Grainnet

Mycotoxins Detected in Indiana Corn

By Charles Woloshuk, Department of Botany and Plant Biology, Purdue University

In terms of mycotoxin levels, this year’s Indiana corn crop is the worst that I have seen in more than 10 years.

Every year since 1989, we have conducted a survey of the Indiana corn crop just prior to harvest to determine whether ear rots and the associated mycotoxins are an issue for concern.

For the survey, the field staff of the Indiana Statistics Service collects two samples of five ears from each of their field plots around the state.

The samples are sent to Purdue University for evaluation of ear rots and mycotoxins.

This year, 316 samples from 70 counties were examined to determine the severity of the major ear rot diseases.

Twenty samples with significant amounts of Fusarium ear rot, Gibberella ear rot, or Aspergillus ear rot were selected for mycotoxin analysis (aflatoxin, ochratoxin, zearalenone, deoxynivalenol, and fumonisin).

The toxicology group at the Indiana Animal Disease Diagnostic Laboratory performed the analysis.

DON and fumonisin levels are a concern

A striking observation this year was the number of samples containing at least one ear with Gibberella ear rot. This was remarkable because we seldom have seen the disease in the survey over the past 10 years.

Symptoms of Gibberella ear rot are pinkish-red fungal growth that usually begins at the tip of an ear and progresses toward the base.

This ear rot is favored by cool, rainy weather, especially during the first 21 days after silking. This year, the disease ranged from a few rows of kernels to about 25 percent of the ear.

Samples from six counties were found to contain deoxynivalenol, also known as DON or vomitoxin, ranging from 0.5 to 8 parts per million (ppm).

These levels should be of greatest concern to the swine producer. Swine are more sensitive to DON than ruminant animals and poultry. Signs of DON mycotoxicoses in swine can include feed refusal, vomiting, diarrhea, and reduced feed consumption.

A second striking observation this year was the high concentrations of fumonisin. Fumonisins are produced by the pathogen causing Fusarium ear rot.

The disease is most severe when earworms and other insects damage ears. Samples from eight counties contained fumonisin B1 ranging from 0.7 to 174 ppm.

Five of the samples contained greater than 18 ppm. These levels of fumonisin are well above the amounts that can cause leucoencephalomalacia in horses and pulmonary edema in swine.

Although we did not observe Aspergillus ear rot disease symptoms, aflatoxin was detected in one sample. One of the ears in this sample was barren.

The remaining ears were very small, poorly pollinated, and severely damaged by insects. The kernels also had severe Fusarium ear rot symptoms. Mycotoxin analysis found 10 parts per billion (ppb) aflatoxin and 9 ppm fumonisin B1.

Diplodia ear rot has become a real nuisance to Indiana corn producers. Although the disease is not associated with mycotoxins, the rot can reduce test weight and predispose kernels to invasion by other fungi during storage.

Seven percent of the samples had at least one ear with Diplodia ear rot, which is similar to previous years. However, the disease appears to be more widespread across the state, with samples from 21 counties having the disease.

What to do?

Removing mycotoxin-contaminated kernels is an arduous task. Severely infected kernels, which often contain most of the mycotoxin, can be removed by cleaning the grain.

Diseased kernels will also easily break during handling, increasing the amount of fine material in a storage bin.

These fines will decrease airflow during aeration, which will increase the potential for spoilage. If possible, pre-cleaning — especially after drying and before delivery and/or storage — is highly recommended.

This will help to minimize discounts and improve storability of the corn.

Proper storage of grain is crucial. Drying the infected grain to below 15 percent moisture will stop further growth of the mycotoxin-producing fungi.

However, the diseases compromise kernel integrity. As a result, storage fungi — which can grow at 14 percent to 15 percent moisture — will find it easy to invade the kernels and cause further spoilage damage and self-heating.

Therefore, corn should be dried to below 14 percent moisture and cooled to below 50° F as soon as possible, and then to 30° F for winter storage.

Storage time should be limited to the cold weather season; no infected corn should be held into next summer.

The diversion of corn to ethanol production raises the possibility that mycotoxin-contaminated grain usage may result in contaminated distiller’s dry grain (DDG).

A number of sources have stated that mycotoxins are concentrated in DDG to as much as three times that of the original contaminated grain.

To determine if mycotoxins are present, suspect corn or DDG needs to be analyzed with one of a variety of methods.

More information about ear rot diseases, mycotoxins, and grain storage is online at http://www.btny.purdue.edu/NC129/.

For more information, contact Charles Woloshuk, Department of Botany and Plant Pathology, woloshuk@purdue.edu.