Grain Sampling and Mycotoxin Testing – CPN-2003

Corn Disease Management

Grain Sampling and
Mycotoxin Testing

CPN 2003 — 2016

 If corn ear rots were a problem in the field, it is important to test harvested grain for mycotoxins. Obtaining a representative sample for mycotoxin testing is critical for accurate results. It’s also important to know that testing methods vary in accuracy. 

This publication recommends grain sampling and testing methods for detecting mycotoxins.

Figure 1. Several subsamples of corn are pooled to form a larger representative sample.

Figure 1. Several subsamples of corn are pooled to form a larger representative sample.

Sampling Requirements

The accuracy of a mycotoxin test result largely depends on the quality of the grain or silage sample. The USDA Grain Inspection Handbook and the Canadian Grain Commission recommend specific sampling methods to ensure that samples accurately represent the grain population. Sample collection methods vary depending on whether the sample is collected from the field (combine), a grain truck, a shipping container, or at the elevator or point of sale.

What does a representative sample consist of?

Although sampling methods vary, the size of the representative sample is consistent. According to the USDA Grain Inspection Handbook, a representative sample is at least 4.4 pounds, and preferably 5 pounds (2-2.5 kg). In many cases, several grain subsamples will be taken and then combined into a single composite sample (Figure 1).

The USDA Grain Inspection Handbook recommends that each subsample for the composite sample be at least 4.4 pounds (2 kg). Combine these subsamples to make a single composite sample. Mix the composite sample thoroughly, and then take a final 5-pound (2.5 kg metric) sample from the composite for further testing. 

Gather the subsamples several different times from a moving stream of grain while the grain is being loaded or unloaded. Sample probes are commonly used for stationary loads of grain.

Don't Rely on Appearance Alone

There are several technologies for testing mycotoxin concentrations in corn grain and silage. Never rely solely on visual methods such as the black light test (Figure 2). Visual test results can be inconsistent, so always test samples using recommended methods, or send them to professional laboratories. 

Figure 2. Fluorescence under a black light is not a useful way to determine if grain is contaminated with a mycotoxin.

Figure 2. Fluorescence under a black light is not a useful way to determine if grain is contaminated with a mycotoxin.


Testing Kits

Several companies sell kits that detect and measure specific mycotoxins. Using such kits will require an initial investment of several thousand dollars to purchase the proper testing equipment. However, once you have the equipment, the cost of testing a single grain sample (a subsample of a larger sample) for one particular mycotoxin is usually less than $10 (Figure 3).

Companies that sell mycotoxin detection equipment and test kits include:

Professional Laboratories 

Local laboratories and grain inspection services may test individual corn samples for mycotoxins. Below is an incomplete list of select grain testing providers. Check with your local Extension office for a more complete list of grain testing facilities in your area. For a list of labs in Ontario, visit Costs and sample submission procedures vary by provider.

Find Out More

The Crop Protection Network (CPN) is a multi-state and international collaboration of university and provincial extension specialists, and public and private professionals that provide unbiased, research-based information to farmers and agricultural personnel. Our goal is to communicate relevant information that will help in the identification and management of field crop diseases.


Charles Woloshuk, Purdue University; Tom Allen, Mississippi State University; Martin Chilvers, Michigan State University; Travis Faske, University of Arkansas; Anna Freije, Purdue University; Tom Isakeit, Texas A&M University; Daren Mueller, Iowa State University; Trey Price, LSU AgCenter; Damon Smith, University of Wisconsin; Albert Tenuta, OMAFRA and Kiersten Wise, Purdue University


Gary Bergstrom, Cornell University; Alyssa Collins, Pennsylvania State University; Andrew Friskop, North Dakota State University; Doug Jardine, Kansas State University; Hillary Mehl, Virginia Tech University; Alison Robertson, Iowa State University and Adam Sisson, Iowa State University

Photo Credits

All photos were provided by and are the property of the authors and contributors except Figure 2 by John Obermeyer, Purdue University.


Funding for this project was provided by the United States Department of Agriculture National Institute for Food and Agriculture (USDA-NIFA) project Integrated Management Strategies for Aspergillus and Fusarium Ear Rots of Corn. NIFA Award Number: 2013-68004-20359. We also thank the Grain Farmers of Ontario for support.

Design and production by Iowa State University Extension and Outreach Agriculture and Natural Resources Communications Unit.


© 2016 by the Crop Protection Network. All rights reserved.
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