By Darren Hefty

You’ve gotten the crop in (or you’re nearing completion) and so far have made the fertility choices and weed control decisions necessary for a high-yielding crop.  Is now the time to starting cutting costs? The next major input investment coming up is whether or not you think disease and stress could cost you yield this season. Your main protection option at this point is spraying a foliar fungicide on corn in the V4 to V7 stage (4 to 7 fully developed leaf collars), but will it pay you a nice return on investment (ROI)?

The cost of fungicides has come down, PLUS at the V4 to V7 timing you will often be using a lower fungicide rate than when the corn crop is fully grown (VT-R1).  The result is a cost for the top of the line fungicide products in the $3 to $8 per acre range (minus any applicable rebates and programs).  Add to that the fact that at V4 to V7 you may already be spraying the field yourself with a herbicide and could add the fungicide to it without requiring a separate application.

In order to justify the application, you need to see at least a 2:1 return.  If it costs roughly $3/acre for the least expensive fungicide, it needs to pay you back at least $6/acre, or about 2 bushels.  Here are 10 factors that could lead to a higher return for you.

  • Continuous Corn
  • Racehorse Hybrid
  • History of Disease Issues
  • Reduced Tillage
  • Average to Above Average Precipitation
  • Disease Present in Areas Upwind (South) from You
  • High Yield Potential
  • Stressful Growing Conditions
  • Insect Feeding
  • High Plant Population and/or Narrow Rows

The more of these factors you have working against you, the higher the likelihood of a nice gain using a foliar fungicide at this stage of the season.  Also, for fungicides to work their best, you need to understand:

  1. Fungicides work primarily in a preventative mode before disease is present.
  2. Fungicides work best with great spray coverage, meaning smaller droplets – NOT ROUNDUP TIPS!
  3. Fungicides protect only leaves they cover well. When new leaves emerge they are unprotected.
  4. Fungicides often last 2 to 3 weeks at best, so re-treatment later may be necessary.