Cover Crop Burndown

DR. LARRY STECKEL

 JACKSON, TENNESSEE

It is cover crop burndown time. There is no one size fits all recommendation for cover crop control.  It really depends on the environment and the cover crop species in the field.  With rain predicted over the next few days, one should be mindful that cover crop burndown can be tricky during periods of saturated soil conditions. This is particularly true with systemic herbicides where translocation of those herbicides to growing points can become limited.

 In general, contact herbicides like Gramoxone or Sharpen mixed with glyphosate can provide more consistent control with many water-stressed 3-plus species cover crop blends.  Another approach is figuring on a sequential application where a glyphosate + dicamba tankmix or Elevore is applied first and then followed in-crop with glyphosate + dicamba in Xtend crops or glyphosate + Enlist One in Enlist crops to remove partially controlled cover crops.

 Dialing in an effective burndown on the 2-species cover crop blend vetch and cereal rye can be more straightforward. Research going back several years showed glyphosate + dicamba providing effective control of cereal and vetch cover blend.  In water-stressed cereal + vetch cover crop some additional measure may be needed to get complete control.  Those studies suggested a sequential application of glyphosate or glyphosate + dicamba applied 7 to 14 days before planting followed by Gramoxone at-planting is an effective control option.

 Glyphosate has at times not been an effective option to control mustards (brassicas) used for cover and 8 to 10 ozs of dicamba mixed with the glyphosate offers little help.  Sometimes poor control of mustards with that mixture is due to environmental stress near application.  Other times the reason for poor control looks to be caused by the mustards turning out to be RR canola.

 The one good cold snap Tennessee was subjected to should have taken out most of the tillage turnips.  That is fortunate as if tillage turnips do not winter kill it is nearly impossible to control them with a herbicide.

 Finally, do residual herbicides work in cover crops?  The short answer is yes most will add a lot to weed control.  Those herbicides that have worked well in cover crops in research would include fomesafen-based herbicides (Reflex, Prefix), the pyroxasulfone-based herbicides (Anthem Maxx, Zidua, Zidua Pro), sulfentrazone-based herbicides (Authority Maxx, Authority Edge, Authority MTZ), flumioxazin-based herbicides (Envive, Fierce, Valor) as well as the encapsulated acetochlor herbicides Warrant and Warrant Ultra.   There are a few that do not work as well in cover crops and they would include Dual and Outlook. ∆

DR. LARRY STECKEL: University of Tennessee