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AMES, Iowa — This summer has been both hot and wet, with consistent rainfall across much of Iowa. These conditions have led to some unusual challenges in corn fields, including wrapped tassels and southern rust.

Both have raised questions about their potential impacts on corn silage.

Wrapped tassels are not a common occurrence in Iowa or the Midwest. As noted by Iowa State Extension cropping systems specialist Mark Licht in a recent ICM blog post, he has only observed this phenomenon once in a 20-plus year career. Yet this year, wrapped tassels have been widely reported across the region.

Wrapped tassels are believed to result from high temperatures, abundant moisture and nutrient availability.

These conditions can cause the tassel to emerge before the flag leaf has had time to fully unfurl, similar to rapid growth syndrome seen in early vegetative stages.

For silage production as in grain production, the main concern lies in potential pollination problems.

Starch content, a key component of silage quality, comes from the ear, so poor pollination can lower starch levels in the final feed. While other nutrient components and total yield are not expected to be significantly affected, there is limited research on its implications due to the rarity of this issue.

Southern rust, on the other hand, may pose a more significant risk.

Since first being identified in Iowa in July, the disease has spread rapidly under warm, wet conditions.

Southern rust itself does not produce toxins, but it weakens the plant and can open the door for other diseases such as Fusarium and Gibberella stalk rots, which do produce mycotoxins (fumonisin and deoxynivalenol) that are harmful in feed.

Early dry down can disrupt the ensiling process. When whole-plant moisture is too low, silage becomes more difficult to pack tightly, which prevents the formation of an ideal anaerobic environment. This increases the risk of poor fermentation, including butyric acid formation, and results in higher silage pH levels.

While yield impacts are often most evident in grain harvest, silage yield and quality can also be reduced as disease severity increases.

Disease pressure in the upper canopy is particularly concerning because it affects grain fill. Since grain contributes most of the starch — and therefore energy — in silage, reduced grain fill can translate to lower starch content in harvested forage.

Beyond wrapped tassels and southern rust, the wet conditions this summer have created significant disease pressure overall.

Ear rots such as Gibberella, Fusarium, and Diplodia thrive in wet conditions and are especially concerning because of the ability to produce mycotoxins that impact livestock health.

If you are concerned about disease impacts or potential toxins, getting your silage tested is a smart step to ensure feed safety. The Iowa State Veterinary Diagnostic Laboratory offers mycotoxin testing.