Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu; @Delmarplantdoc
Increased levels of ear rots in field corn are typically associated with wet weather in September. Ear rots are caused by several fungal pathogens, but most often we see observe those that are caused by Gibberella, Aspergillus, Fusarium and Diplodia. The main issue associated with these ear rots (Except Diplodia) is the production of mycotoxins, which can be affect the safety and quality of grain used for feed and ethanol production. Thus, it is important to be able to identify which organisms you are encountering.
Gibberella ear rot (Figure 1a) is the same fungus that causes Fusarium head blight in small grains. The reason the name differs has to do with fungal reproduction and the types of spores produced. Gibeberella infects through the silks and is typically observed at the tips of the ears and develops down the cob. The fungus produces a red to pink growth on and in-between kernels, and can produce vomitoxin and zeareleone.
Aspergillus (Figure 1b) has a powdery, olive green appearance and typically occurs on damaged kernels. Aspergillus is more of an issue in dry seasons. Aflatoxins are produced by this fungus.
Fusarium ear rot Figure 1c) can be caused by multiple species of Fusarium and is the most commonly occurring ear rot we encounter. A starburst appearance or streaks in kernels, as well as a white to pink growth in-between kernels is typically observed. Research we conducted with Virginia Tech indicated that this fungus and the fumonosins it can produce can be increased by stinkbug damage to the cob.
Figure 1. Different ear rots encountered in field corn grown in Delaware. a) Giberella ear rot; b) Aspergillus ear rot; c) Fusarium ear rot.
Hybrids with cobs prone to exposed ends as well as insect and bird damage can increase corn ear rots. General management of ear rots should focus on selecting hybrids with resistance or reduced susceptibility to commonly occurring ear rot fungi, rotating crops and sizing residue to enhance residue decomposition, and managing insects that can damage the cob. Fungicides can reduce some ear rots, but experimental results have not been consistent. For example, Anderson et al. (2017) studied the impacts of Quilt Xcel, Proline, and Headline applied at R1 on Gibberella ear rot and associated mycotoxins. The researchers inoculated corn with the fungal pathogen to ensure it would be present during the study. Their results showed that Gibberella ear rot consistently reduced yields but fungicides did not consistently reduce mycotoxin content of the grain. This article and other references to similar studies can be viewed here: https://www.plantmanagementnetwork.org/php/elements/sum2.aspx?id=10992