Answers are from the Indiana certified crop adviser panel: Danny Greene, Greene Crop Consulting, Franklin; Bryan Overstreet, soil conservation coordinator, Rensselaer; Dan Quinn, Purdue Extension corn specialist; and Dan Ritter, Dairyland Seed agronomist, Plymouth.

 

I opted to skip the fungicide application in corn this year because tar spot was not a problem last year. However, I found infection in some of my fields in the later reproductive stages this year and still decided not to spray. Now, I am afraid I might be taking a yield hit. What should I do differently next year?

 

Greene: Tar spot is unpredictable, so prevention and quick reaction are key. Scout weekly from tassel through dent. This is the critical window for disease development. If symptoms appear, apply fungicide promptly to limit spread. Another approach is a planned spray in early reproductive stages, with a second application if disease pressure and weather favor continued infection. Avoid vegetative stage fungicide applications for tar spot alone. They won’t provide enough protection later. Also, manage other foliar diseases like gray leaf spot, since stressed plants are more vulnerable to tar spot.

 

Overstreet: First, consider your corn hybrid selection for next year. Several of the hybrids have more tolerance to tar spot than others. Select the hybrids that fit your farming practices and have good tolerance to tar spot. Second, and most importantly, scout early and often for tar spot. The sightings of this disease have been earlier in the season the last few years, so keep ahead of it by scouting. The most economical time to spray for has been at or just after tasseling. But as you saw this year, it can come in later and do some damage. So, keep scouting for it after tasseling.

 

Quinn: The main thing to watch for moving forward is at what specific reproductive growth stage the tar spot is present. If tar spot is present in the lower canopy and at the R5 growth stage or later, then it is often too late to see any yield benefit with a fungicide application. However, if tar spot is present at the R4 growth stage or sooner and is progressing up the canopy, then it is still warranted to make a fungicide application, and a yield benefit will still be highly likely.

 

Ritter: The unfortunate issue with many agronomic concerns is that each year is different. You could manage everything the exact same and not have yield issues the following year. However, weather conditions strongly dictate the prevalence of disease infestation. It is one of the critical sides of the infamous “disease triangle,” along with a susceptible host and a pathogen.

 

Hybrid selection can help you manage this in the future. Sit down with your trusted seed supplier and choose the best disease package available. Although it is difficult to predict the weather, keep an eye on the forecast. Continue to scout fields diligently. Follow up once a week to check corn development and disease progression. If disease infection is outpacing corn development, and the corn is still in a phase that will benefit from an application, consider treating.

 

Some people will simply budget a planned fungicide application as part of the cropping system. Some years it will pay, and in low-pressure years, it may not. This is why scouting is still the gold standard. In a year like this one, it can save you some yield.