Early-season damage leads to potential for ear rots

TAGS: Crop Disease
Tom J. Bechman ear of corn showing some type of rot
UNWELCOME SIGHT: While no disease diagnosis was confirmed here, this ear was found in an area where many corn plants were damaged by wildlife feeding earlier in the season.
Corn Watch: Feeding by wildlife or mechanical damage can set up plants for ear rots later.

The woods along one side of the Corn Watch ’20 field provided fodder for many stories this year. Wildlife coming out of the woods, including deer and racoons, fed on leaves, stalks and eventually ears, besides knocking over stalks during their ventures into the field. Evidence of damage extended at least 150 feet into the field.

“When plants are damaged by wildlife feeding, birds or mechanical damage, it can set them up for disease organisms to invade,” notes Dave Nanda, director of genetics for Seed Genetics Direct, sponsor of Corn Watch ’20. “There is typically plenty of inoculum from a variety of diseases in the soil, which can cause problems when given the opportunity.”

Related: Nutrient deficiencies late in season may not matter
 

Ear rots and stalk rots were the major diseases that showed up late, Nanda says. Most of the disease he found just before harvest was primarily on stalks or ears that were injured earlier, or on ears where birds had pecked through husks and exposed the ear to invading organisms.

Here’s a summary of what Nanda found in the field:

Smut. According to the Purdue University Corn & Soybean Field Guide, smut, caused by a fungus, most often shows up on wounded plants at pollination and silking time. However, the fungus can also enter through silks to cause the disease.

“It’s quite obvious, because the silvery galls filled with black spores that form instead of ears are ugly,” Nanda says. “There were so many in a few areas where deer fed earlier in the summer that I called it a ‘smut garden.’”

Fortunately, only a small number of plants overall were infected, and the damage looks much worse than it is. It’s rarely of economic importance, Nanda notes.

Stalk rots. Stalk rots show up near the end of the season, even when stalks are damaged, Nanda says. “Anthracnose is the most common, and the one that concerns us most,” he says. “When weather conditions are right, it can spread in susceptible hybrids even in plants that aren’t injured.”

As the Purdue guide notes, anthracnose is characterized by stalk lesions that are shiny black and can extend through the rind into the pith. “It often looks like shoe polish,” Nanda says. “If this one takes off, it can spread quickly. Fields with many stalks failing a pinch or push test for stalk rot should be marked to be harvested as soon as possible.”

Tom J. Bechmanear of corn showing 3 types of rot


EAR ROT JACKPOT: This ear has two distinctive types of ear rot, and perhaps a third. Dave Nanda suspects the reddish kernels represent gibberella ear rot, the greenish kernels might be aspergillus, and the whitish discoloration in damaged kernels on the bottom of the ear could be diplodia in the making. These diseases were not confirmed.

Ear rots. Nanda found at least two ear rots and possibly three on one ear in the Corn Watch ’20 field just before harvest where wildlife damage occurred earlier in the year. He is confident that he found aspergillus, diplodia and gibberella in the field, although only on a small number of ears.

Two of the three, aspergillus and gibberella, can produce mycotoxins. Aspergillus is usually favored by dry conditions. However, just because the fungus is present and produces disease symptoms doesn’t mean it’s producing mycotoxins, experts say. That requires testing of the grain to look for mycotoxins. Some are harmful to humans and livestock.

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