Answers are from the Indiana certified crop adviser panel: Betsy Bower, Purdue Extension senior research associate, West Lafayette; Abby Horlacher, Nickel Plate Consulting, Frankfort; Brian Mitchem, Farmer 1st Agronomy Consulting Services, Decatur; and Dan Quinn, Purdue Extension corn specialist.

 

We did not spray one farm with fungicide last year because we don’t have a dryer at that distant farm, and we didn’t want wet corn. Tar spot killed us. Should we just spray no matter what?

 

Bower: I am not ready to say just spray. Last year, there were several areas in Indiana where tar spot was a non-issue even though it had been previously. And there were areas of Indiana that had not seen heavy tar spot infections before that experienced yield hits from tar spot.

 

Pay attention to where tar spot is found. Purdue Extension plant pathologist Darcy Telenko will keep Indiana updated on tar spot. Her team will check fields for tar spot infection and development. Know your fields hard hit in the past, and scout them first if infections are reported in your area. Scout for tar spot every five to seven days. You can get good protection from fungicides after finding just a few spots.

 

Horlacher: If economic loss from tar spot was greater than the cost of hauling corn to the elevator for drying or waiting until it dried, applying a fungicide would have clearly been the right decision. That said, just because tar spot caused a financial hit last year doesn’t mean it will in future seasons. Record the level of tar spot damage and timing to guide scouting.

 

If tar spot shows up at the same time and in the same way, protect the crop with a fungicide. But if it appears later in the season or stays below the ear leaf, set up fungicide trials to evaluate whether a treatment makes financial sense based on how the disease develops.

 

Mitchem: Tar spot management starts with hybrid susceptibility. We must meet all three corners of the disease triangle for the disease to impact a crop – disease presence, susceptible host and suitable environment. The environmental piece is the key variable.

 

Tar spot will typically start in the lower canopy and rapidly move up the plant if the environment is conducive. If you start observing raised black spots on or near the ear leaf at V12 to V14, schedule a fungicide application.

 

The issue of harvest moisture brings up a management opportunity. With warm weather extending our growing season by 400 growing degree units as compared to 25 years ago, harvest moisture has become less of a concern if we plant similar maturity hybrids. Controlling tar spot is the priority.

 

Quinn: Scout and use available prediction tools to understand when risk for infection is high and when the disease is found. This new tool from the Crop Protection Network shows risk potential for the disease at your location.

 

Also, scouting will be important to make an informed fungicide decision. If the disease comes in early, spray at R1 or R2. This typically provides the most consistent response when disease severity is yield-limiting. However, if the disease is in your area but doesn’t infect your plants until R5 or later, then the fungicide application will not be worth it, and the disease will likely not be yield-limiting.