What is Aflatoxin…Aflatoxin is a toxin produced by Aspergillus flavus, a fungus that is common in agricultural soils in Arkansas. If conditions are right, the fungus will attack corn plants, specifically corn kernels, to cause disease. The greatest concern about the disease (known as Aspergillus ear rot) is the presence of aflatoxin in infected corn kernels. Consumption of aflatoxin is harmful to humans and animals, and thus aflatoxin levels in corn are regulated by the U.S. government (Table 1). Very low levels of aflatoxin cause concern among grain buyers and processors.
There are several common kernel-rotting fungi found in Arkansas corn, but of these, only Aspergillus flavus produces aflatoxin. With a little practice, Aspergillus flavus can be visually distinguished from other kernel-rotting fungi. Aspergillus flavus is olive green and velvety (Figure 2). Affected kernels may be scattered on the ear, or a high percentage of kernels can be affected (Figure 3). Close inspection with a hand-lens or magnifying glass will reveal the distinctive, spore-bearing structures of Aspergillus flavus that resemble a globe supported on a slender stem (Figure 4).
Aflatoxin Pocket Guide…The Arkansas Corn and Sorghum Promotion Board, the Arkansas Cooperative Extension Service, and the University of Arkansas prepared a pocket reference for aflatoxin management.
Aflatoxin Presentation…Dr. Burt Bluhm of the University of Arkansas gave a great overview of the management practices as well as reseach being done to prevent Aflatoxin at the 2012 Producer Conference.
Management practices for Aflatoxin…Current management recommendations to minimize the impact of aflatoxin in Arkansas corn production can be divided into four major categories:
1. Hybrid selection. While yield is always a primary consideration, other hybrid properties should be taken into account. Genetic resistance specifically to aflatoxin accumulation is not available in commercial hybrids, and resistance to other corn diseases (such as Northern corn leaf blight and gray leaf spot) is not effective against Aspergillus ear rot. Therefore, selecting hybrids with resistance to a broad range of environmental stresses is recommended to minimize aflatoxin in Arkansas growing conditions. Select locally/regionally adapted hybrids with resistance to drought, insects, and stalk rots (good standability). Other considerations include strong emergence/seedling vigor, good grain drydown characteristics, and husk coverage. Information about the performance of selected hybrids in Arkansas is available from the University of Arkansas Variety Testing Program (www.arkansasvarietytesting.com).
2. Plant health. Healthy corn has the greatest chance of being aflatoxin-free corn. Planting early (but not too early) helps corn avoid some of the heat and drought stress that often comes with Arkansas summers and promotes aflatoxin. Maintain adequate soil moisture – drought stress before silking can weaken resistance against Aspergillus flavus. It is also important to maintain good soil fertility and manage insects.
3. Pre-harvest decisions. There are no commercially available fungicides that are effective against Aspergillus ear rot. However, a relatively new biological control product named Afla-Guard can provide some control of aflatoxin in Arkansas corn. The product contains a strain of Aspergillus flavus that cannot produce aflatoxin, but otherwise can infect corn. Applying Afla-Guard gives the non-toxic Aspergillus flavus strain a chance to out-compete the naturally-occurring, toxin-producing strains. Afla-Guard should be applied at V10-V12 to give the product time to become active during grain fill. It is important to note that while Afla-Guard can help reduce aflatoxin in some situations, it will not “cure” the disease or eliminate the toxin.
Afla-Guard – Is it right for you
- Good potential but will not eliminate aflatoxin –gives a 60 to 75% reduction at best
Cannot take a high risk field and make it low risk
- For example: a dry land field with 2000 ppb potential of Aflatoxin would only be reduced to 500 ppb with 75% control
More effective in reducing aflatoxin in fields with light to moderate risk -- 20 to 100 ppb for human consumption
Fields with some fertility and watering issues in extreme years
- Loose shuck cover
- Susceptible to disease and insects
- Dry land fields in years with stress --- drought, high heat
- Fields with some fertility and watering issues in extreme years
- Stress, especially heat/drought before tasseling
- Not practical or economical for highly productive fields where fertility and water is not an issue
Whether using Afla-Guard or not, be alert to stressed areas within a field such as dry corners of pivots, areas that did not get enough water, or other stresses. If fields have not been treated with Afla-Guard, they can be scouted to look for the presence of Aspergillus flavus before harvest. Areas of a field with high levels of Aspergillus ear rot are extremely suspect to have high levels of aflatoxin and should be handled separately from good corn (see below). Note: In fields treated with Afla-Guard, it is impossible to distinguish by eye the toxin-producing strains from the non-toxic strains.
4. Harvest & storage. When harvesting, separate healthy corn from corn at higher risk for aflatoxin. For example, harvest dryland or otherwise stressed corn separately from irrigated and less stressed corn. Mow down marginal corn (extremely stressed, dry corners under pivots, etc). Harvest time is also important. Field drying gives Aspergillus flavus more opportunity to infect, especially is drying is slow due to genetics or weather. In the long term, consider on-farm drying options to assist early harvest & rapid drying. Do not leave harvested grain in trucks overnight – this can provide enough warmth and moisture for the fungus to thrive and rapidly produce aflatoxin. A grain moisture level of 15% halts growth and aflatoxin production by Aspergillus flavus. Good sanitation is also important: keep bins and trucks clean, especially after contact with questionable grain.
5. Testing…BLACKLIGHT TEST ILLEGAL IN ARKANSAS, elevator cannot reject corn based on black light. They are required to do a chemical sample. Looking for the maximum 20 ppb that they are testing for in your load of corn is like trying to find 20 painted pennies in 10 million dollars worth of pennies.
Aflatoxin Mitigation Center of Excellence…The Arkansas Corn and Grain Sorghum Board is working with other Southeastern States, as well as, the National Corn Growers to develop a region approach to fighting aflatoxin. The group is creating a system to pool money and University resources to create a cure for the disease that cost producers millions of dollars every year. Through the Center, researchers from different Universities are required to develop joint projects in three main areas: genetics, breeding and new control products.
- 2013 Statement of Allocations to AMCOE
- 2012 Statement of Allocations to AMCOE
2012 Research Project Results – Coming soon!!!
· Biological Control of Aflatoxin Contamination of Corn
· Transgenic Control of Aflatoxin Contamination in Corn through Induces Gene Silencing
· A Transgenic Approach to Improve Resistance to Aspergillus flavus and Reduce Aflatoxin Accumulation In Corn
· Breeding and Testing for Aflatoxin Resistance”
· Identification of Gene-Based Markers for Resistance to Aflatoxin Accumulation in Corn by Examination of the Plant/Pathogen/Environment Interaction
Other Control Methods
· Using Southern States Bentonites to Remove Aflatoxins during Biofuels Production and Optimizing Bentonite Incorporation Methods into Animal Feed Contaminated with Aflatoxins
· Management of Aflatoxin Contamination Through Best Management Practices and Maximizing the Efficacy of Biocontrol