Use Case: How Early Tar Spot Detection Turned a Wait-and-See Fungicide Call Into a Targeted Plan

For growers on a two-pass fungicide program, the hardest call of the season is often the second one: spray now, or wait until you see disease? In 2026, one Indiana corn grower answered that question with data from his own fields and treated four of his six fields at V8, well ahead of tar spot.

The situation: a skipped V5 pass and an unusual weather year

This grower did not make a V5 fungicide application this season. His V5 Fungicide Opportunity Report in AGMRI flagged that decision as worth a second look. It showed more than $16,000 in potential return across his fields if he treated the right acres. Tar spot is a recurring concern in his region. Like many two-pass growers, he wanted to wait for visible disease pressure before committing fungicide dollars. But 2026 weather was anything but ordinary, and those are exactly the conditions that can speed disease spread once it takes hold.

The challenge: tar spot is hard to catch early

With higher input prices, blanket fungicide applications can be inefficient. Even with a V5 report showing strong ROI potential, this grower wanted his decision grounded in current disease pressure, not a spreadsheet alone. That is a familiar bind. Tar spot’s first signs are tiny lesions that are easy to miss in the canopy. Once that first lesion shows up, the weather dictates how fast it spreads. In an unusual year, waiting for confirmation can mean acting too late and leaving yield on the table across multiple fields.

The solution: whether, when, and where

Predictive Disease answered whether and when. AGMRI’s Predictive Disease found tar spot in one of his fields about a week after Indiana’s first confirmed case of the season, and before any confirmed case in his county. The field card showed the risk level and a defined action window before disease was visible across the field.

That changed the decision. Instead of waiting for tassel, he made a fungicide pass at V8. It was earlier than usual for him, but clearly warranted by the risk in his own fields. The V5 Fungicide Opportunity Report answered where. His highest-opportunity field, at the top of the report’s ranked list, was the same field where tar spot had turned up. Using that ranking, he treated the top four of his six fields, concentrating the pass on the acres with the most return potential instead of treating everything or guessing.

The results

• $16,000+ in ranked return potential targeted with his fungicide dollars
• 4 of 6 fields treated, prioritized by ROI
• V8 application, ahead of tassel, based on predicted risk

By pairing early detection with field-level ROI ranking, he acted ahead of the disease instead of chasing it, and prioritized the right fields during a busy stretch.

What this means for your 2027 fungicide plan

The grower made the call. AGMRI gave him the field-level evidence to make it with confidence. Looking ahead, he plans to lean on AGMRI to time and target future passes, so the V5 decision is data-backed from the start.