By Brian Hefty

Tens of millions of soybean acres in the U.S. are switching this year from Roundup beans to either Xtend or LibertyLink soybeans due to weed resistance.  How does that change your pre-emerge herbicide selection?  Which pre’s should you use if you are staying with Roundup beans for one more year?

Most importantly, no matter which trait you use we strongly encourage you not to skip the pre.  The trait companies are heavily subsidizing pre-emerge herbicides because they know, too, that their trait can only hold out so long if farmers use just one mode of action time and time again.  That’s what killed straight Roundup beans, and they are hoping not to see that again.

IF YOU STILL PLANT ROUNDUP SOYBEANS, HERE IS OUR RECOMMENDATION:

Without question, you need 3 pre-emerge modes of action because there are no perfect rescue options if Roundup no longer works, especially when we’re talking about kochia, marestail, and even Palmer pigweed and waterhemp.

  • PPO – Pick either Authority or Valor here.  While Sharpen is a PPO and offers nice burndown, soybeans are very sensitive to Sharpen.  You must use a low rate of Sharpen because of this, which means there is not enough residual.  Authority and Valor are both very good on small-seeded broadleaves, and they have a little activity on grass.  They can be used in almost any soil type or soil pH, and they are inexpensive.
  • Metribuzin – Speaking of inexpensive, the price of generic metribuzin (this is the active ingredient found in the old Sencor herbicide) keeps coming down more every year.  The full rate for soybeans in most areas is two-thirds of a pound, but to be safe, we typically only talk about one-third of a pound.  In higher pH soil, many farmers use one-sixth of a pound with great success.  Either way, you invest only $2 to $4 per acre, and you get good activity on lambsquarters, kochia, waterhemp, Palmer pigweed, ragweed, and many other broadleaf weeds, along with slight grass suppression.  Like Valor and Authority, metribuzin has some burndown activity, but metribuzin doesn’t have as much residual, especially when you get lots of rain.
  • Yellow – Sonalan, Trifluralin, and Prowl are all excellent grass herbicides, but they have decent suppression on many small-seeded broadleaves, as well.  Sonalan and Trifluralin must be instantly incorporated, leaving Prowl as the only yellow that fits in no-till.

Our advice is to mix all 3 of these herbicide categories together and either lightly incorporate or leave them on the soil surface prior to soybean emergence.  I know 3 pre’s sounds expensive, but your cost is just one to two bushels of soybeans.  If you have almost any weeds in your field, you’ll likely give up more than one or two bushels.

FOR XTEND OR LIBERTYLINK SOYBEANS:

There really isn’t much difference here, as we would still love to see you use 3 pre’s.  I know we will on our farm.  However, if you have low weed pressure you can probably get by with just two of the three.  Definitely keep the PPO (Valor or Authority), and then use either metribuzin or a yellow as your second component.

ARE THERE ANY OTHER OPTIONS?

There are lots of options, but we feel these products provide the best value (lowest cost plus best weed control) in most situations.  Here are some other herbicides that can be used, but we usually don’t recommend them.  Also, I’m listing straight products here.  There are many premixes that contain these individual herbicides, and premixes are usually cheaper.

  • FirstRate – We prefer to see you save this for post-emerge in straight Roundup beans, but for Xtend and Liberty beans FirstRate gives you nice suppression on ragweed.  Since it is an ALS herbicide, it won’t help you on any of the ALS-resistant weeds, though.
  • Pursuit – We would rather see 2 or 3 ounces at the most instead of the full rate of 4 ounces per acre to reduce carryover potential in areas where this is a concern.  Pursuit even at a half rate is excellent on nightshade, and it has good activity on wild buckwheat and many other non-ALS-resistant weeds.
  • Flexstar – Here again, we like this better post-emerge in straight Roundup beans because Flexstar can control small pigweeds.  Flexstar has a long residual, so do not exceed the labeled rate, and don’t use it twice per season.
  • Group 15 Herbicides – This includes Dual, Outlook, and Zidua.  I don’t want you to get too carried away on this chemical family in soybeans because we need it in corn.  While many people are touting the activity that Group 15 herbicides have on small-seeded broadleaves, our experience has shown these Group 15s are way weaker than the yellows, PPOs, or metribuzin.  Where the Group 15s have the best fit is early post if you need to extend your residual.  For a pre choice, use something else instead.