Answers are from the Indiana certified crop adviser panel: Betsy Bower, Keystone Cooperative, Lafayette, Ind.; Jeff Nagel, Keystone Cooperative, Lafayette, Ind.; Marty Park, Gutwein Seed Service, Rensselaer, Ind.; and Dan Quinn, Purdue Extension corn specialist.

 

All my seed and retail guys want to talk about is tar spot. Seed dealers want me to switch hybrids. My agronomist is pitching a special scouting service for tar spot at an additional $5 per acre. Is all this hype justified? What should I do to be ready?

 

Bower: Reports from the Crop Protection Network indicate that in the past several years, tar spot has been the No. 1 yield-robbing foliar disease in corn. In 2022, it was responsible for 116 million bushels of yield loss. It was common to see yield losses of 50 to 80 bushels per acre. There are hybrids with more tolerance to tar spot but no corn hybrids that are totally resistant.

 

In 2024, tar spot was found in every county in Indiana, and it was found earlier than ever before. Tar spot can survive for at least two years. Fields can be infected endemically or from rain fronts that bring spores from other areas. Tilling corn residue will not prevent a tar spot infection.

 

Prepay for one fungicide application for your corn acres. If environmental conditions do not support tar spot infections in 2025, you do not have to use the fungicide.

 

Nagel: Tar spot is not hype. Farmers are experiencing how serious yield losses can become from this disease. Yield losses can easily be 20 or more bushels per acre, depending on the hybrid and environmental conditions.

 

All hybrids have some degree of susceptibility. Seed companies are working to bring tolerance/resistance to hybrids. Hybrid selections should be based on yield potential and other agronomic factors, and not tar spot alone. However, have some idea of relative susceptibility of the hybrids you plant.

 

Scouting is important, but it is hard to scale with field scouts qualified to identify early symptoms. If scouts are well trained and directed to areas where tar spot is most likely to develop first, then $5 per acre could be a sound investment.

 

Park: Tar spot has the potential to devastate yield if not managed properly. It continues to be a very unpredictable disease. So, be aware of what is happening in your area and have a plan for it, as it can “sneak up” on you.

 

Spending $5 per acre for scouting might be a wise investment, but scouting can be a challenge. Tar spot can progress rapidly, and you might not be able to react in a timely manner with a fungicide application. Seed companies continue to make improvements on genetic tolerance, but it is a slow process. Most growers in northwest Indiana anticipate this disease coming and have made fungicide application part of their management plan.

 

Quinn: Tar spot can cause yield reductions upward of 50 bushels per acre. So yes, the hype is often justified. But understand that when and where the disease can start becoming a problem is often very challenging to predict.

 

Hybrid selection and scouting are the most effective ways to manage and monitor for the disease. Scouting also can help you make an informed and timely fungicide decision. The field crops pathology program at Purdue tracks every county across the state on tar spot, which can be useful to understand if the disease is close. Also, free apps like TarSpotter can help you understand current risk levels.