Author: Kiersten Wise
Planning Unit: Plant Pathology
Major Program: Integrated Pest Management
Outcome: Intermediate Outcome
The disease tar spot, caused by the fungus Phyllachora maydis, was first discovered in the United States in 2015. Since 2015, tar spot has become a major corn disease in the Midwest, causing yield losses up to 60 bushels per acre in fields where it is established. The disease was confirmed via laboratory diagnosis in two counties in Kentucky in 2021. In 2022, a state-wide monitoring program was funded by the Kentucky Corn Growers Association to scout for tar spot. Over 84 fields in 12 counties were scouted at least once from July to September, and 24 fields were monitored intensively, with multiple scouting trips in July and August of 2022. None of the scouted fields had symptoms of tar spot. The disease was confirmed in Lincoln County in September of 2022, but did not affect yield in that field. This scouting effort complements a USDA-NIFA funded project (0500-00102-001-011S) that monitors field-level fungal inoculum and ties inoculum levels detected to actual disease that develops in a field. These field-level data from the University of Kentucky Research and Education Center, in Princeton, KY, are all contributed to a free, nationally available disease management decision tool called Tarspotter. Having inoculum collection and scouting results for this new disease helps determine where and when management may be needed for tar spot in Kentucky, and currently saves farmers up to $36 per acre in unnecessary fungicide application costs to manage the disease. For a farmer growing 1,000 acres of corn, this is an annual savings of up to $36,000 for their farm. We continue to monitor and study this disease in Kentucky so we can understand its longer-term impact on yield and disease management in corn.
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