Corn

How can I reduce aflatoxin level during harvest?

Mississippi corn producers sometimes have harvested corn rejected at grain elevators because of high aflatoxin levels. Aflatoxin is a chemical by-product of the growth of the fungus Aspergillus flavus on corn kernels. Aflatoxin may be harmful to animals which ingest contaminated corn. What level of aflatoxin is harmful?

Several different management practices may be utilized to minimize aflatoxin levels during the harvesting process. However, few if any practices are available which can rectify contaminated grain once it is collected. Thus, it is strongly recommended to utilize these practices during the harvest, handling and storage processes.

Don't delay harvest - Delaying harvest until grain moisture drops below 15% moisture will not reduce aflatoxin level. Conversely, harvest timing directly influences the duration corn is subjected to warm (above 80º F), humid (60-70% relative humidity) conditions which are likely to promote aflatoxin development. Thus, we generally recommend prompt harvest in order to avoid continued aflatoxin development, despite moisture dockage incurred. However, aflatoxin levels may escalate within a few hours if high moisture grain is not handled properly. Wet grain should be immediately dried to below 15% moisture or hauled to an elevator (which will dry the grain). Wet grain should not be stored in trucks, combines, bins or any non-aerated site more than 4-6 hours before beginning drying. These conditions are critical to grain quality because, the fungal growth which causes aflatoxin will escalate to excessive levels very quickly under these conditions. Conversely, the fungal growth approaches dormant levels when grain moisture drops below 15%.

Avoid bad areas - Separately harvest obviously stressed, stunted or damaged areas and field edges, if you suspect any aflatoxin problem. These areas are much more likely to contain high levels of aflatoxin. Producers can often benefit from aflatoxin sampling parts of fields. Producers may chemically test grain for aflatoxin content by submitting samples to the MSU State Chemical Laboratory (662-325-3324). Samples cost $35 each. Growers may also purchase aflatoxin test kits from various laboratory supply retailers including:

Clean grain - Fungal infection is more likely in shriveled, cracked kernels and foreign material. Thus, grain quality may be significantly improved by reducing the combine ground speed, increasing fan speed and opening sieves, so that these sources of contamination are removed from the sample. A postharvest mechanical cleaner or gravity separator may also help reduce moderate aflatoxin levels (50 to 100 ppb) below the FDA standard (20 ppb).

Sanitize equipment - Fungal infection can occur during storage as well as in the field. Thus, sanitation of handling and storage facilities is very important. Spores from fungi on infected grain readily disperse during handling and contaminate unaffected grain. Remove corn and debris remaining in combines, trucks, grain carts, pits, augers, bins, elevators, etc... on a daily basis. Chlorine cleaning solution (3/4 cup bleach per gallon of water) kills fungal growth when cleaning handling facilities. However, since chlorine solution is very corrosive, thoroughly wash with water after cleaning.

Related Publications: