By Brian Hefty

There are a lot of great herbicide choices in almost every crop.  Unfortunately, in soybeans we don’t have as many post-emerge broadleaf options as we need.  If you want to control waterhemp, kochia, ragweed, or marestail post-emerge, good luck.  All of those weeds have Roundup-resistant biotypes that could be in your field.  If you want to be certain of control, which also means higher yield, you need to use a great pre-emerge program.

As soon as I advise a farmer he needs to use three pre-emerge herbicides in soybeans, he immediately says, “I can’t afford that!”  However, did you know that it’s possible to get three pre’s for less than one application of Cobra ($20 per acre for the full rate)?  Here’s the program we recommend:

  1. Metribuzin.  Yup, you can’t use it in all situations, but you can use it in most.  If you have pure sand, skip it.  Otherwise, we typically suggest one-third of a pound per acre for around $4.  If your soil pH is over 7.4, cut the rate, which also saves you money.  Since metribuzin is more active in high soil pHs, you still get good control when reducing the rate.  Metribuzin has contact and residual activity on most broadleaf weeds.  It doesn’t last very long in the soil, so carryover to corn or wheat is no issue.
  2. Valor or Authority.  2 oz. of Valor, after rebate, is around $6, but you can certainly use up to 3 oz. per acre if necessary.  You can’t buy Authority by itself, so you may consider Authority MTZ (Authority plus metribuzin) or Authority First (Authority plus FirstRate).  Valor and Authority, both PPO herbicides, are very good on most broadleaves, but it’s helpful to have other pre’s with them to ensure control, not just suppression.
  3. A yellow.  In conventional-till, you can apply 1.5 pints of trifluralin for about $4 per acre, provided you INSTANTLY incorporate with your tillage tool.  Waiting even an hour to incorporate will sometimes mean significant loss of the herbicide to evaporation.  Sonalan is slightly better, but it is much more expensive.  In no-till, use Prowl.  Prowl does not need to be incorporated.  Like Sonalan, it is approximately 2 to 2.5 times more expensive than trifluralin, but Sonalan and Prowl have less carryover risk to corn and wheat vs. trifluralin.

$4 plus $6 plus $4 = $14.  Even if you are in no-till using Prowl, your cost will likely still be just $20 per acre.  Yes, I said JUST $20 per acre.  At $8 per bushel soybeans, that’s 2.5 bushels.  If you have many weeds at all, it is likely that 5 to 10 bushels per acre could be lost.  I know that you want to cut costs wherever you can this year, and I do on our farm, too.  However, the important thing is to not sacrifice more yield than what you save in costs.

There are a lot of pre-emerge herbicide choices out there, but our advice is to avoid using something pre that can be used post.  For example, Flexstar, FirstRate, and Pursuit are all decent (although not great) post-emerge herbicides in soybeans, but if you use them pre, you can’t/shouldn’t use them post unless you want to plant soybeans again next year.

If you’ve never tried the three pre approach, at least do it on a few acres.  We use this on all our soybean ground, and we typically achieve more than 99 percent control on Roundup-resistant weeds.