Biological
      control aids in
reducing aflatoxin

   A biological control product available to farmers in 2005 enables farmers to reduce the naturally occurring Aspergillus flavus on the farm. By treating peanut fields with barley coated with spores of a non toxigentic A. flavus farmers are able to reduce aflatoxin by 85 percent, so says experts with the National Peanut Research Laboratory.
   The relatively new product, Afla-Guard, received EPA approval in May 2004 after seventeen years of development and testing. Circle One Global, Inc. of Cuthbert, Ga., is the sole licensee of the product.
   According to Joe Dorner, microbiologist with the USDA-Agricultural Research Service National Peanut Research Laboratory (NPRL), Afla-Guard was applied using microband applicators in 2004 that dropped Afla-Guard in a band over the row. The Afla-Guard fell to the soil surface around the base of the plants.
   Recently, EPA approved aerial application of Afla-Guard as well as broadcasting the material with something similar to fertilizer spreading equipment, Dorner adds.
   Regardless of method, the rate is 20 lbs/acre, Dorner says.
   "It is best applied about the middle of the growing season when peanuts are almost lapped, or you have nearly complete closure of the foliage canopy," he says. "This provides the optimum environment for the competitive fungus to grow and sporulate on the barley carrier."
   Aflatoxin is a naturally-occuring mycotoxin produced by two types of mold: A. flavus and Aspergillus parasiticus. A.flavus is common and widespread in nature. It is most often found when certain nuts and grains, particularly peanuts and corn, are grown under stressful conditions such as drought.
   Dorner and colleagues at NPRL in Dawson, Ga., made the biological treatment from spores of a nontoxigenic strain of A. flavus that is applied to barley kernels. The kernels are then applied to the soil beneath the plant canopy, where the fungus colonizes the barley and establishes itself to compete against toxigenic strains of A.flavus that are naturally present. Other strains of A. flavus, as well as A. parasiticus, are the primary producers of aflatoxin.

   These non-toxin producing strains significantly reduce aflatoxin contamination of the peanuts at harvest and equally importantly, during storage.
   Aflatoxin costs peanut growers in the Southeast U.S. in excess of $27 million in an average year and the cost to the peanut shelling and manufacturers has neared $100 million in yeas where drought has been a significant factor, reports Circle One Global.
   Although the timely application of Afla-Guard during preharvest of the crop prevents contamination, an equal or greater benefit is experienced during post-harvest storage. According to data from Circle One Global, reductions in aflatoxin of 97 percent were also seen in a two-year storage study of peanuts that had been treated with Afla-Guard in the field and then stored under conditions conducive to fungal growth.
   "Not only does this save millions of dollars in losses incurred by the shelling industry but it also eliminates virtually any potential traces of aflatoxin at the process stage of manufacturing finished peanut products," says Alvin Jones, secretary/treasurer of Circle One Global.
   Field treatment of peanuts with Afla-Guard has cut aflatoxin levels in peanuts from 75 to 90 percent in a number of replicated studies during the past several years but that may not be all of the advantages. According to Dan Gay, president of Circle One Global, some growers reported a decrease in white mold and limb rot by using Afla-Guard. There are several researchers looking into this possible advantage during the 2005 growing season.
   Growers interested in trying Afla-Guard on their 2005 peanut crop should contact Circle One Global directly at 229-732-3101.

By Joy Carter

Biological Control
Technology has been developed for biological control of aflatoxin contamination.
A competitive, nontoxigenic strain of Aspergillus flavus is applied to soil where it
displaces the strains that produce aflatoxin.

Untreated

Number of samples

178

Average aflatoxin (ppb)

78.9 ppb

% Loads >100 ppb

2.2

Average aflatoxin reduced by 85.2%.
Percent of loads with >100 ppb reduced by 86.5%.

  Aflatoxin and resulting Segregation III peanuts can
become a serious problem in the Southeast, particularly during
years of extreme drought during the last 30 to 40 days of the
growing season. Aflatoxin has been shown to be higher in
damaged kernels, loose shelled kernals (LSK's), and immature
peanuts. Production practices which reduce aflatoxin risk
include:
Well-irrigated peanuts - When late season drought occurs
and kernel moisture drops below 35 percent, peanuts are high-
ly susceptible to fungal infection and aflatoxin is likely to
develop.
Proper pest control - This reduces the risk of aflatoxin
problems. Healthy plants maintained by good disease manage-
ment will mature more uniformly and be less likely to have a
high percentage of immature or over-mature peanuts which
are more susceptible to fungal infection. Soil insect injury,
particularly from lesser cornstalk borers, also provides an
opportunity for aflatoxin development. The drought conditions
that are favorable for aflatoxin development are also favorable
for soil insects.
Correct combine operation - Operate combines to mini-
mize machanical damage. Sound mature peanuts usually are
free of aflatoxin while loose shelled kernels (LSK's) are much
more likely to be contaminated with aflatoxin as well as high
moisture immature peanuts.

Cleaning of combines and trailers - Previous crop
residue in combines and trailers can be a source of contamination and should be cleaned out before harvest.
Separation of irrigated and non-irrigated peanuts -
Avoid mixing peanuts harvested in irrigated fields with
peanuts grown without irrigation.
A new material, Afla-Guard, has been released to reduce
in-field aflatoxin potential.
     Causes of sound splits and LSK's:
- Combining when field moisture content is below 18 percent or above 24 percent.
- Drying below 10 percent final moisture content.
- Drying more rapidly than 2 percent per hour moisture
removal.
- Relative humidities below 50 while curing.
- Rough handling after any of the above.
- Rain on windrowed peanuts.
   If peanuts are combined with moisture content above 24
percent, mechanical damage usually becomes apparent. This is because dents are caused in peanuts where mold can form before drying is completed, as well as showing up as physical peanut hull damage after curing.

BY JOHN BALDWIN
EXTENSION PEANUT AGRONOMIST
UNIVERSITY OF GEORGIA