By Brian Hefty

Roundup-resistant weeds are here, but that doesn’t mean your weed control or your yields need to suffer.  Perhaps the most important thing you need to do to prevent these tough weeds from damaging your next crop is use a pre-emerge herbicide, and that product could even be applied this fall.

If you want to use a fall residual herbicide AND get good effectiveness out of it next spring, here are my top 5 pieces of advice:

  1. If you spray a soybean herbicide this fall, you have to make sure you are definitely planting soybeans in that field next year OR use a herbicide that can be sprayed on whatever crop you might plant.  For example, if you wanted to apply Prowl this fall, that’s going to be good if you change your mind and want to grow corn next year, but products like Valor and Fierce would be great either way.
  2. Spray late in the season, but not too late.  Ideally, we want soil temperatures cold (less than 50° F), but we do not want the ground frozen solid.  By having soil temps cold, little herbicide will be used up until next spring, meaning you’ll get longer residual next year.  However, if the ground is frozen, it is possible some of your herbicide can wash off with rain or snowmelt in the future.
  3. Plant your crop early in any fields that were fall-applied.  Never forget that crop canopy is an even better weed-killer than herbicides.  If you can get your crop up and shading the rows quickly, your herbicide residual doesn’t need to last as long.
  4. Increase the rate when spraying in the fall.  Yes, this will cost you a little bit more money, but in many cases it is worth it because you should get much better control of winter annuals spraying now, and you will get control earlier in the spring because the herbicide will already be in the field.  In our operation, for example, instead of using 2 or 2.5 oz. of Valor like we have commonly done in the spring, we would apply 3 oz. of Valor in the fall.  As a side note here, any fall-purchased product does qualify for next spring’s rebate programs.  Valor and Fierce qualify for rebates with name brand Roundup, for example.
  5. Consider getting some burndown activity plus residual control out of your fall herbicide.  When spraying late in the fall, the top growth on your weeds may be gone or mostly gone; but that is not always the case.  If you have some winter annuals, why not burn them down as long as you are out there?  Roundup late in the season is not very effective, but Valor, Fierce, and the Authority products should all have contact activity on most annual weeds still present in your fields.  You may also consider herbicides like Banvel or 2,4-D depending on the rate and the crop you want to plant next spring.  Going into corn next year, we often apply 1 quart of Banvel in the fall to completely wipe out marestail, dandelions, winter annuals, and almost any other broadleaves still growing in the fields late in the fall.

You’ll notice I mentioned Fierce a few times in this article.  I have had a lot of questions about that product since it is new, so let me just say that we have many good pre-emerge options in soybeans, but Fierce is among the best.  Fierce contains Valor and Zidua.  Valor is a PPO, and Zidua is from the same chemical family as Harness and Outlook.  Having 2 different sites of action is great, and results with Fierce so far have been excellent.

Whether you spray this fall or next spring, we strongly encourage you to use one or more pre-emerge herbicides to help prevent Roundup-resistant weed issues on your farm.  We invite you to join us at a free Ag PhD Winter Workshop in January or February, as we will give you more detailed information on all your pre and post options to stop tough weeds.