Field Insights

Scout for Tar Spot to Save Corn Bushels

Tar spot escalation has growers asking about disease identification, potential yield loss and fungicide application.

Tar spot was first discovered in Midwest corn fields in 2015 and continues to raise alarm bells. Severe cases of tar spot spread may lead to losses of up to 60 bu/A. Stay ahead of tar spot and prevent significant yield loss by frequently scouting your corn fields and developing a thorough disease management plan. Here’s how:

How to Scout for Tar Spot

Tar spot usually appears as raised, circular black spots on corn leaves, stalks and husks. Some other pathogens have similar symptoms, but the University of Minnesota Extension reports that growers can differentiate tar spot by wetting affected parts of plants and rubbing with their fingers. Unlike other diseases, tar spot will not rub off.

Tar spot has a long latent period, so corn can be infected and begin causing costly damage 14 days or more before you see it in your fields. Start early and scout frequently until silage to stay ahead of the disease and avoid late season losses.

Why Tar Spot Thrives in the Midwest

If tar spot wasn’t a problem last year, it might not be on your radar. However, tar spot thrives in the Midwest climate due to the cooler temperatures and high relative humidity. Increased potential rainfall can increase disease severity and lead to substantial yield loss if you’re unprepared.

To complicate matters further, tar spot overwinters and has spread rapidly since 2015. If tar spot was confirmed in neighboring states or counties, be on guard this year. Pay attention to the forecast and be prepared to pivot depending on tar spot pressure.

What to Know About Potential Yield Loss

Yield loss of 30 to 40 bu/A is common and can be even greater when corn is infected early in the season. But don’t let your guard down later in the season either — even at full-dent, tar spot can cause losses of up to 20%.

Tar spot can have long-term implications as well. Although only 20 to 25% of overwintering spores will survive, even just a few spores can cause significant damage. Under the right conditions, tar spot can produce millions of spores.

How to Manage Tar Spot

It’s tempting to save on input costs, but the possible damage and potential yield loss from tar spot isn’t worth it. Trials show that preventive fungicide applications are significantly more effective than curative applications against tar spot.

Tar spot isn’t the only threat to your corn crops. Other yield-robbing diseases like Northern corn leaf blight and gray leaf spot continue to threaten crops. Prioritize protecting your yields and ROI from a variety of corn diseases with a broad-spectrum plant-health fungicide like Miravis® Neo and Trivapro®.

Long-lasting disease protection is key to managing tar spot. Miravis Neo and Trivapro contain ADEPIDYN® and SOLATENOL® technology for powerful and more long-lasting protection against disease and environmental stress.

April 2024 | by syngenta thrive
  • Tar spot is identified by raised, circular black spots on the leaves, stem and husks.
  • Frequent scouting all season long is key to staying ahead of tar spot and preventing late-season losses. Hear more about it.
  • Timely applications of Miravis® Neo and Trivapro® fungicides help growers control tar spot and preserve yields.