By Brian Hefty

Your decisions today could impact the next crop you raise, and possibly even the crop after that.  I love herbicides… IF they control my weeds without injuring my next crop.  Let’s talk about how to avoid the bad, but achieve the good.

  1. Always check the label and talk to your agronomist about carryover potential.  This gets to be more of an issue when you raise a crop outside of the ones commonly grown in your area.  For example, where we farm it is almost all corn and soybeans.  If I want to plant some wheat or some other crop, it’s not exactly top of mind to be thinking about next year’s rotation including anything other than corn or soybeans, but if you don’t plan ahead, your next crop could be hurt.
  2. Get automatic shutoffs for your sprayer.  On our farm, for example, we have a lot of point rows.  Before automatic shutoffs, we damaged a lot of crop, because we would get 2 to 3 times as much product on as we should in those areas.  Not only do automatic shutoffs save your crop, they also save you money when spraying, because every overapplication is more money wasted.
  3. Use some common sense for your area, your weather, and your soil conditions.  Herbicides are more likely to break down when it is hot, wet, in a long growing season, and when soil conditions are normal (neutral pH, low salt, etc.).  If you are farming in western North Dakota where there is less heat, less rain, and if your field has high pH and high salt, guess what?  Herbicides aren’t going to break down as quickly.  In other words, use long-residual herbicides at lower rates or avoid them if you need to rotate to sensitive crops.  While the label gives you guidance on when you can safely rotate to other crops, that’s assuming normal heat, rain, and soil conditions.  Again, please use common sense.

Below are some of the herbicides I’m concerned about when it comes to rotational restrictions.  This doesn’t mean you shouldn’t use these herbicides, but it does mean you need to use the right rate, the right timing, and follow labeled instructions.  By the way, many of these herbicides are found in other tankmixes, so those tankmixes should be watched closely, as well.

  • Flexstar – Due to carryover concerns, the full rate of Flexstar varies from area to area.  For much of South Dakota, for example, a farmer can only use 12 ounces per acre, and the rotational restriction to corn is 10 months.  That means if you want to plant April 15 next year, spraying Flexstar after June 15 this year is out.
  • Classic – When the soil pH gets into the upper 7’s and especially into the 8’s, Classic lasts a long time in the soil.  It can be lethal to next year’s corn in those situations.
  • FirstRate – My fear here has to do with how some people think it’s okay to spray FirstRate pre and come back with it again post-emerge.  It may be labeled, but I feel it’s too risky, especially in high pH soil.  Also, since FirstRate is an ALS herbicide, and we know weeds can quickly develop ALS resistance, I’d avoid spraying it twice in a season.
  • Atrazine – Atrazine is more persistent in high pH soil, but it can be a problem anytime you rotate to a crop other than corn or sorghum.  If you want to go to soybeans, we suggest no more than a half-pound per acre this year.  If you want to rotate to any other crop, I’d skip the atrazine entirely.
  • Any HPPD (Callisto, Bellum, Laudis, Impact, etc.) – The key here is to avoid overlaps and second applications.  I’ve personally only seen visible carryover to soybeans once on our farm, but once was enough.  Years ago, before we had our current sprayer, an overlap from the year before showed up as white soybeans.  Fortunately it was a small area, but it just showed me we didn’t have a lot of margin for error that year, which was extremely dry.
  • WideMatch – Normally this is no concern, but if you want to raise chickpeas, lentils, or potatoes, you should know that WideMatch has an 18-month restriction.  I have seen a problem only one time rotating to soybeans, but that was where manure had been WAY overapplied, so my guess is it was a high salt area, meaning the bacteria that help break down herbicides had died.
  • Peak & Ally – These are very long-lasting herbicides, which is why I never recommend them in a crop field.  If you have one of these two herbicides in your wheat mix this year, you’d better look at the label again because it will be a while before you can rotate to certain crops.

Each year I get calls from company reps upset about something I’ve told you.  I expect to get several calls about this article because my advice will always be more conservative than what the label says.  That’s based on a lifetime of experience, and years of experience with the specific products I’ve listed above.  I’m not after the 99% of the time things go perfectly.  I’m trying to help you avoid the 1% of times when things go wrong.  That’s when people lose money, their sanity, and sometimes even their farms.  I want you to apply residual herbicides often, but cautiously, and always use common sense.