Soybean plant infected with frogeye leaf spot.

Unpredictable weather and high-moisture levels presented their fair share of challenges in 2019. In addition to planting and harvesting delays, these conditions also spread new diseases to the area, many of which could reappear this season. Although not necessarily new for some states, tar spot in corn and strobilurin-resistant frogeye leaf spot (FELS) in soybeans present growing risks for Midwest territories. Here’s what you need to know to stay ahead of these yield-reducing diseases.

Tar Spot in Corn

Tar spot has been confirmed in 9 states since 2015, and over the past couple years has been spreading quickly, working its way from the upper Midwest down into the region’s center. Research from Purdue Extension says tar spot favors the following conditions, and based on last year’s weather could be the reason the disease is moving faster than anticipated:

• Cool temperatures (59-70 F°).
• Humid conditions (85% relative humidity).
• Long periods of leaf wetness (greater than 7 hours).
• Wind-driven rain and storms.

Symptoms, according to University of Illinois Extension:

• Small, raised, black spots (ranging from circular to oval).
• Tan or brown halo surrounding the spots (may appear on both sides of the leaves, leaf sheaths and husk).

Strobilurin-resistant FELS in Soybeans

Strobilurin-resistant FELS has been primarily present in the South for years. However, in 2019, Iowa State Extension plant pathologists recorded 73 cases of the diseases across 51 Iowa counties, confirming FELS is spreading each year.

According to University of Wisconsin Extension researchers, the disease thrives in the following conditions:

• Warm temperatures (77-86 F°).
• Humid conditions (>90% relative humidity).
• Frequent cloudy days and extended periods of wet weather.

Symptoms, according to the University of Nebraska-Lincoln:

• Small, dark spots on the leaves (¼ inch diameter).
• Center lesions become gray to brown and have a reddish-purple margin.
• Irregular patterns of blighting on the leaf.

To help prepare and fight against diseases like tar spot and strobilurin-resistant FELS, we recommend applying a broad-spectrum, preventive option like Miravis® Neo fungicide. It has 3 separate modes of action to help delay resistance and is extremely effective against leaf spots and blights in corn and soybeans. Miravis Neo contains Adepidyn® fungicide, one of the highest-performing, broad-spectrum SDHI molecules available and has activity against strobilurin-resistant diseases.

With control of some of the most damaging diseases, Miravis Neo takes the guesswork out of corn and soybean disease management, maximizing yield and ROI potential.

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