Gibberella and Fusarium ear rots were found in scouted corn fields in Brookings, Moody, and Deuel counties. Corn, in areas where there has been prolonged rainy weather, should be scouted for ear rots in order to make decisions for corn harvesting and drying.
Gibberella Ear Rot
Gibberella ear rot (also known as red rot), is characterized by a reddish mold which appears at the tip and grows down the ear (Click to view image, ear on the right). Gibberella ear rot is caused by Gibberella zeae (syn. Fusarium graminearum). This pathogen overwinters on corn debris and has a wide host range which also includes small grains. The fungus infects the ear through the silk and continues to progress down the ear.
This disease is favored by cool, wet weather just after silking. Corn following corn is more prone to Gibberella ear rot development. The concern with this fungus is that it produces mycotoxins (deoxynivalenol and zeralenone) in the infected grain.
Fusarium Ear Rot
Fusarium ear rot usually develops when kernels are damaged by birds, insects or hail. Several Fusarium species cause ear rot but the most common species are F. verticillioides and F. preliferatum. These Fusarium species overwinter in corn residue. Occasionally, Fusarium stalk rot can develop systemically to cause ear rot.
Fusarium ear rot symptoms vary greatly depending on the hybrid and environment. Individual infected kernels can be scattered in the ear (Figure 1, left ear) and under severe conditions, the entire ear may be consumed by the fungus. Infected kernels have whitish pink to lavender fungal growth. Fusarium fungi may produce Fumonisin mycotoxins.
Scouting fields before harvest is an important management step needed to determine the amount of ear rot in a field and consequently if there is a risk of mycotoxin contamination of grain.
Scout fields by peeling back the husks and inspecting at least 10 ears and at a minimum of 5 random stops throughout the field.
If greater than 10% of ears in a field have >10-20% moldy kernels, the field should be scheduled for harvest as early as possible. Care should be taken not to damage kernels during harvest. The grain should be cooled and dried to <15% moisture content immediately after harvest. Grain from fields where ear rot was a problem should be stored in a separate bin from fields where the ears were healthy. Crop rotations, residue management, insect management, and hybrid selection are some of the practices which can reduce ear rots in future growing seasons.