolachlor are preferred. Be aware, mesotrione-containing premixes can only be used PRE in grain sorghum. They will harm grain sorghum if applied POST, and Halex GT will outright kill the crop.  Another good option is Dual II Magnum applied at a minimum of 1.3 pts/A + atrazine.  Verdict at 10 oz/A is another very effective PRE applied option.

   5. Use an effective POST. The “go to” POST applied for most grain sorghum is Dual Magnum + atrazine (premix = Bicep). One can add Huskie to Bicep for help on larger broadleaf weeds like velvetleaf. The best option for emerged annual grasses is to add Facet L to the Bicep.

   6. The last point circles back around to the first one. If a field that is intended for grain sorghum does have a lot of johnsongrass, consider planting Inzen grain sorghum seed. Grain sorghum with this trait is resistant to nicosulfuorn (Zest). ∆

   DR. LARRY STECKEL: Extension Weed Specialist, University of Tennessee