By Darren Hefty

WHY should you use a pre-emerge herbicide in corn?

Here are some reasons to consider.

  1. MORE YIELD – University and independent studies have shown yield loss in corn for decades when weeds are allowed to grow.  It’s estimated that for every one inch of weed growth in your field, you lose 4.7 bushels per acre.  If you’re waiting to control weeds until they’re four inches tall, you’re losing close to 20 bushels per acre!
  2. CLEANER FIELDS – Controlling Roundup-resistant broadleaf weeds – or really any broadleaf weed, for that matter – in soybeans and other broadleaf crops is not easy.  Wiping them out completely in grass crops like corn is a great way to reduce weed pressure in your field for next year’s crop.
  3. FLEXIBILITY – Using a pre-emerge residual herbicide gives you a much wider window to spray your post-emerge herbicide (see point #1).  Now you’re free to keep planting the rest of your farm instead of stopping to spray the corn before the weeds take over.

WHAT products should you use?

CONVENTIONAL CORN – Use a standard grass herbicide at the full rate.  Products like Harness, Surpass, Dual and Outlook do a very good job on most spring annual grasses like the foxtails.  They also do a nice job controlling many of the small-seeded broadleaves early in the season like lambsquarters and pigweeds.  By wiping out almost all of the grasses, you eliminate the need for expensive post-emerge grass herbicides and save yourself a bunch of money and yield.

HERBICIDE-TOLERANT CORN – If you can spray Roundup or Liberty post-emerge to clean up escape grasses and broadleaves, you have the flexibility to use one of the combination broadleaf/grass herbicides pre-emerge to take two really good shots at problem broadleaf weeds.  There are a lot of products in this market, but here are a few of the big guns.

  • TripleFLEX or SureStart – Both of these products contain a grass herbicide plus Hornet for broadleaf control.  Strengths include pigweed, lambsquarters, velvetleaf and even some cocklebur and sunflower suppression.
  • Balance Flexx and Corvus – Both of these products contain Balance Flexx.  Corvus adds Varro, which stops some grasses and adds broadleaf control for non-ALS resistant weeds.  Strengths include kochia, pigweed, lambsquarters, and ragweed control. 
  • Verdict – Contains Sharpen (Kixor), which has the best burndown activity of the products mentioned here.   It likely comes at a higher price than the other options, but the efficacy is very good.  Strengths include marestail, pigweed, lambsquarters, kochia and ragweed control.
  • Lumax – There are several variations of products that contain Dual and Callisto.  Some of them have atrazine, as well.  Strengths include pigweed, lambsquarters, ragweed and kochia control.  The biggest drawback to Lumax is simply the atrazine.  While atrazine does kill weeds, it can also leach fairly easily into groundwater.  Our advice is to skip the atrazine pre, save it for post, and avoid most of the environmental issues.