Storage Mold: Precautions to Avoid Grain Spoilage During Storage Back »

Written collaboratively by Emmanuel Byamukama and Connie Strunk.

Harvesting of corn and soybean is underway and/or will soon be starting throughout the state. Growers need to be aware of storage mold which can spoil the grain during storage. This is especially important for those who are storing their grain for longer periods of time as part of their grain marketing strategy.

The main pathogens responsible for seed spoilage during storage are fungal pathogens and these can be grouped into two types: i) field fungi and ii) storage fungi. Field fungi are those which infect grain in the field and require higher grain moisture content (>20%) for infection to take place. During storage when moisture content is low, these fungi are not active. Storage fungi; on the other hand, may contaminate the seed and do not usually invade the seed in the field but instead develop on the seed in storage under optimum conditions. Storage fungi spoil the grain by reducing dry matter content, rotting the seed, and lowering nutritional quality and some of these fungi may also produce mycotoxins which are poisonous when consumed either by livestock or humans.

Risk Factors for Mold Development During Storage

A number of factors increase the risk for storage mold to develop. These include:

  • Presence of inoculum on the grain before storage
  • Initial grain moisture content and moisture content throughout storage period
  • Impurities in the grain such as weed seed, insects, broken seed, plant debris
  • Storage temperature
  • Storage length

Storage fungi are ubiquitous and may contaminate the seed during harvesting, transportation, bin loading or during storage. However, grain that has already been invaded by field fungi is likely to deteriorate faster if proper storage conditions are not followed. The main risk factor for storage fungi to develop is grain moisture content at time of harvest and during storage. Fungal pathogens require a minimum amount of moisture in order to germinate and invade the grain. When the moisture level is below this threshold (varies with different pathogens, Table 1), the pathogen propagule remain on the seed surface without causing any damage. Moisture in stored grain may also increase due to leaks in the storage bins or from moisture resulting from convention currents. Active insects in the grain, in addition to, breaking the physical barrier for pathogens to initiate infection also increase temperature and moisture in the stored grain through their feeding and respiration. Impurities such as weed seed increase the risk of storage mold because these contain high moisture content and may provide an initial infection point. Broken seeds, as well as, insect carcasses such as dead grasshoppers may also provide the moisture needed for infection initiation.

Table 1. Moisture content in grain for fungal growth and mycotoxin production of storage fungi for cereal grain.
Fungal species Mycotoxin
produced
Moisture content (%)
for mycotoxin production
Moisture content (%)
for fungal growth
Aspergillus flavus Aflatoxin B1 17.6-19 19.2
Aspergillus parasiticus Aflatoxin B1 19 20.2
Aspergillus ochraceus Okratoxin A 16.5 19.6
Penicillium patulum Patulin 18 27
Penicillium exapansum Patulin 18.3-19 30
Penicillium aurantiogriseum Okratoxin A 18.5-19.6 20.2-22.0
Penicillium verrucosum Ochratoxin A 18 18.8-19.8
Fusarium proliferatum Fumonisin B1 20.5 25
Fusarium verticilliodes Fumonisin B1 20.5 25
Summarized from Magan et al 2003.

 

Temperature and length of storage can also influence the development of storage fungi. Grain stored below 50 F will have a lower tendency to develop storage fungi. At higher temperatures in the storage bin, fungal pathogens become more active. Similarly, the length of time when grain is in storage influences the extent of storage fungi development. Grain with a high moisture content can be stored safely for a few weeks before processing. However, such grain would quickly deteriorate if stored at a high moisture content for a longer period of time (months).

Management

  • Prevention of storage mold by monitoring pre-harvest and post-harvest grain moisture content is the best way to manage storage fungi. For recommended moisture content at harvest and options for drying grain, refer to Grain Storage: It Starts With Harvest. Recommended moisture content for soybean grain storage to limit storage mold growth is <12% and <13% for corn.
  • Grain should be cleaned to ensure the grain is free of broken seeds, plant debris, insect carcasses, and other foreign material.
  • Ensure grain bins and handling systems are clean to limit introducing debris and old grain that may have high moisture content.
  • Storage insects and rodents should be managed in order to avoid injury to the grain, and the temperature and moisture content should be monitored to observe if a change occurs such as a rise in temperature or moisture content as a result of the pests’ feeding and respiration. See How do I Manage Insects in my Stored Grain?
  • Monitor temperature and grain crusting during storage. Aerate grain periodically and equalize temperature throughout the grain mass in the storage facility.

References:

  • Munkvold, G. and White G. Compendium of Corn Diseases. 4th edition. APS Press.
  • Magan, N., Hope, R., Cairns, V., Aldred, D., 2003. Post-harvest fungal ecology: impact of fungal growth and mycotoxin accumulation in stored grain. In: Xu, Xiangming, Bailey, J.A., Cooke, B.M. (Eds.). Epidemiology of mycotoxin producing fungi. COST Action 835 Report, European Journal of Plant Pathology vol. 109, pp. 723e730.
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