***Updated in 2025, this version replaces the previous 2016 Using Atoxigenics to Manage Alfatoxin publication.***

Aspergillus ear rot (caused by the fungus Aspergillus flavus) is one of the most economically important corn ear rots in the southern United States (Figure 1). The fungus that causes Aspergillus ear rot 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 is the application of atoxigenic (non-toxin-producing) strains of A. flavus as a biological control strategy. This publication describes how atoxigenic strains work and provides recommendations on when to use them.

How Atoxigenics Manage Aflatoxin

One method of biological control to reduce aflatoxin accumulation in the field uses atoxigenic strains of A. flavus. These atoxigenics are naturally-occurring strains of A. flavus that do not produce mycotoxins. Atoxigenics can help reduce aflatoxin accumulation in corn and other at-risk crops, including peanut, cottonseed, and pistachio. For corn, the products available in the U.S. are AF-36 Prevail™, AF-36 Prime, FourSure™, and Afla-Guard®.  FourSure™ consists of four different strains, while the other products consist of single strains. The products AF-36 Prime and Afla-Guard® are OMRI (Organic Materials Review Institute) listed for organic use. All atoxigenic products consist of the dormant fungal strain on non-viable grain (either sorghum or barley) (Figure 2). After application, in the presence of moisture or high humidity, the atoxigenic fungus grows and produces spores, relying on the grain-carrier as food. The spores are dispersed by wind throughout the field and eventually colonize the kernels of the developing ear.

Atoxigenics may result in ear mold, but they have a minimal effect on kernel quality, as most of the effective colonization is not visible to the eye. 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 colonize and grow. This exclusion of toxin-producing strains by the atoxigenic strains decreases the overall aflatoxin contamination of the crop.

Under some circumstances such as drought, applying atoxigenics may increase the incidence of Aspergillus ear rot, usually at the tips of the ears (Figure 3). However, this damage is greatly offset by the reduction in aflatoxin.

Potential Pitfalls

The success of applying atoxigenics for aflatoxin control depends upon several factors.

Timing

It will take several days for the fungi in atoxigenic products to break dormancy, grow and produce spores. It’s important to apply these products as early as possible, to have more of their spores available to colonize thecorn crop and outcompete the native, aflatoxin-producing strains. A delayed application of the atoxigenic strains may not be as effective in minimizing aflatoxin accumulation, compared with an earlier application. Ideally, the atoxigenic strains should be applied before silking (R1).

Too Little Moisture

The amount of spores produced by atoxigenics applied during dry seasons (e.g. drought) will be less than that produced under field conditions with more moisture. This might reduce effectiveness.

Too Much Moisture

Conversely, if there is a heavy rain after atoxigenic application, some of the product may be buried in soil. The product needs to be exposed to the atmosphere to be effective. In irrigated fields, the atoxigenics ideally should be applied after an irrigation.

Uniformity of Application

Apply atoxigenics uniformly to the field, do not apply in strips, as there may not be sufficient or timely coverage of corn in the middle of non-treated strips.

Storage

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 a plastic bag. Viable atoxigenics will produce olive-green, moldy growth after three or four days (Figure 4).

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 farm where aflatoxin contamination is an annual threat, and especially if you have had a history of contamination, consider using atoxigenic products to reduce aflatoxin concentrations. 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. You should think of the application as a protectant against contamination.

If Aspergillus ear rot and aflatoxin are rarely a problem where you live, it is unlikely that you will need atoxigenic products.

Application Timing

In the U.S., FourSure™ is labeled for application from V5 to tassel (VT). AF-36 Prevail™, AF-36 Prime, and Afla-Guard® are labeled for application from V7 to silking (R1; Figure 5).

Always read and follow manufacturer labels when applying atoxigenic 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.

Acknowledgements

Authors

Tom Isakeit, Texas A&M University; Tom Allen, Mississippi State University; Martin Chilvers, Michigan State University; Travis Faske, University of Arkansas; Daren Mueller, Iowa State University; Trey Price, LSU AgCenter; Damon Smith, University of Wisconsin-Madison; Albert Tenuta, OMAFRA; and Kiersten Wise, University of Kentucky.

Reviewers

Doug Jardine, Kansas State University; Hillary Mehl, Virginia Tech University; Alison Robertson, Iowa State University; and Adam Sisson, Iowa State University.

Sponsors

Funding for this project was provided by the United States Department of Agriculture National Institute for Food and Agriculture (USDA-NIFA) project Integrated Management Strategies for Aspergillus and Fusarium Ear Rots of Corn. NIFA Award Number: 2013-68004-20359. We also thank the Grain Farmers of Ontario for support.