Aspergillus rot symptoms in corn ear and kernels.
Tips to help reduce the levels of aflatoxin in corn.
By Paul E. Sumner, University of Georgia
Prior to Harvest
Sanitation of equipment is the first step in preventing post-harvest aflatoxin contamination.
- Clean out all harvesting, handling and drying equipment and storage bins prior to harvest.
- Remove all broken corn, dust and foreign material that can provide a source of contamination.
- Check and repair storage bins to prevent moisture leaks from faulty joints or other problems.
- Clean bins and remove debris to reduce contamination. Use an approved insecticide to treat the bin before filling.
- Mow around storage bins to discourage insect/rodent activity.
- Always remember to provide adequate dust protection for those who work around grain-handling equipment.
The following practices will reduce the likelihood of this problem.
- When corn reaches maturity, harvest immediately and dry mechanically.
- Harvest should begin when the moisture level reaches 28 to 30 percent. Studies have shown that most corn hybrids will normally lose about 0.5 to 0.6 percent moisture per day during the dry-down period. You can reduce field exposure by at least 1 to 2½ weeks by harvesting above 22 percent moisture compared to letting corn dry in the field to 15 percent or less. This will require immediate drying, however.
- Irrigated corn generally has fewer problems with Aspergillus infection due to better growing conditions (less drought and heat stress, etc.). If corn is irrigated, harvest the crop outside the pivot separately and store it separately to reduce chances of contaminating good corn. Be sure the clean the combine before harvesting the irrigated corn.
- Set combines to minimize grain damage.
- Set fans higher to clean out light-weight cracked grain and undeveloped kernels.
- Slowing header seed reduces kernel damage.
- Ears in contact with the ground for some time usually exhibit higher than normal aflatoxin levels and should not be picked up, if possible.
- Combine cylinder/rotor speed should be slow enough and concave clearance as great as possible to provide adequate threshing. Less damage to seed coat occurs with these settings.
- Install filler plates between cylinder bars to reduce physical damage.
Proper grain handling
- Do not hold high moisture grain in wagons or trucks longer than 6 hours.
- Place high moisture corn being held for drying in a holding bin using forced air to keep it as cool as possible.
- Use sound sanitation practices in handling grain. Clean augur wells and pits, and clean around dump stations before and after each use.
- Minimize physical damage by conveyors or from dropping the grain into tall bins.
Proper grain storage
Grain held in storage should be inspected and probed every 3 to 4 weeks. Check for insect activity, high temperatures, mold growth or sprouting at the top of the grain. Drying temperature and drying time may have an effect on the development of aflatoxin in stored grain. Slow drying with low heat over long periods could promote aflatoxin development.
Drying corn in deep layers can produce conditions highly favorable for mold development. The drying temperature for this method is increased only 10 to 20 degrees F above outside conditions. The relative humidity in the top layer of grain remains very high for an extended period of time. These factors are favorable for aflatoxin production.
A lot of grain is batch dried in bins. Wet grain is usually placed about 3 to 4 feet deep in a drying bin and hot air (about 140 degrees F) is forced through the grain, drying the batch normally in less than 24 hours. The grain is then cooled for storage in the same bin or moved to a storage bin and cooled by aeration fans.
Aflatoxin production in column dryers operated at high temperatures (180-200 degrees F) and short drying time (1-2 hours) is very unlikely. This is true for batch or continuous flow column type dryers.
Several organic acids are registered for use on high moisture corn. Most grain can find a safe and legitimate use, however. Cleaning grain by screening or a gravity table can reduce aflatoxin concentrations by removing the most heavily contaminated particles. This can be expensive, however, and it is not possible to predict just how much the aflatoxins will be reduced.
Editor's Note: This is a portion of a larger research publication from the University of Georgia College of Agriculture & Environmental Sciences. Click here to view the entire document.