Aflatoxin and Storage Recommendations for Infected Grain
By Shelly Kerns, Boyd Padgett, Trey Price
LSU AgCenter
There has been an abundance of ear rots reported in Louisiana throughout this growing season. As the harvest window is winding down, and with many growers already finished with harvest, I have heard of one reoccurring issue in particular: aflatoxin. There have been reports of heavy docking and even loads being rejected at the elevators. In addition to this, there are now many growers who are planning to store their grain who have been inquiring about storage guidelines for infected grain. Overall, there have been many questions about why aflatoxin levels have been so high this year. Below is a summary of aflatoxin development/production and recommendations for storing infected grain.
Mycotoxin Development
Aflatoxin is a mycotoxin, meaning that it is a toxic chemical produced by fungi. Aflatoxin can only be produced by two species of Aspergillus that are plant pathogenic (A. flavus and A. parasiticus). Aspergillus primarily presents in infected corn plants as an ear rot pathogen. Ears with Aspergillus ear rot will exhibit as a fuzzy or felt-like olive-green mold (image 1). It is important to note that just because an ear is infected does not mean the fungus will produce aflatoxin. It is only when corn plants enter severe stress that the fungal pathogen can be triggered to start producing the mycotoxin. Aflatoxin production is historically associated with high heat, severe drought, and high humidity. Our growing season had a substantial wet period, and because of this, there has been confusion on why aflatoxin presence has been so bad this year. Aspergillus overwinters in the soil. Rainfall created the perfect environment for spread of fungal spores. Raindrops can splash spores from soil to plants within a field, and wind can also pick up spores and disperse them further. Once the rainfall subsided, spores were most likely able to start germinating and infecting plants. Aspergillus spores can infect through the silks during the late silking stage, or through wounds caused by physical environmental injury or insect feeding. As the season progressed and the weather became extremely dry, this probably triggered Aspergillus to start producing aflatoxin.
Management Practices to Mitigate Aflatoxin Production
• Plant hybrids with good earworm resistance. Aflatoxin is more likely to develop in ears and kernels damaged by insect feeding. • Consider biological applications. There are biological products such as Afla-Guard, F36 Prevail™ / AF-36 Prime, and FourSure that can be applied from mid vegetative stages up until silking. Application of these products should be prioritized on non-irrigated fields. More information about how these products work can be found here: https://cropprotectionnetwork.org/publications/using-atoxigenics-to-manage-aflatoxin • Plant drought resistant hybrids when possible. Especially if planting corn behind corn in a field that has a history of ear rots. Irrigate when feasible. • Rotate crops. Crop rotation to a non-host crop such as soybean can help reduce the amount of Aspergillus inoculum in soil between growing seasons. • Till the soil. Tillage physically breaks up and buries infected crops residue. This slows down fungal spore production.
Harvest and Storage Recommendations
• Consider harvesting irrigated fields separately from non-irrigated fields when possible, prioritizing irrigated fields first. Cross contamination can occur from leftover grain in trucks, holding bins, and drying facilities. • Adjust your combine settings. If you know you will be harvesting a field with substantial kernel damage, adjust the cylindrical speed and fan airflow to filter out damaged kernels. • Rapidly dry grain that you are planning to store. It is recommended to dry down infected grain within 24-48 hours after harvest. To prevent the spread of Aspergillus growth and further aflatoxin development, the grain should be dried between 14-13% moisture for long term storage. • Keep stored grain cool. Storage temperatures below 55 degrees Fahrenheit are ideal. Also aerate the grain if storing in bins. This helps prevent moisture condensation which is conducive for fungal growth.