Scout For Corn Ear Rots

 

 

 

A number of corn fields scouted in the northeast and east-central counties were found with corn ear rots. Corn ear rots were mostly prevalent in areas that experienced hail storms recently (Figure 1). Corn ear rots are caused by a number of fungal pathogens and which one will develop depends on weather conditions.

 

 

Fusarium ear rot develops under hot dry weather and infection occurs at or after flowering. The fungus infects the corn ear through silk and wounds created by hail injury and insects. Occasionally, Fusarium stalk rot can develop systemically and cause ear rot. Several Fusarium species cause ear rot but the most common species are F. verticillioides and F. proliferatum. These Fusarium species overwinter in residue from corn and other plants.

 

The symptoms vary greatly depending on the genotype, environment, and disease severity. Individual infected kernels can be scattered in the ear (Figure 2). Under severe conditions, the entire ear may be consumed by the fungus. Infected kernels have whitish pink to lavender fungal growth.

 

This disease reduces yield and grain quality. The kernel can be completely consumed by the fungus and become contaminated with mycotoxins (fumonisins), which can be fatal to livestock (horses and pigs).

 

 

 

Gibberella ear rot, also called red rot, develops under prolonged rainy weather late in the growing season. Its symptoms are characterized by a reddish mold that appears at or near the tip and grows down the ear (Figure 3). Gibberella ear rot is caused by Gibberella zeae. This pathogen overwinters on corn debris and has a wide range of hosts including small grains. The fungus infects ears through the silk and progresses down the ear. Corn following corn is more prone to Gibberella ear rot development. This fungus produces mycotoxins (deoxynivalenol and zeralenone) in infected grain.

 

 

 

Aspergillus ear rot is the most important ear rot because it produces aflatoxins which are dangerous to humans and animals. Two common species Aspergillus flavus and Aspergillus parasiticus infect corn. Of these, Aspergillus flavus is the most predominant species. The fungus overwinters in soil and debris and infection is favored by hot, dry weather. The fungus is spread to silks by wind or insects. This disease can be important under drought conditions. Insect or hail damage predisposes the kernels to infection and Aspergillus ear rot development. In most cases only a few kernels on an ear are infected. Infected kernels have masses of olive to yellow green spores on and between them (Figure 4). Sporulation of the fungus is most evident on kernels that were injured. However the fungus can also be present on kernels without showing symptoms.

 

If Aspergillus ear rot is present in a field, the grain needs to be tested for aflatoxins. If concentrations are greater than 20 ppb, the grain cannot be sold or transported across state lines. The blending of corn to reduce aflatoxin concentrations is prohibited for interstate trade. If the grain is used for ethanol production, distillers’ grains obtained from that corn will have elevated aflatoxin levels.

 

 

 

Penicillium ear rot is caused by Penicillium spp and this ear rot is also important because of the mycotoxins associated with it. The most common mycotoxin is ochratoxin A. This mycotoxin is produced by Penicillium verrucosum. Penicillium ear rot is most common in ears with mechanical injury caused by insects or hail damage. Infected kernels have powdery green or blue-green mold (Figure 5).