Inspecting for Stalk Rot and Ear Rot in Corn
You’ve probably heard a little bit about the problems related to stalk rots, but you may not know that stalk rot can often lead to ear rot. With corn harvest underway, ear rots are being reported across the Corn Belt, and it’s a good time to evaluate the corn grain going into farm storage.
Why are stalk rot and ear rot a problem in corn?
Stalk rot causes issues with corn stalk integrity which can cause additional issues with the plant:
premature death of corn plants
yield loss due to the kernel-fill period being shortened
stalk lodging caused by stalk cannibalization
secondary disease infections such as ear rots become common and can result in ear loss
These diseases can also cause harvest difficulty:
machine harvest requires the constant adjustment to separate lighter corn kernels from material passing through the combine
higher moisture at harvest may cause increased drying cost or dockage at delivery
risky grain storage due to molds and insect damage that may be involved
The most reliable method to control mycotoxins in stored grain is to dry corn to 13 percent moisture or less, and to monitor stored grain often.
What causes stalk rot and ear rot?
There are several fungi that cause stalk and ear rot:
Anthracnose stalk rot can be identified by black lesions on the outside of the corn stalk. Cloudy weather favors anthracnose development.
Gibberella and Fusarium stalk rots are similar in many ways. Both are identified by a pinkish pith material inside the corn stalk; both flourish in wet, warm environments following silking; both stalk rots can lead to ear rots, and are the most prominent in hailed or insect damaged ears (though they can be common in undamaged ears as well).
Gibberella and Fusarium ear rots display as white or pink mold areas on the corn ears; corn grain stored containing these molds run the risk of developing mycotoxins that can be poisonous when consumed by livestock.
Fusarium sometimes shows as a white powder on outside of corn stalks.
Gibberella can be seen as pepper spots on stalks.
Diplodia stalk rot and ear rot can be identified as very small brown specks on husks and ears. Diplodia ear rot generally develops at the base of corn ears as a gray or black mold. Diplodia does not develop mycotoxins.
Charcoal stalk rot dries the pith of the stalks and produces sclerocia that compares to charcoal dust. Charcoal stalk is usually the cause of premature death of corn plants.
Bacterial stalk rot appears as brown water soaked lesions accompanied by slimy roots.
Penicillium ear rots are blue-green in color and requires a wet environment to grow.
As with many diseases in corn, timing of stress to corn plants can also cause stalk rot incidence, as are temperature, moisture stress, seed genetics and fertility.
Identifying stalk rot and ear rot
Rather than identifying which stalk or ear rot fungi is present, locating a presence of rot can be more important for making harvest management decisions. As the 2018 corn crop is showing signs of maturity, with ears beginning to droop and plants losing their color, now is a good time to begin scouting for stalk and ear rot presence.
Examine each field in several locations by pinching stalks 1 to 2 nodes from the ground on 10 consecutive plants. If the pinch causes the stalk to collapse, it likely has some sort of stalk rot.
Take time to split the stalk open of the collapsed plants and examine the internal stalk contents. If the pithy area of the stalk has shrunk or become discolored, stalk rot is evident.
Another method of determining stalk rot incidence is to push corn plants to approximately to a 45 degree angle from the upright position. Select several locations using 10 to 20 consecutive plants. Plants that collapse from the pushing are probable stalk rot victims.
If 10-15 percent of plants indicate stalk rot presence from either scouting method, you should consider an early harvest. Target fields of highest stalk rot incidence for the first to be harvested.
This scouting should be done on a weekly basis until harvest.
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