Ear Rots

Ear rots are some of the most important corn diseases throughout the United States and Canada. Ear rots decrease yield and can greatly reduce grain quality.

It is critical to identify ear rots in the field because many of the fungi responsible for ear rots produce toxic chemicals (known as mycotoxins), which can harm livestock and humans. Grain that has been contaminated with mycotoxins can be difficult to market and may be docked in price.

Dry infected grain to avoid further mycotoxin accumulation.
Dry infected grain to avoid further mycotoxin accumulation.

Therefore, it is important that farmers and other agricultural personnel are able to diagnose corn ear rots and manage affected grain according to the specific ear rot present. This publication:

  • Describes how to identify the most common corn ear rots observed in the United States and Canada
  • Discusses the mycotoxins associated with each ear rot
  • Describes diseases and disorders easily confused with corn ear rots
  • Briefly addresses how to manage ear rots and affected grain

Scouting for Ear Rots

To manage and minimize the effects of these ear rot diseases, it is critical to assess fields before harvest. You should assess fields each year, because these pre-harvest assessments can alert you to potential problems and provide time for livestock producers to segregate, obtain alternative grain, or hold onto stored corn from the previous year.

Scouting practices are similar for all corn ear rots. Begin scouting fields at late dent stage to determine the presence and severity of ear rots. When scouting, randomly select plants and pull back the husk to examine the entire ear. A quick method is to select 100 plants across the field (20 ears each from five different areas). For each ear, be sure to peel back the husks and examine the entire ear.

When scouting for corn ear rots, pull back the husk to examine the entire ear.
When scouting for corn ear rots, pull back the husk to examine the entire ear.

If a field contains a significant level of ear mold, collect a representative sample at harvest and have it tested for mycotoxins before storing the grain or feeding it to livestock. A lab test is often the only reliable way to definitively diagnose an ear rot or mycotoxin.

More information about grain sampling and mycotoxin testing is available in Corn Disease Management: Grain Sampling and Mycotoxin Testing (CPN-2003).

If you suspect a field is contaminated with a mycotoxin, contact your crop insurance agent. If you need to file a claim, your agent may require an adjuster to visit the field before harvest.

Managing Ear Rots

Corn infected by ear rots will often result in significant discounts on the grain. Kernels with an ear rot disease can be lighter than healthy kernels (which will lower the test weight of a sample), and elevators can dock grain that contains mold. Mycotoxin contamination can lead to further discounts.

General management practices apply to most ear rots.

Choose what you plant carefully. In fields with a history of ear rots, choose a corn hybrid that is less susceptible to the specific ear rot. You may also want to select hybrids with insect resistance traits, which can help reduce the occurrence of ear rots.

Promote conditions that favor healthy plant growth and reduce plant stresses. Make sure plants receive adequate water and nutrients, and minimize insect-related and other damage.

Don’t rely on fungicides. It is important to note that the foliar fungicides currently available are not generally recommended to manage ear rots and mycotoxins. There may be some fungicides available for Gibberella and Fusarium ear rots in the United States, but these products currently require a FIFRA Section 2(ee). Check with your state extension service (or in Canada, with the Pest Management Regulatory Agency) before using fungicides to control corn ear rots.

In areas with high levels of Aspergillus ear rot and a history of frequent aflatoxin contamination, consider using an atoxigenic fungal strain to reduce aflatoxin accumulation. More information about using atoxigenic strains to manage aflatoxin can be found in Corn Disease Management: Using Atoxigenics to Manage Aflatoxin (CPN-2005).

Harvest infected fields early and segregate the grain. Leaving diseased grain in the field allows the ear rot fungi to keep growing, which will increase the risk of moldy grain and mycotoxin contamination. Most ear rot fungi continue to grow (and, if applicable, produce mycotoxins) until the grain has less than 15 percent moisture. In severely infected fields, it may be worthwhile to harvest grain at a higher moisture and then dry it to less than 15 percent to minimize the further mycotoxin accumulation.

Never mix grain from a field affected by ear rots with grain from a field that has not been affected.

During harvest, adjust the combine to discard lightweight or damaged kernels. These kernels may contain mold and mycotoxins. Segregate poor-quality grain from good-quality grain, and clean moldy grain out of your equipment before using it on clean grain to prevent cross-contamination.

Storing Affected Grain

It is crucial to properly store corn affected by ear rots. You must quickly dry and cool grain after harvest to limit fungal growth and the further mycotoxin accumulation in storage.

The standard recommendations for long-term storage are to dry contaminated grain to less than 13 percent moisture and to cool it to 30°F (-1°C). Whenever possible, only store affected grain during the cold weather season.

More information about storing grain is available in Corn Disease Management: Storing Mycotoxin-affected Grain (CPN-2004).


Last updated – August 2016