Michigan State University researchers are collecting samples to identify a new leaf spot disease in Michigan corn that resembles symptoms historically described as Phaeosphaeria leaf spot (PLS) or maize white spot (MWS), Michigan Farm News reports.

What first looked like a local problem has now been seen in about 14 Michigan counties, with further reports from colleagues in New York and Pennsylvania. In affected fields, the disease has appeared with notable incidence and severity.

It is not yet known which fungus is responsible. Preliminary DNA sequencing has not given enough resolution to identify the species, and although older literature links PLS/MWS to Phaeosphaeria maydis, the identity of organisms given that name remains unresolved. Michigan samples have consistently yielded a phomoid fungus, visible under magnification as small black fruiting structures (pycnidia) inside the lesions — but finding a fungus repeatedly in diseased tissue does not by itself prove it is the cause.

The team is combining fungal isolation, morphology, DNA sequencing and pathogenicity testing to pin down the causal agent, which would allow a reliable diagnostic test and wider surveys of how far the disease has spread. The researchers also want information on severity and any yield or grain-quality effects.

Growers, agronomists and crop consultants are asked to report fields with similar symptoms and send several symptomatic leaves with fresh lesions, noting county, hybrid, growth stage and any fungicide use, to Martin Chilvers of MSU's Department of Plant, Soil and Microbial Sciences; samples that cannot be sent at once should be dried in a paper bag.

Photo: Dwight Burdette / Wikimedia Commons (CC BY 3.0)

Source: Michigan Farm News