Reduce Risk of Mycotoxin Contamination by Scouting Fields for Ear Rot

August 25, 2011
ICM News

Alison Robertson, Department of Plant Pathology and Microbiology; and Charles Hurburgh, Iowa Grain Quality Initiative

Hail storms damaged several corn and soybean fields in parts of Iowa last week. In some areas, the corn and beans are completely lodged as a result of the storm. In other areas, leaves are significantly stripped, but the grain seems relatively undamaged. 

During the 2009 growing season, approximately one million acres of crops from Sac to Grundy Counties were damaged by a single hail storm. Most of the corn crop was at growth stage R2.  We conducted a survey to assess the impact of hail damage on grain quality (Robertson et al., 2010). We found that hail damage to kernels increased the risk of ear rot and mycotoxin contamination.

Scout for ear rot

The corn that was damaged in the hail storms last week was further along in development (growth stage R5) than the grain damaged in 2009, but it still may be at risk for ear rots and associated mycotoxin contamination. Fields that were damaged need to be scouted in the next 10 to 14 days for ear rot. If more than 10 percent of the ears in a field are moldy, the field should be scheduled for an early harvest. Check with your insurance company regarding their requirements for claims. Most companies will want to assess the field before it is harvested.

Fields that were not damaged by hail should also be scouted for ear rot, since the hot, dry weather with occasional rain that has occurred recently is favorable for Aspergillus and Fusarium ear rot development. Symptoms of Aspergillus ear rot are a powdery olive-green mold that develops on damaged kernels (Figure 1). High temperatures (80 to 100 F) and high relative humidity (85 percent) favor the growth of Aspergillus in the field. Note that the presence of Aspergillus ear rot does not necessarily indicate aflatoxin contamination. Aflatoxins are produced under certain conditions, and are most often a problem when night temperatures remain above 70 F. The U.S. Food and Drug Administration regulates aflatoxin levels in food and livestock feed. An "action level" of 20 parts per billion (ppb) for aflatoxin in corn has been established for interstate commerce.

Fusarium ear rot symptoms are characterized by white to light pink mold that usually occurs on damaged kernels (Figure 2).  High temperatures (above 77 F), drought stress before or after silking and mechanical damage favor infection and the development of Fusarium ear rot. Mycotoxins associated with this ear rot are fumonisins, and the optimum temperature for fumonisin production is 75 F (which is cooler than that for aflatoxin). Bush et al (2003) found fumonisin concentrations increased from physiological maturity, thus early harvest may help reduce the level of contamination. The U.S. Food and Drug Administration (FDA) has guidelines for safe levels of fumonisins in corn used for foods and animal feeds. Fumonisins are acutely toxic to animals (especially pigs and horses), and have been linked to increased cancer rates and other human health problems.

aspergillus ear rot

Figure 1. Symptoms of Aspergillus ear rot are a powdery olive-green mold that develops on damaged kernels.

Fusarium ear rot

Figure 2. White to light pink mold is a characteristic of Fusarium ear rot.


Bush et al.  2004.  Phytopathology 94:88-93

Robertson et al. 2010.  Agronomy Journal 103: 193-199. 

Alison Robertson is an associate professor in the Department of Plant Pathology and Microbiology with extension and research responsibilities; contact her at or phone 515-294-6708. Charles Hurburgh is a professor of Agricultural and Biosystems Engineering and professor in charge of the Iowa Grain Quality Initiative; contact him at or 515-294-8629.

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on August 25, 2011. The information contained within may not be the most current and accurate depending on when it is accessed.


Alison Robertson Professor of Plant Pathology and Microbiology

Dr. Alison Robertson is a professor of plant pathology and microbiology. She provides extension education on the diagnosis and management of corn and soybean diseases. Her research interests include Pythium seedling disease of corn and soybean and Goss's wilt. Dr. Robertson received her bach...

Charles Hurburgh Professor, Agricultural and Biosystems Engineering

Dr. Charles R. Hurburgh, Charlie to most everyone, is a native Iowan from Rockwell City (Iowa, USA). He continues to operate the family farm, and is a professor of Agricultural and Biosystems Engineering at Iowa State University. He has a bachelor's degree, master's degree, and doctoral degree fr...