The northern U.S.’s most damaging corn disease in 2022 is expected to spread and continue to be a challenge this year, prompting farmers to consider more effective mitigation efforts even before the planting season begins.

The Crop Protection Network reports that tar spot was responsible for 116.8 million bushels of corn yield losses across 14 states during the 2022 growing season from Colorado to Ohio and Wisconsin to Kansas, including Iowa.

While relatively new — first detected in Indiana and Illinois in 2015, tar spot quickly has become one of the most damaging corn diseases because hybrids don’t yet have good resistance to it, says Alison Robertson, Iowa State University (ISU) Extension field crops pathologist.  

She suggests starting now when...