Auxin Herbicide Stewardship

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This long, hot and mostly dry spell has made this growing season a real challenge. Hopefully, we will catch a break this week and can get some much-needed general rain across the state. Herbicide drift is even harder for crops to recover from when drought stressed so please remember to use best management practices applying all herbicides but particularly products that contain dicamba and 2,4-D.

There have been several reports of 2,4-D drift issues in Middle Tennessee, mostly the result of pasture sprays. The 2,4-D Amine formulation was very hard to get so some elected to use the 2,4-D Ester formulation in pastures well into June.  The Ester formulation is fine to use when it is cold outside but should not be used in the warmer summer months.  Under hot conditions the ester formulation of 2,4-D can readily get up and move as a gas often long after the sprayer has left the field. The title on the jug “Low Volatile Ester” can be misleading and is referring to the ester formulation being less volatile than older 2,4-D formulations from back in the 1950s.  The amine or choline salt 2,4-D formulations are much less volatile than the older ester formulation and are the safest to use but even they should be used with caution.  Never apply them if a crop downwind is sensitive to 2,4-D.

There have been a few reports of dicamba drift in Middle and West Tennessee. Remember the deadline has come and gone (June 30) to apply Engenia, Tavium and XtendiMax over the top of Xtend soybean.  Liberty is a good alternative to dicamba for Palmer amaranth control in XtendFlex soybean.  In Xtend soybeans the best option would be Ultra Blazer or Cobra. Those two herbicides will likely control some but not all of the pigweed present though.

In cotton, Engenia, Tavium and XtendiMax can still be used over the top of Xtend cotton until July 31.  Please remember that some of the best management practices (BMPs) for dicamba stewardship can be found here at the Tennessee Department of Agriculture’s Dicamba Resources page.

The 2022 Weed Control Manual for Tennessee Field Crops, Forage Crops, Pastures, Farm Ponds and Harvest Aids is in print and posted online. BMPs can also be found in this publication in the comment section for Engenia/XtendiMax/Tavium.

UT data from Dr. Tom Mueller has found that increased air temperature results in increased volatility of dicamba.  Based on this research, Liberty would be a prudent choice to control Palmer amaranth in these hot summer temperatures, especially if there are sensitive crops nearby. Even less expensive and just as an effective option would be to apply herbicides like diuron + MSMA post direct or under a hood.

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