Heavy rains followed by intense summer heat across the Corn Belt have created the ideal environment for southern rust and other corn diseases. Yet when it comes to silage, most infected corn remains suitable for livestock feed - as long as farmers closely inspect fields before harvest.

"This is a perfect year for disease pressure in corn fields with the amount of moisture we've had followed by the heat," said Shelby Gruss, Iowa State University Extension forage specialist. "We're likely to see some early dry down, so producers who are cutting silage need to get out in their fields and see what the corn looks like."

While southern rust alone may not compromise silage safety, when combined with stalk rot or ear rot, it could reduce quality. Most notably, ear rots like Gibberella, Fusarium, and Diplodia-prevalent in wet conditions-raise the risk of mycotoxin production.

Watch for Mycotoxins

Mycotoxins, which can stem from these ear rots, pose serious health threats to cattle. They may affect the liver, gastrointestinal tract, immune system, reproductive system, or kidneys. Gruss recommends that if producers are concerned, they should submit samples to the Iowa State Veterinary Diagnostic Lab for mycotoxin testing.

Another concern is poor grain fill, which could result from early dry down and pollination issues. According to Mark Licht, Iowa State Extension cropping systems specialist, wrapped tassels are being reported across the region. This can hinder pollination and result in lower starch content, a vital component in high-quality silage.

Scouting is Critical

Before chopping corn for silage, experts emphasize the need for full-plant field evaluations. "The most important thing is to look at the entire plant and walk out into the field to see what the plants look like within the field prior to cutting," Gruss noted.

If silage appears too dry, producers can add an inoculum to aid in compaction and improve fermentation. Once fermentation begins, producers should also monitor pH levels. An ideal pH range is 3.8 to 4.2. Anything above that may reduce silage stability, requiring it to be fed out earlier.

Post-Harvest Considerations for Grazing

For those grazing cornstalk fields after harvest, the risk from these diseases is less critical. Although digestibility may be reduced, stalks are primarily a fiber source, so the impact on livestock performance is limited.

Bottom Line for Livestock Producers

While disease pressure in cornfields is unusually high, corn intended for silage remains viable and safe with proper management. The keys are early scouting, moisture control, fermentation monitoring, and feed testing when risks like mycotoxins are suspected.