Tips for Managing Tar Spot Disease in Corn

Tar Spot devastates corn yields or is just a cosmetic issue, depending on when the infection occurs and a hybrid’s overall health. The wide differences of infection from year to year make it difficult to identify genetic backgrounds that we can call “tolerant” with a high level of confidence.

Hybrids become infected for many reasons, including pressure from leaf diseases like Rust, Northern Corn Leaf Blight or Gray Leaf Spot. Hybrids with decreased overall plant health due to an imbalanced fertility program also show potential for severe infection. The key to protecting plants from Tar Spot infection is to manage fields to create the best plant health.

As we prepare for the next growing season, keep in mind that:

  • Infection rates vary from year to year.
  • Continuous corn acres are more susceptible.
  • Hybrids with marginal late-season plant health can be more susceptible.
  • Imbalanced soil fertility that reduces plant health can play a role.

Lyle TT

These management techniques can minimize infection rates:

  • Manage fertility within the field. Although nitrogen (N) plays a major role in creating yield, remember to balance potassium (P) and phosphorus (K) levels. Proper P and K levels maintain root and stalk health later in the season to lessen effects of infection.
  • Be proactive with your fungicide application program. Fungicides today protect plants from disease and make them more efficient in translocating water and nutrients. Multiple fungicide treatments during a season offer opportunity to maintain plant health. Plan for it rather than being reactive.
  • Select hybrids with the best late-season health ratings. Consider planting hybrids with a slightly later maturity – up to four days or more later than your normal maturity – to maintain health later into the season.
  • Move to a corn-soybean rotation. If this rotation is not an option, follow the tips above to maintain plant health.
  • Planting process can be key. Uniform emergence optimizes plant health throughout the growing season. That’s why uniform planting depth is so important. Be sure to plant deep for optimal root crown development. Finally, soils temps and soil conditions at planting time also contribute to uniform emergence.

Our experience has shown we can rate a hybrid a “2”, using a 1 to 5 scale where 1 is best, one year. The next year it might be rated a “5” the next year.  We can even see rating differences during the same season, depending on field management.

Putting together a plan that creates the best overall plant health is your best tool to defend your crop from Tar Spot infection. Start building your plan now. Remember to execute the entire plan next season, beginning at planting time. Crop planning equals success!