Virginia Cotton: Burndown Opportunities with Auxin Herbicide Systems

Highboy spraying pre-emerge or burndown herbicide. ©Debra L Ferguson Stock Photography

Our Chemistry or Herbicide choices have not changed significantly; however, there are some new or at least different opportunities that are available in fields that have either Enlist or Xtend technology.  Just keep in mind that what we have been doing still works.

Very uniform planting systems

Just to set the stage, we plant about 98% of our cotton without disturbing the soil prior to planting.  The vast majority of this is strip-till and a few pure no-till operations.  The main challenge of burndown is resistant cool season weeds that have already emerged, and the secondary concern is the warm season weeds that will begin to emerge just before planting or while we are planting the cotton.

Up until This year

While there could be a little bit more diversity here, even last year, our primary burndown strategy has been to burndown in one trip using Roundup + 2,4-D for marestail and primrose + Valor to keep clean until planting.  This had to be done about 3 weeks before planting to allow the 2, 4-D to get out of the system.

The minor altercation of this plant was to split apply the burndown to kill the resistant weeds early with the first trip being 2, 4-D and leave the roundup for later allowing the grass cover to keep growing and getting taller and providing better protection.  Either of these systems remains a viable option, HOWEVER

New Opportunities

  1. 2, 4-D Based – the Enlist system (all Phytogen varieties ending in ‘0’) is approaching half of our acres, and perhaps more with the variety shortages.Enlist varieties have no waiting period required for generic 2, 4-D prior to planting.So it definitely makes more sense to just use one trip and perhaps delay it to get closer to planting and allow the benefit of more cover development.IF YOU CONTINUE TO USE DICAMBA IN AN ENLIST SYSTEM, THEN YOU STILL NEED THE WAITING PERIOD JUST LIKE PREVIOUSLY.
  2. Dicamba Based – the Xtend system (DeltaPine/NexGen/DynaGrow) is also approaching 50% of the acreage. It makes the most sense to switch to dicamba in your burndown. (8 ounces of Dicamba is similar to 1 quart of 2,4-D) Dicamba offers a little better marestail control but weaker primrose control compared to 2,4-D. There is no pre-plant interval prior to planting Xtend varieties when burning down with generic Dicamba. IF YOU CONTINUE TO USE 2, 4-D IN A XTEND SYSTEM, THEN YOU STILL NEED THE WAITING PERIOD JUST LIKE PREVIOUSLY

One Question Remains

If we take advantage of the new herbicide systems and delay burndown to get close to planting, do we still need the Valor?  Keep in mind we want to start clean, so if anything is up that is green, then you need to be sure your preemergence mix is going to kill anything that has emerged.  So if you do not use preemergence, continue using Valor and watch the waiting interval for it.

If you are strip-tilling, there is extremely low risk of injury because the ripper shank moves it out of the way.  7 to 10 days preplant is enough for strip-till.  If you are inside of 7 days, then you don’t need the Valor anyway in my opinion.  For No-Till, there is a rain amount associated with the time of waiting and you generally need to double the time.

How About Planting in Green Cover? (ok – so 2 questions remained)

I have seen this done successfully even before our auxin systems.  And the Auxin herbicides greatly reduce the risk of escape resistant weeds.  Palmer pigweed should be really small if it has even germinated by planting, although watch that ragweed as it can germinate earlier and be larger.  We will get the winter weeds.

So the greatest Risk is the same one it has always been and that is the competition from live cover in sucking the water out of the ground.  It will be drier in the planting zone and I have seen seedling cotton struggle when cover was left after planting.  They say ‘start clean’ for a reason and my recommendation is to ALWAYS burndown before planting as a basic best management rule.

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