7/19/2020

Field Facts: Tar Spot

Tar spot is a corn disease that is caused by the fungus Phyllachora maydis. The pathogen started appearing in Midwest states over the last few years. It can currently be found in states such as Iowa, Illinois and Indiana. A tar spot infection can cause severe yield loss if left untreated.

Symptoms — Small, raised black dots appear on leaves, both on the upper and lower surfaces. These spots cannot be easily scraped off affected leaves. So-called “fisheye” lesions can also develop. These are tan or brown lesions with darker borders.

Geography — Tar spot can be found in the Midwest, specifically across most of Iowa, Illinois and Indiana, with pockets in northwestern Ohio, lower Michigan, southern Wisconsin and southeastern Minnesota. The disease continues to spread season by season. It originated in South America and Central America

Timing — Late spring to early fall

Conditions for development — High humidity and periods of consistent rain with temperatures ranging from 59 F to 70 F

Scouting tips — Corn can be affected at any stage in development. Scout regularly, particularly when conditions are right. Spores from the fungus can be spread by wind and rain. Because this is a relatively new disease in the United States, if you suspect tar spot, send an affected plant to your state diagnostic lab for confirmation.

Effect on yield — The disease can cause more than 50% yield loss if left untreated.

Management tips — Choose resistant corn varieties with your retailer, rotate crops, till fields to encourage decomposition of infected residue and apply a fungicide preventively or, if necessary, curatively. Aproach® Prima fungicide is a good choice for controlling tar spot. Explore all the corn diseases Aproach Prima controls on Corteva.us.

™ ® Aproach Prima is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Always read and follow label directions..