East Lansing, Michigan: A fungal leaf spot disease resembling maize white spot has been detected in corn crops across approximately 14 Michigan counties during the 2026 growing season, prompting Michigan State University (MSU) researchers to urgently request plant samples from growers to identify the causal organism. Additional reports of similar symptoms have also emerged from New York and Pennsylvania .
Symptoms and Uncertainty
The disease presents symptoms that closely resemble paraquat herbicide injury, with small pale green spots that later become bleached and necrotic, surrounded by dark brown margins . In affected fields, researchers have observed “notable incidence and severity” .
However, a critical caveat remains: scientists have not yet confirmed the exact fungal species responsible. While historical literature associates the disease with Phaeosphaeria maydis, the taxonomy of that organism remains unresolved. Examinations of Michigan samples have consistently recovered a phomoid fungus from symptomatic tissue—visible as tiny black fruiting structures (pycnidia) within lesions—but preliminary DNA sequencing has not provided confident species identification .
“Symptom appearance alone is not sufficient, and detecting a fungus repeatedly in symptomatic tissue does not by itself establish that it is the causal agent,” MSU pathologists Martin Chilvers and Jan Byrne wrote in a bulletin .
Call for Samples
MSU researchers are asking growers, agronomists, and crop consultants to submit representative symptomatic leaves—preferably with fresh lesions—along with details on county, field location, hybrid, growth stage, and any recent fungicide applications. Samples that cannot be submitted immediately should be dried in a paper bag .
The investigation combines fungal isolation, morphology, DNA sequencing, and pathogenicity testing. Cornell University and Purdue University have also begun examining the disease .
Potential Impact and Management Gaps
In fields with heavy pressure, Chilvers has observed rapid dry-down of corn silage, early senescence of grain corn, stalk standability issues, and yield loss from reduced grain fill . He noted the situation is “giving me tar spot flashbacks,” referencing the destructive 2018 and 2021 epidemics, though comparable yield losses for white spot have not yet been established .
A significant challenge for growers: no fungicides are currently labeled for this disease in the U.S. Companies are exploring emergency exemption labels, and products used in Brazil have shown effectiveness but require U.S. testing and approval .
Crop Progress Context
According to the latest USDA Crop Progress report published October 19, 18% of Michigan’s corn crop had been harvested by the week ending October 18—significantly behind the five-year average of 31%. The state’s corn condition was rated 2% very poor, 9% poor, 38% fair, 32% good, and 19% excellent, generally better than the national average .
