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.
Figure 1. Symptoms of Aspergillus ear rot are a powdery olive-green mold that develops on damaged kernels.
Figure 2. White to light pink mold is a characteristic of Fusarium ear rot.
Source: Alison Robertson, Department of Plant Pathology and Microbiology; and Charles Hurburgh, Iowa Grain Quality Initiative
Bush et al. 2004. Phytopathology 94:88-93
Robertson et al. 2010. Agronomy Journal 103: 193-199.