Storage Mold: Precautions to Avoid Grain Spoilage During Storage

 

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.

 

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

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.

 

 

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).