Tar spot has been confirmed in North Carolina corn for the first time, according to Successful Farming, extending the reach of a foliar disease that has cut Midwest yields by tens of bushels per acre in untreated fields since its U.S. arrival in Illinois and Indiana in 2015.

The detection ends North Carolina's run as one of the few Southeastern corn states without a recorded case of the pathogen Phyllachora maydis. It places crop advisors, extension specialists and corn producers on alert as the season progresses, and reshapes the case for in-season fungicide investment on corn acres that have historically run lighter spray programmes.

What does the North Carolina detection change?

Tar spot presents as raised, black, tar-like stromata scattered across corn leaves, husks and stalks. The pathogen overwinters in crop residue and spreads by wind-dispersed ascospores that can travel miles in a single weather system. That combination makes containment almost impossible once the disease takes hold in a region.

University research from across the Midwest has documented yield losses of 20 to 50 bushels per acre in severely affected, untreated fields, with the worst cases exceeding 60 bushels. The disease thrives in moderate temperatures of 60–70°F and extended leaf wetness — conditions that recur across much of the eastern United States in mid-to-late summer, including the Coastal Plain and Piedmont regions of North Carolina.

Since the first U.S. detection in Illinois and Indiana in 2015, tar spot has reached more than 20 states. Iowa, Illinois, Wisconsin, Michigan, Minnesota and Indiana have carried the heaviest cumulative losses. The pathogen has steadily pushed into Ohio, Pennsylvania, New York and Ontario — and North Carolina is now the latest step in that eastern and southern drift.

What should North Carolina growers do now?

The first operational decision is scouting intensity. Midwest experience shows tar spot often appears first in fields with the heaviest residue, lowest airflow and most consistent dew — the same fields most growers already walk last.

Growers should prioritise the following moves:

• In-season walks in irrigated corn and continuous-corn fields, where residue and humidity favour infection
• Fungicide timing at VT/R1 through R3, using strobilurin-plus-triazole or SDHI-containing products that have shown consistent efficacy in university trials
• A budgeted $15 to $30 per acre for a single aerial or ground pass, with a second application justified in high-risk fields
• Residue management planning for the following season to reduce overwintering inoculum

The economics also shift. University return-on-investment studies from the Midwest have shown that a well-timed fungicide pass pays for itself in most years once tar spot is confirmed in a county. In states where the disease is rare or absent, that math rarely works.

Industry estimates put the breakeven yield response at roughly 4 to 7 bushels per acre for a $20 application — a threshold Midwest trials have cleared in most confirmed-presence counties.

North Carolina growers now have one season of confirmed presence to recalibrate their cost-benefit expectations before the 2025 spray decisions are made.

What should growers watch next?

Three pieces of information will determine how the 2024 and 2025 seasons unfold: the county of the initial find, the growth stage at detection, and any subsequent reports within a 50-mile radius. A second confirmation this season would justify a more aggressive fungicide stance statewide in 2025.

Until extension releases more detail, the prudent move for North Carolina growers is to scout early, prepare a fungicide plan, and watch for state and regional updates from N.C. State Extension and the USDA.