Moldy grain and vomitoxin levels vary considerably within the grain lot. This is largely because the number of ears infected with Gibberella zeae, the fungus that causes Gibberella ear rot and produces vomitoxin in the grain, and number of infected kernels on a given ear within a field are highly variable. In addition, ears, and kernels with a similar appearance in terms of surface moldiness may have vastly different levels of internal fungal colonization, and consequently, different levels of vomitoxin contamination. In addition, pockets of warm, humid area in the grain lot coupled with moldy grain may lead to vomitoxin “hot spots” that can affect vomitoxin test results if sampling is inadequate. This may lead to price discounts or rejection of grain lots that are less contaminated than test results suggest, or conversely, acceptance of lots that are more contaminated than indicated by the results. For instance, if a single sample is drawn and the location from which it is drawn happens to be a hot-spot, then the overall level of contamination of the lot will be overestimated. Conversely, if the sample misses the hot spots completely, vomitoxin contamination may be underestimated. A single sample is never sufficient when testing grain for vomitoxin or other mycotoxins.
Accurate testing depends on thorough and appropriate sampling and sample processing. Guidelines for grain sampling, based on research with scabby wheat and barley, are available from the United States Dept. of Agriculture Grain Inspection, Packers and Stockyards Administration (GIPSA). To collect a representative grain sample, 5-10 samples should be randomly collected from multiple locations in the bin or truckload. Samples taken only from the bottom, central or outer portions of the load or from the beginning and end of the grain stream will not provide an accurate estimate of toxin contamination of the lot. This is largely because lightweight, heavily contaminated kernels often end at the top of the pile/load and contaminated fines and dust settle at the bottom during transport and other forms of grain movement. For end-gate sampling, samples should be drawn from the entire width and depth of the grain stream. For sampling with hand or mechanical probes, multiple samples should be drawn from throughout the bin or truck, along an “X”-shaped pattern, for example. Once samples are obtained, bulked, and cleaned, the grain must be thoroughly mixed and ground uniformly, in a clean grinder, to resemble flour. Finer particle size increases surface area of the grain and enables efficient extraction of vomitoxin.
Source: modified from the following factsheet: https://ohioline.osu.edu/factsheet/plpath-cer-04.