Telling corn ear rots apart
Sept. 10, 2019
According the The Ohio State University Agronomic Crops Network (OSU Extension), ear rots differ from each other in terms of the damage they cause, the toxins they produce and the specific conditions in which they develop.
A good first step for determining if you have an ear rot problem is to walk fields between dough and black-layer, before plants start drying down, and observe the ears. Peel back the husk and examine suspect ears for typical ear rot symptoms: husks of affected ears usually appear partially or completely dead (dry and bleached), often with tinges of the color of the mycelium, spores or spore-bearing structures of fungus causing the disease. Depending on the severity of the disease, the leaf attached to the base of the diseased ear (the ear leaf) may also die and droop causing affected plants to stick out between healthy plants with normal, green ear leaves. To determine the severity of the problem, count the number of moldy ears out of 50 ears examined in multiple locations across a field.
DIPLODIA EAR ROT is one of the most common corn diseases in Ohio. Diplodia has white mycelium fungus growing over and between kernels, usually starting from the base of the ear, making it easy to identify. Under highly favorable weather conditions, entire ears may become colonized, turn grayish-brown in color and be lightweight (mummified), with kernels, cobs and ear leaves that are rotted and soft. Rotted kernels may germinate prematurely, particularly if the ears remain upright after physiological maturity. Corn is most susceptible to infection up to three weeks after R1. Wet conditions and moderate temperatures during this period favor infection and disease development, and the disease tends to be most severe in no-till or reduce-till fields of corn planted after corn. The greatest impact of this disease is grain yield and quality reduction. Mycotoxins have not been associated with this disease in Unites States, although animals often refuse to consume moldy grain.
When natural early-season infections occur via the silk, GIBBERELLA EAR ROT typically develops as white to pink mold covering the tip to the upper half of the ear. However, infections may also occur at the base of the ear, causing the whitish-pink diseased kernels to develop from the base of the ear upward. This is particularly true if ears dry down in an upright position and it rains during the weeks leading up to harvest. Gibberella ear rot may also infect plants via wounds made by birds or insects, which leads to the mold developing wherever the damage occurs. When severe, Gibberella ear rot is a major concern because the fungus produces several mycotoxins, including deoxynivalenol (vomitoxin), that are harmful to livestock. Once the ear is infected by the fungus, these mycotoxins may be present even if no visual symptoms of the disease are detected.
FUSARIUM EAR ROT is especially common in fields with bird or insect damage to the ears. Affected ears usually have individual diseased kernels scattered over the ear or in small clusters (associated with insect damage) among healthy-looking kernels. The fungus appears as a whitish mold and infected kernels sometimes develop a brownish discoloration with light-colored streaks called “starburst”. Several different Fusarium species are associated with Fusarium ear rot, some of which produce toxins called Fumonisins.
TRICHODERMA EAR ROT appears as sprouting (premature germination of the grain on the ear in the field) and as an abundant, thick, greenish mold growing on and between the kernels, making it very easy to identify. Be careful, though, other greenish ear rots such as Cladosporium, Penicillium and Aspergillus are commonly mistaken for Trichoderma ear rot.