Here we are in later January 2017 and realizing that with good conditions, planting could be something like a little over three months away potentially! I look out at the snow-covered fields around eastern South Dakota, and I can't help but notice that there are a few things still poking above the snow other than crop residue. 2016 was a difficult year for weed control, especially in soybean. That's my topic today- FOUR absolute rules the 2016 really reaffirmed for me in soybean weed control.

Here they are:

  1. You absolutely positively must start the year clean!
  2. Always use a full rate of an effective pre-emergent herbicide.
  3. Keep weed size small- quite small- for post-emergent herbicides.
  4. Be sure to overlay an effective residual herbicide midseason to provide control of late emerging weeds like waterhemp.

I will focus on all of these in the next few blog posts, but let's get started with the first one. 

You absolutely, positively, must start clean. There is absolutely no getting around this hard and fast rule. Starting clean can come from tillage, or more likely from the use of herbicides. Every label for post-emergent use or burndown will have a maximum weed size restriction posted. I don't gamble much, but I would bet any day that a majority of the weeds that were missed last year- with burn down or postemergence in soybeans- were larger than the weed size listed on the label. I used to say if they were smaller than a pop can, weeds would die pretty easily with our first herbicide. So much for easy to remember references! We found pretty clearly this last year that if a burn down was used on the weed over about three inches tall, it became very difficult to control

Here are a few tips:

  • Roundup still is key, but not alone. Use a full quart or more, add a great burndown oil adjuvant like Firezone or Exuro, and apply it with another effective burn down or pre- emergence residual.
  • A stronger burn down stand-alone ingredient like in the Authority line of products, in BroadAxe XC, the higher rates of Valor, or something with Sharpen or Aim all performed well. Mixes that had lesser burndown fell short and made a twisted, and frankly angry weed.
  • "Old school" chemistries like 2,4-D or even dicamba (and dealing with the labeled preplant intervals) really worked well, too.
  • Dicamba tolerant soybeans? That's a whole other blog post.
  • This year another old chemistry may make a nice resurgence. Gramoxone herbicide from Syngenta – a paraquat product- has come down in price significantly this year. Gramoxone still has some handling precautions, but if you can work through those, it can be a very effective non-selective burn down for use in your crops especially if you can apply it with some UAN (and in corn, with atrazine). Gramoxone has no residual and can be used safely ahead of essentially all crops.
  • Tillage certainly had a place, but may not be 100%. Be sure vertical tillage tools, as good as they are, are working and not simply lifting some bigger weeds straight up and dropping them back right in place.
  • Use multiple modes of action in each sprayer pass, and avoid using the same mode of action in burn down, pre-emergence and post-emergence applications, if possible.

So there you have it rule number one for weed control going into 2017 – absolutely positively start the year clean! Do whatever you have to do to get rid of all of the new kochia, marestail, winter mustards, and early grass before you put a seed in the ground. This will get your residual herbicide – the next topic – off and doing the job that it was supposed to do- giving you several weeks of clean fields shortly after planting. Visit with your local wheat growers agronomist that any of our agronomy locations to talk about maximizing your ROI through weed control programs that work. As always be safe and all that you do.