Regions throughout Illinois and Indiana have been experiencing increased rainfall during and after pollination, which can cause favorable conditions for corn ear rot development.

For growers experiencing ear rot pressure, it’s best to harvest as soon as the grain reaches 25 percent, and then dry the grain quickly to below 15 percent moisture (preferably to 13 percent moisture). This will help to minimize spreading within the stored grain.

Affected growers can also consider adjusting the fan speed of their combine. If they have a rotary grain cleaner, growers are advised to lower their fan speed when unloading grain before storage to help remove lighter kernels and fines. Growers who don’t have a rotary grain cleaner can turn up their fan speed to help blow out light and damaged kernels, although they should be mindful that the increased speed can inoculate the field for future crops.

Below is an overview of the major types of corn ear rots below to aid in scouting and identification efforts.

Major types of corn ear rots:

Diplodia ear rot starts at the base of the ear and works its way up, often infecting the whole ear. It is a dense, white mold that becomes grayish-brown and has raised black fruiting bodies that can be seen later in the season. This disease is often favored by wet weather just after silking and is more severe in corn-on-corn fields.

While Diplodia ear rot does not produce a toxin, it produces a lighter test weight (TW) kernel and discoloration, which may cause dockage when delivering the grain. Residue on the soil surface can be a prime inoculate environment. Even residue from two years ago in no-till or reduced tillage situations can be a factor as corn is the only known host crop.

Diplodia ear rot can spread by wind or rain. The level of this disease within a field is highly proportional to the amount of infected corn residue on the soil surface.

Diplodia ear rot

Gibberella ear rot almost always starts at the tip of the ear and works its way down the ear. The initial mold infection may be very pale and white, but as the mold progresses, growers may see the mold develop to a red or pink color. Growers should keep in mind that this is the same fungus that causes head scab in wheat, so there is another host crop to be aware of for management and potential inoculate issues.

Infection is caused by cooler, wetter weather during and after pollination, and occurs through the young silk stage. This can, again, reduce TW and impact grain quality with discolored kernels and kernel damage. Gibberella ear rot also develops vomitoxin, a toxin that may cause elevators to reject loads if the level is too high. Vomitoxin can cause feed refusal and poor weight gain especially in swine.

Gibberella ear rot

Fusarium ear rot is identified by scattered or random grouping of affected kernels. Early infection typically shows “starburst” white streaking in the affected kernels, which starts at the top of the kernel and streaks down the sides. This can happen because the point of infection is where the silk attached to the kernel ovule. Streaked mold often starts out white and may later turn pink or salmon-colored.

Fusarium ear rot produces fumonisins, which are highly toxic to some species, especially horses, dogs, and rabbits. Fungi of this disease survive on corn and many other grass species, so there are many host plants that can contribute to the level of this disease.

Unlike the other common ear rot diseases, however, Fusarium ear rot favors warm and dry conditions. Because of this tendency to favor warmer temperatures, an additional harvest management recommendation is to cool stored grain to below 50 degrees as soon as possible to slow the spread within the bin.

Cladosporium ear rot is identified by scattered kernels that have dark brown to green fuzzy mold which can cause random dark kernels to appear rotted with ruptured kernel caps. This ear rot is not associated with mycotoxins, so it only impacts grain quality and potential harvest dock due to lighter TW and kernel discoloration. Cladosporium ear rot is fairly common, but its true yield impact is limited.

Penicillium ear rot is identified by blue-green fungal growth usually found at the tip of the ear. This disease can also be associated with physical damage from birds and/or insects, which may occur to the tip of the ear. Mycotoxins and ochratoxins may occur with this disease and, at certain levels, can be toxic to mammals. High humidity is the biggest factor in disease development and spread of the rot.

Penicillium ear rot

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Submitted by Doug Kirkbride, Syngenta product development agronomy manager.

Photos are either the property of Syngenta or used under agreement.