The Indiana Certified Crop Adviser panel includes Betsy Bower, Purdue Extension senior research associate, West Lafayette; Abby Horlacher, Nickel Plate Consulting, Sheridan; Brian Mitchem, Farmer 1st Agronomy Consulting Services, Decatur; and Dan Quinn, Purdue Extension corn specialist, West Lafayette. 

 

Last year, I was so focused on scouting for tar spot that I was blindsided by southern rust. Which diseases are shaping up to be most prevalent in corn this year? How often should I be scouting? When do I pull the trigger on a fungicide pass?

 

Bower: Every year is different. Some years, the stars align for infection by tar spot. Last year, we had spores and the right environment for southern rust to explode in some areas of Indiana. 

 

Scout at least once a week starting around V12-V15 for diseases like tar spot and southern rust. You can find signs of other diseases earlier, but V12-V15 allows you to be on top of the foliar diseases that will impact grain fill. Also, you can monitor corn diseases in southern areas with the Crop Protection Network. 

 

Pull the trigger on fungicide if you find a few lesions, if you still have more than a month to complete grain fill and if environmental conditions are right for disease progression. 

 

Horlacher: Tools such as the Tarspotter app and the Crop Protection Network’s Crop Risk Tool can help identify diseases that may be at higher risk in your area. Diseases like southern rust are typically introduced through storm systems rather than overwintering in your soils.

 

Fields with a history of consistent disease pressure should be prioritized for scouting, especially as canopies close and conditions become more favorable for disease development. Scouting should begin about four to seven days after rainfall events while also monitoring disease forecasting tools and local field reports.

 

When planning fungicide applications, review product labels carefully. Some fungicides are most effective when applied preventatively, while others can be applied at the onset of disease symptoms.

 

Mitchem: Last year, southern rust traveled further north in the state than it had in previous years. But that is irrelevant this season because southern rust does not overwinter.

 

Tar spot does overwinter and remains the most impactful disease for most in the state, followed by southern rust in the southern half of the state. Leaf diseases like grey leaf spot and northern corn leaf blight remain present but don’t hurt yield as much as those mentioned previously. 

 

Scouting is a necessity, and fields should be evaluated at least weekly. Pay attention to area reports of infection and adjust scouting accordingly.

 

Fungicides perform best for disease control when applied as a preventative. Be prepared and ready if the environment favors disease development. Yield studies show consistently that if you make one in-crop pass, it’s best applied at the critical protection window when reproduction starts with tassel and ear formation.

 

Quinn: Since the environment often dictates what foliar diseases will be present, it is difficult to predict when and which specific diseases will show up each year. However, southern rust is unique as it can “blow up” from the South depending on the year, so pay attention to pressures in the Southern states and the disease’s movement. 

 

Scout weekly, especially as the corn crop reaches the later vegetative stages and approaches the pollination stage. The most consistent and effective time to make a fungicide pass is at R1 or R2. However, this may shift from year to year based on foliar disease timing and severity. Pay attention to weather as pollination approaches. Is there high precipitation, high humidity, etc.? This may cause high disease prevalence. 

 

Lastly, the Crop Protection Network has a lot of great tools for you to reference to help with disease tracking, prediction and fungicide decision-making.