Corn Diseases Raise Silage Concerns Ahead of Harvest Season

By Andi Anderson

Iowa’s corn fields are facing new challenges this summer as farmers prepare for silage harvest. Unusually hot and wet conditions have led to wrapped tassels, southern rust, and increased ear rot risks, all of which could affect silage quality and livestock feed safety.

Wrapped tassels, a rare occurrence in the Midwest, have been widely reported this year. Iowa State University Extension specialists believe they result from rapid growth under conditions of high moisture, heat, and nutrients. Tassels emerge before the flag leaf can unfurl, leading to incomplete pollination.

While overall yield and nutrients are not expected to decline significantly, poor pollination can reduce starch levels, a critical factor for high-quality silage.

Southern rust poses a more serious concern. First identified in Iowa in July, it has spread quickly due to warm and wet weather.

Although the disease does not produce toxins itself, it weakens plants and increases the risk of stalk rots like Fusarium and Gibberella, which generate harmful mycotoxins. These can impact feed safety if left unchecked.

Research shows southern rust can also accelerate plant dry down, making ensiling more difficult. Low plant moisture prevents proper packing, raising silage pH and increasing the risk of poor fermentation.

In addition, disease in the upper canopy can reduce grain fill, lowering starch levels in silage. Fiber content has also been shown to rise, reducing digestibility by as much as 13 percent.

Beyond tassels and rust, ear rots including Gibberella, Fusarium, and Diplodia are thriving in this year’s wet weather. These fungi are particularly concerning for their potential to produce mycotoxins harmful to livestock.

Experts recommend testing silage for toxins before feeding. The Iowa State University Veterinary Diagnostic Laboratory offers testing services and resources for safe feed management.

Farmers are also encouraged to review guidance from the Crop Protection Network for identifying ear rots and other corn diseases.

As harvest nears, close monitoring and proactive testing will be essential to protecting silage quality and livestock health.

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