Questions and Answers on Moldy Grain and Mycotoxins Part 2 Handling Corn in Storage

1. Harvest at the correct moisture and adjust harvest equipment to minimize damage to kernels. Mold and mycotoxins tend to be higher in (machine or insect) damaged kernels.

2. Dry harvested grain to 15% moisture and below (less than 13% moisture) to prevent further mold development in storage.

3. Store dried grain at cool temperatures (36 to 44oF) in clean, dry bins. Moderate to high temperatures are favorable for fungal growth and toxin production.

4. Periodically check grain for mold, insects, and temperature.

5. If mold is found, send a grain sample for a mycotoxin analysis to determine if toxins are present and at what level. For more on moldy grain, mycotoxins, and mycotoxins sampling and analysis visit the following website: http://www.oardc.ohio-state.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htm

Q6. Can Toxin levels increase while the grain is in storage?

Yes, toxin levels can certainly increase in storage if storage conditions are inadequate. If there are warm, moist areas/pockets in the grain lot, mold will continue to develop, causing the grain to deteriorate further and toxin levels to increase. Aeration is important to keep the grain dry and cool, and if not done appropriately, pockets of warm, damp areas will develop due to the metabolic activity of the grain and microorganisms.

The grain is still alive and as such is still respiring, and two of the end products of respiration are water and heat, exactly what the fungus needs to grow and produce toxin. In addition, kernels close to the walls of the silo tend to be at a lower temperature than kernels towards the center and the exchange of warm air from the center with cool air from the top or sides of the silo may lead to further moisture build up (due to condensation). However, it should be noted that while cool temperatures, air circulation, and low moisture levels will minimize fungal growth and toxin production, these will not decrease the level of toxin that was already present going into storage. Vomitoxin is very stable and will not be reduced with drying.

Variability stems from the fact that there is variation in the number of ears infected within a field and, on any given ear, there is variation in the number of kernels infected. Furthermore, kernels with similar appearance in terms of moldiness on the surface, may have different levels of internal fungal colonization and consequently variation in mycotoxin contamination. In addition, healthy-looking kernels may also be contaminated with vomitoxin. Variability is a major issue!! Because of this variability, sampling needs to be done correctly in order to adequately determine the level of contamination. There are always “hot spots” within the grain lot and if you sample only once or a few times and end up doing so in those “hot spots” then you’ll overestimate how contaminated the grain lot really is. Conversely, if you totally miss the hot spots then you’ll underestimate contamination. That’s the reason why we always recommend that multiple samples be taken from multiple locations within the lot, then bulk, mix and grind the grain before analysis.

We have not used all of the testing equipments that are out there, but most of the highly recommend ones are fairly reliable and consistent. The kits that give you quantitative estimates (1,2,3,15.4,38.4 ppm) are generally better that the semi quantitative (more than 5 ppm) or qualitative (yes/no response) kits… but it all depends on what you are using the kit for. In general, the ELISA kits (most of the kits that are out there are ELISA-based) are calibrated against the more sophisticated quantitative lab equipment, and if used correctly (incorrect use is another potential source of variation) should provide consistent results across elevators. However, test results from one elevator to another are also subject to variation in how the samples were drawn from one elevator to another. Unless the sampling is done correctly and in the same or a similar manner among elevators, it will be impossible to tell whether the differences (0 at one elevator and 10 at another) are due to differences among the testing equipments or to poor and inconsistent sampling protocols among elevators. In fact, the best way (but probably not the most practical) to compare elevators it to send subsamples from the same bulk sample for testing at the different elevators.

 Very moldy kernels are usually lighter than healthy, plump kernels, however, as was said in the paragraph above, plump-looking kernels may also be contaminated with vomitoxin. Any method that can be used to remove moldy kernels will help to reduce the overall level of contamination of the lot… moldy kernels are always more contaminated that the most contaminated of the healthy-looking kernels.