Using Atoxigenics to Manage Aflatoxin
Aspergillus ear rot (caused by the fungus Aspergillus flavus) is one of the most economically important corn ear rots in the southern United States (Fig. 1). The fungus produces aflatoxin, which is a dangerous mycotoxin. Most governments regulate aflatoxin in food and feed, because it is harmful to humans and livestock.
One approach to managing aflatoxin involves using atoxigenics as a biocontrol strategy. This article describes how atoxigenics work and provides recommendations on when to use them.
How Atoxigenics Manage Aflatoxin
Biological control strategies to manage aflatoxin accumulation in corn utilize atoxigenic strains of A. flavus. Atoxigenics are naturally occurring strains of A. flavus that, as the name suggests, do not produce mycotoxins.
Atoxigenics can help reduce aflatoxin accumulation in corn and other at-risk crops, including peanuts, cottonseed, and pistachios. For corn, there are two atoxigenic strains of A. flavus labeled for use in the United States to prevent aflatoxin accumulation. They are sold under the trade names AF36 Prevail® and Afla-Guard®.
When applied to the crop, these atoxigenic strains are dormant and are carried on nonviable grain (either sterilized wheat or barley) (Fig. 2). The atoxigenic fungus activates with moisture and begins to produce spores, relying on the grain-carrier as food. The spores, which are dispersed by the wind eventually blow upward and colonize the kernels of the developing ear.
Atoxigenics may result in ear mold, but they have a minimal effect on kernel quality. The spores from the atoxigenic strains will outnumber the spores of native, toxin-producing A. flavus strains, and they will out-compete the native strains for the limited number of sites in the kernels where they can grow. This decreases the overall aflatoxin contamination of the crop.
Under some circumstances, applying atoxigenics increases the incidence of Aspergillus ear rot, usually at the tips of the ears (Fig. 3). However, this damage is greatly offset by the reduction in aflatoxin.
Applying atoxigenics is not without risks. Before using these products, always consider these factors.
It will take several days for the fungi in these products to activate and produce spores. It’s important to apply these products before the native, aflatoxin-producing strains infect corn. If you apply the atoxigenic strains too late, you will not reduce aflatoxin concentrations. Ideally, you want the atoxigenic strain to begin producing spores during silking (R1).
Too Little Moisture
Atoxigenics are living organisms and need a small amount of moisture to activate and produce spores to colonize ears. If you apply the atoxigenics under dry conditions, they may not produce many spores and, therefore, not be very effective.
Too Much Moisture
Conversely, if there is a heavy rain after you apply atoxigenics, it may bury much of the material in the soil, which renders it ineffective.
Do not carry over unused atoxigenics for the next season. Remember that these are living organisms, so storage conditions may decrease their viability. However, you can test the viability of these products by placing grains on a moist paper towel and sealing it in plastic bag. Viable atoxigenics will produce olive-green, moldy growth after three or four days (Fig. 4).
Fig. 4. Spores of A. flavus developing on grain during a viability test.
Who Should Use Atoxigenics?
Atoxigenic products add costs to corn production, so it is important to carefully weigh the efficacy and economic benefits of using these products before applying them.
If you live in areas where aflatoxin contamination is an annual threat, you should consider using atoxigenic products to reduce aflatoxin concentrations in your finished grain. Be aware that unless conditions are favorable for aflatoxin production (hot and dry conditions during grain fill, or extended periods of wet weather that delay harvest beyond physiological maturity), atoxigenic products may not provide an economic advantage.
If Aspergillus ear rot and aflatoxin are rarely a problem where you live, it is unlikely that you will need atoxigenic products.
In the United States, AF36 Prevail® can be applied between V7 and silking (Fig. 5); Afla-Guard® can be applied between V10-V11 and silking.
Always read and follow manufacturer labels when applying one of these products. These products may not be available in all regions. Contact your local Extension specialist to determine the availability, price, and recommended rates for atoxigenics in your area.
Authors and Reviewers
Tom Isakeit, Texas A&M University; Tom Allen, Mississippi State University; Martin Chilvers, Michigan State University; Travis Faske, University of Arkansas; Anna Freije, Purdue University; Daren Mueller, Iowa State University; Trey Price, LSU AgCenter; Damon Smith, University of Wisconsin; Albert Tenuta, OMAFRA; Kiersten Wise, Purdue University; Charles Woloshuk, Purdue University; Doug Jardine, Kansas State University; Hillary Mehl, Virginia Tech University; Alison Robertson, Iowa State University and Adam Sisson, Iowa State University
Images: J. Obermeyer, T. Isakeit, G. Shuster, and T. Faske