Epidemiology and management of corn tar spot, a new disease for the United States

MSU scientist Martin Chilvers has assisted growers by providing data on best management practices to minimize losses from corn tar spot.

Researcher: Martin Chilvers
Awarded: $40,000
Leveraged: $715,000

Tar spot is a disease of corn previously reported in Mexico and Central America. In 2015, tar spot was found for the first time in the U.S., in Indiana and Illinois. As the name suggests, tar spot looks and feels like black spots of tar, which cannot be easily rubbed off the leaf surface. The black structures are fungal fruiting bodies that release spores to infect the plant and are capable of overwintering in debris. To scout for the disease, it is important to inspect plants carefully, as light infections can be hard to see, and are often missed during scouting. However, once disease takes off it is often possible to see heavy infestations from the air.

Since the initial 2016 confirmation of tar spot in Michigan, the lab of Martin Chilvers, an associate professor in the MSU Department of Plant, Soil and Microbial Sciences, with assistance of farmers and private ag consultants, has tracked the spread each year across the state. Initially tar spot was confirmed in Allegan County, Michigan, in 2016 and again in 2017. By 2018, the disease had been found at alarming incidence and severity levels across many fields, particularly around the site of origin in Allegan County. Unfortunately, this disease can be incredibly destructive. Tar spot continued to spread and cause losses in 2019 and 2020, but those summers were not overly wet, so losses were moderate. However, with wet summers in both 2018 and 2021, greater yield losses were confirmed.

Chilvers’ work has supported Michigan corn farmers by providing data on best management practices to minimize losses from this disease. The team has examined the role of agronomic practices, such as planting population, nitrogen fertility practices, fungicide product choice and timing, and the role of hybrid resistance in disease management.

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