Keeping grain clean: Managing Gibberella ear rot, mycotoxins 

By Camila Nicolli, Purdue College of Agriculture 

When walking your fields late in the season, spotting a moldy ear is always frustrating. However, from a management and marketing standpoint, not all ear rots develop equally. While some molds simply damage physical kernel quality, others introduce a hidden, costly threat – the mycotoxins. 

For Indiana growers, understanding which fungi produce these chemical compounds is essential for protecting grain safety, livestock feed quality and local market value. As a Research Assistant Professor in Mycotoxin Fungal Biology in the Department of Botany and Plant Pathology at Purdue University, I was appointed this past January to study mycotoxins. 

Purdue is developing the “CropTox Care” program (ag.purdue.edu/department/btny/labs/nicolli/index.html), which is dedicated to safeguarding crop quality, supporting resilient production systems and delivering practical, science-based solutions for managing mycotoxins from field to storage. 

Mycotoxin producing species 

Certain fungal pathogens do double damage; they rot kernel tissue and contaminate it with dangerous toxins that pose severe health risks to livestock and humans. Crucially, ears do not have to look severely moldy to be highly toxic, also sometimes one single spot or even one single kernel can have a high levels of mycotoxins, which leads to sampling being a critical point. 

Mycotoxins can accumulate without obvious visual symptoms, often driven by late-season stressors or insect damage. Figure 1 provides a detailed illustration of the most important mycotoxin-producing fungal species, highlighting their associated colors and symptoms. 

Mycotoxin production is not a single event; it is a process that unfolds across the entire growing season and can continue stubbornly even after the combine leaves the field. Understanding this timeline is key to mitigating contamination risk: 

• Silking (The Entry Point) – Infection begins at silking, which serves as the primary entry point for fungi like Fusarium and Aspergillus. Spores enter directly through the silks, and their success is amplified by insect damage or heat and drought stress that weaken plant defenses. 

• Grain Fill (Accumulation Begins) – As kernels develop, fungi already present in the ear start producing mycotoxins if conditions turn favorable. Warm temperatures and drought-stressed plants are especially vulnerable. Toxins like deoxynivalenol (DON), zearalenone (ZEA), fumonisin (FB) and aflatoxin (AFLA) can actively accumulate during this stage, even in the complete absence of visible ear rot symptoms. 

• Pre-Harvest (The Critical Window) – Late-season weather plays a massive role in determining final toxin levels. It is highly common for mycotoxin levels to surge right before harvesting, even if the infection occurred months earlier. Delayed harvest simply gives the fungi more time to grow and produce toxins. 

• Post-Harvest and Storage (The Overlooked Stage) – One of the most frequently missed steps in risk management happens in the bin. If grain is stored with high moisture, warm temperatures or poor aeration, fungi remain active. Problems that start as minor issues in the field can easily intensify into major financial losses once the grain is in storage. 

Weather is ultimate risk driver 

Every corn grower has seen it. One year delivers pristine grain, while the next brings unexpected ear rots and high mycotoxin dockage under the exact same management practices. What changed? The weather. While weather is the least controllable factor in agriculture, understanding how environmental conditions drive regional risk patterns can help you anticipate contamination.  

Frequent heat and drought stress during flowering and grain fill heavily favor Aspergillus flavus, making aflatoxin a dominant threat in the southern United States. 

In states like Indiana, temperate and humid conditions paired with frequent rainfall during silking create the perfect environment for Gibberella ear rot, leading to elevated risks of DON, also known as vomitoxin and zearalenone.  

Fusarium ear rot thrives in moderate to warm temperatures during silking, backed by wet conditions prior to harvest. Furthermore, fields with heavy insect pressure routinely exhibit significantly higher fumonisin levels. 

Proactive management 

Farmers cannot change the weather, but corn growers can change how they prepare for it. Ear rot diseases and mycotoxin contamination are driven by the interaction of weather, pathogens and crop conditions throughout the growing season. 

To move from reactive troubleshooting to proactive protection, growers can utilize advanced digital tools to assess risk before symptoms ever appear. For Gibberella ear rot, the Crop Protection Network (CPN) offers a free, data-driven forecasting tool to help growers decide if and when to apply a fungicide to manage mycotoxins. 

CPN will guide farmers in data discovery: 

• How it works – The tool utilizes live weather data based on the precise GPS location of each individual field. 

• The Output – It calculates the estimated percentage risk of Gibberella ear rot occurring, giving farmers the potential risk of mycotoxin contamination. 

• Timing is Everything – To get an accurate forecast and make a timely management decision, farmers must utilize the tool 7-15 days prior to silking. 

Farmers should check their fields and evaluate their regional risk soon by visiting the tool online at connect.doit.wisc.edu/cpn-risk-tool. 

Integrated management strategies 

Our program will continue evaluating the efficacy of commercially available fungicides and developing integrated management strategies to reduce mycotoxin contamination in Indiana corn. 

Through a project submitted to the Indiana Corn Marketing Council, titled Protecting Grain Quality: A Production-Based Strategy to Mitigate Mycotoxin Risks in Indiana Corn, and upon approval, we will conduct field research on hybrid resistance, fungicide efficacy, planting date, harvest timing and green silk applications; collect statewide metadata and grain samples to improve Indiana-specific mycotoxin risk prediction models; and establish a fungal collection to identify predominant Fusarium species and associated mycotoxins, including DON, fumonisins, zearalenone, and T-2 toxin. 

Together, these efforts will generate science-based recommendations to reduce ear rot, improve grain quality, and increase grower profitability.