Tar Spot is on our radar as a key disease to be mindful of for the 2024 growing season. A few key points to consider:

  • It’s a relatively new fungal disease to the U.S. that infects corn leaves.
  • It’s capable of reducing corn yields by as much as 60%.
  • Crop standability can be significantly impacted, making harvest more difficult, costly and inefficient.
  • It can also reduce silage quality and quantity.
  • The fungus can overwinter in infested crop debris.
  • Spores can travel long distances.
  • Moderate temperatures, cloudy conditions and extended periods of leaf moisture are ideal conditions for the disease to persist.

What To Look For

Small, black raised spots (circular or oval) develop on infected plants, and may appear on one or both sides of the leaves, leaf sheaths, and husks. Spots may be found on both healthy (green) and dying (brown) tissue. Often, black spots are surrounded by a tan or brown halo. Source: Purdue University, Darcy Telenko.

 4 Tips to Protect Yield From Tar Spot

  1. Apply a premium fungicide at VT/R1. If you’re only going to treat the field once, we recommend the VT/R1 timing and using a top tier fungicide like Miravis Neo, Veltyma or Delaro Complete. A second application may be necessary. If it is, a premium fungicide is an option, but many times a good combination of triazole and strobilurin chemistry like Rustease or Protegam YLD can provide good additional control.
  2. Disease symptoms don’t always correlate to yield response. Due to the makeup of the tar spot pathogen, the correlation between yield and tar spot severity doesn’t always exist. If you’re evaluating trial data, focus on yield results more than subjective disease ratings to get the best idea of how products will perform against the disease.
  3. Avoid tar spot tunnel vision. While tar spot is top of mind, it’s important to remember that we need to control other yield robbing diseases like Northern Corn Leaf Blight and Gray Leaf Spot.
  4. Use a longer lasting fungicide. Many of the newer three mode of action fungicides provide longer periods of control than the older two mode of action fungicides. These newer products that contain SDHI chemistry can provide targeted control for longer periods of time.

Build Your Disease Management Plan Today

Work with your local Mercer Landmark Crop Production Advisor to be sure your fields have a fungicide application in the plan. If you’re planning on aerial application, now is the best time to book those applications, so the availability of airplanes is greater for our area. In addition to securing the availability of a plane, an early commitment leads to better pricing for both the application and the products themselves.

Information sourced from printed materials provided by Bayer and Syngenta.