COLUMBIA, Mo. – University of Missouri Extension state specialists will cover a variety of topics July 10 at the annual Crop and Pest Management Field Day at MU’s Bradford Research Farm in Columbia. MU Extension plant pathologist Mandy Bish will address tar spot and red crown rot, two diseases that threaten Missouri corn and soybean yields.

A decade of tar spot

Tar spot is likely to appear in Missouri cornfields, especially in northern Missouri, by mid-to-late June, says Bish. It has been 10 years since tar spot was first spotted in Illinois and Indiana and began spreading across the Midwest. Tar spot was first confirmed in northern Missouri in 2019 and has now been identified in 63 counties in the state.

Unfortunately, it is here to stay, says Bish, so growers need to understand how to best manage it.

Yield losses can be substantial – 20 to 40 bushels per acre during severe outbreaks. However, Bish notes that not every year will see a severe outbreak.

Confirmation does not mean the disease is severe enough to warrant fungicide applications. Bish will give recommendations on in-season management and discuss application timing, return on investment and identification tips.

Red crown rot: an emerging threat to soybean

Bish will also discuss red crown rot, a soybean disease confirmed in Missouri for the first time in 2024. Yield losses can range from 15% to 70% in affected areas. The fungus survives the winter in plant residue and prefers warm and wet conditions for growth.

Bish recommends careful scouting and a “roots up and stems split” approach: Dig up symptomatic soybean plants to examine roots and split the stems open to distinguish red crown rot from sudden death syndrome and other conditions that cause similar symptoms on soybean leaves.

Save the date

Registration for the field day will be available soon at https://extension.missouri.edu/events, Bish says. She and MU Extension weed scientist Kevin Bradley urge interested parties to save the date of July 10 for this popular annual event.

Photos

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Tar spot, a yield-robbing disease of corn, can be identified by small, raised black spots across the upper and lower leaf surfaces. Photo courtesy of Mandy Bish, MU Extension plant pathologist.

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Leaves of soybean plants infected with red crown rot can have symptoms that resemble sudden death syndrome. Yellow spots become visible on upper canopy leaves and can progress into yellow and brown spots that grow between leaf veins. Photo courtesy of Mandy Bish, MU Extension plant pathologist.