Potential for Aflatoxin Peanut Notes No. 223 2022
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The hot and dry weather in August and early September has created an environment in some fields for potential issues with aflatoxin. Unlike the lower southeastern US where aflatoxin can be a major issue, we have often experienced limited amounts even when we have hot and dry conditions. The intensity of the heat in NC and Virginia is often lower than Georgia, Florida and Alabama. Aspergillus flavus, the mold we can find in the peanuts and other crops like corn, is fairly ubiquitous in soil and under cooler and moist conditions the pathogen is kept in check by other organisms. When it gets hot and dry, Aspergillus flavus can become dominant because it can handle these extremes better than other organisms it competes with or is suppressed by.
The mold will produce the toxin. This is a natural evolutionary process and is a defense strategy by Aspergillus flavus against other organisms. It turns out it can hurt people too. Aflatoxin is nothing to mess around with. It is a compound that accumulates in the liver, and over time causes major negative effects on humans and livestock, especially those with compromised immune systems or the very young or very old. We should not worry about the peanut products we consume having aflatoxin because we have a very good inspection system in place at the point of sale that will decrease the likelihood that we will consume aflatoxin in the foods we eat. However, there is a cost to the grower and sheller when peanuts have mold and aflatoxin.
When peanuts are sold and a samples is taken at the buying point, the NCDA&CS inspector not only grades peanuts (SMK, ELK, etc.) but they also look for Aspergillus flavus (the mold.) If a load has mold, the buyer is notified and the load is then evaluated even closer for the actual toxin (aflatoxin.) If the level is at 15 ppb or greater, the load cannot go into the commercial trade. It can be crushed for oil at a much lower price for the farmer. The farmer does have the option to take the peanuts back and blend with other peanuts to get the aflatoxin concentration lower, but this is not easily accomplished and it is possible to compromise even more loads.
The mold is most often associated with damage to pods and kernels, especially the loose shelled kernel fraction (LSKs.) Anything thing that increases entry of soil into the pod that contaminates the kernels will increase the potential for aflatoxin. Insect and nematode damage have been shown to increase risk to aflatoxin.
With all of this said, during the season there is no magic bullet to prevent mold from developing outside of irrigation. In NC, that occurs on about 15% of our acres. And it is really an unknown until the peanuts are harvested and taken to the buying point where inspection occurs and then on to the sheller for chemical analysis.
For farmers in areas where intense dry weather has been experienced, it will be good to keep the good peanuts and the drought-stressed peanuts separated if at all possible. For example, if you have a field that has a pivot and the irrigated peanuts look great but the edges around the pivot have been experiencing drought for a prolonged period of time, don’t harvest these together. The good peanuts could be compromised. A concentration of 15 ppb is very very low.
We may not have a major issue with aflatoxin in NC and Virginia, but the potential is there is some places. Just like with spider mites, the cooler temperatures this week and possibly next week, will help slow the mold down, as will some of the rain we received over the past weekend.
Even though Aspergillus flavus becomes dominant in fields during hot and dry weather (the biology of this pathogen allows it to survive when many other pathogens do not,) it can do really well under storage. It can explode, and that is why shellers are diligent about not putting loads with the mold in with good peanuts. Just like farmers, the manufacturers the shellers sell to have strict policies on what they buy relative to aflatoxin contamination. The sheller has to be careful about not creating the potential for a major aflatoxin issue in storage at on the post-harvest side of things.
Aspergillus flavus associated with seed (kernels from the previous year,) can be compromised when planted the next season. A good seed treatment can minimize the negative impact of the pathogen on stand establishment. This demonstrates that aflatoxin not only can impact the supply chain for the current peanut crop, but it can have ramifications on the peanut crop the following season.