Phaeosphaeria Leaf Spot Confirmed in Michigan Corn

The fungal disease has spread across 20 Michigan counties, impacting cornfields throughout the state.

Updated on Oct. 9, 2026 in Botany

Phaeosphaeria Leaf Spot Confirmed in Michigan Corn

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Phaeosphaeria leaf spot has been confirmed in approximately 20 Michigan counties, marking a significant expansion of the fungal disease. Cases have also been identified in New York, with additional suspected infections in Pennsylvania and northern Indiana.

Why it matters

The spread of this disease presents a new agricultural challenge as symptoms often resemble other conditions like paraquat herbicide injury or holcus spot. With no fungicides currently labeled for treatment, researchers are racing to identify management strategies.

Researchers have confirmed the presence of the disease with 95% confidence through fungal isolation and greenhouse symptom verification. This follows historical precedents of severe tar spot epidemics that caused yield losses of up to 50%.

The details

Researchers are currently isolating the fungus from diseased tissue and reintroducing it to healthy plants in greenhouse conditions to verify symptoms. While agricultural companies are exploring emergency exemption labels for fungicides, no chemical treatments are currently authorized.

1999: The disease was first reported in Florida seed production.
2016: Tar spot was first discovered in Allegan County, Michigan.
2018: Severe tar spot epidemics caused significant yield losses.
2021: Another severe tar spot epidemic occurred in affected fields.
October 2026: Phaeosphaeria leaf spot spread was confirmed across Michigan.

The Big Picture

The emergence of Phaeosphaeria leaf spot follows the destructive path set by the 2018 and 2021 tar spot epidemics. This discovery shifts the research focus toward screening corn hybrids for resistance and validating fungicide efficacy against a new, poorly understood fungal threat.

Local farmers and agronomists may need to adjust monitoring protocols as the disease mimics common herbicide injuries. Future management will rely on the successful development of resistant corn hybrids or the approval of emergency fungicide labels.

The takeaway

Growers should differentiate between this new spot and existing herbicide injuries to ensure proper crop management. Researchers are prioritizing the identification of resistant hybrids to mitigate potential long-term yield impacts.