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Continued from Page 6<br />
persisted well until the next application<br />
in the following year and displaced the<br />
toxigenic A. flavus strains at a rate of<br />
90 to 95 percent displacement. These<br />
results, the fact that this strain was<br />
native to California orchards, and it<br />
was the most common atoxigenic strain<br />
and the toxicological data developed<br />
by the USDA in Arizona were sufficient<br />
to submit to the Environmental<br />
Protection Agency (EPA) to request<br />
an experimental use permit (EUP) to<br />
test the strain commercially on a larger<br />
acreage without the need to follow<br />
crop destruct requirements as needed<br />
with application of experimental<br />
compounds. The EUP was approved<br />
in 2008 and 3,000 acres of pistachios<br />
were treated with the commercial<br />
product of Aspergillus flavus AF36<br />
strain produced in the Cotton Council<br />
of Arizona facility in Phoenix, Arizona.<br />
Also, 3,000 acres of pistachio close to<br />
the AF36-treated orchards were used<br />
as untreated controls. All this acreage<br />
for the EUP was provided by the former<br />
Paramount Farming Company (now<br />
Wonderful Orchards Company). At<br />
harvest the treated and the untreated<br />
fields were sampled separately and the<br />
samples, specifically called “library<br />
samples”, were analyzed for aflatoxins.<br />
For four years we showed a significant<br />
reduction of aflatoxins (Figure 2A, see<br />
Page 6). The average of this reduction<br />
for the four years of the EUP was close<br />
to 40 percent. When library samples of<br />
reshakes were analyzed for aflatoxins,<br />
this reduction in one year reached to<br />
85 percent (Figure 2B, see page 6).<br />
These commercial efficacy data were<br />
sufficient to obtain registration of<br />
AF36 for use in pistachio in the states<br />
of California, Arizona, Texas, and<br />
New Mexico. After the registration<br />
of AF36 on pistachio, the Almond<br />
Board of California and the California<br />
Fig Institute (the latter has funded<br />
research during the early stages of our<br />
aflatoxin research) became interested<br />
in completing any additional research<br />
so that the AF36’s registration is<br />
expanded to include almonds and figs.<br />
It took five years of additional research<br />
(funded by the Production Research<br />
and Food Safety and Quality<br />
Committees of the Almond<br />
Board of California) to<br />
provide the USEPA and the<br />
California Department of<br />
Pesticide Regulations the<br />
additional data for the registration<br />
of AF36 for use on<br />
almond and figs. Meanwhile<br />
because the manufacturer<br />
of the commercial product<br />
changed the initial wheat<br />
carrier of the AF36 strain<br />
to sorghum (Figure 3) the<br />
product was registered as<br />
AF36 Prevail® in January 2017<br />
and included all, pistachio,<br />
almond, and fig. Although the<br />
pistachio industry adapted the<br />
use of AF36 widely and from<br />
75,000 acres treated in 2012 reached to<br />
up to 200,000 acres in 2018, the almond<br />
industry was a little hesitant in widely<br />
adopting this new technology, despite<br />
the fact that there was good efficacy<br />
in reducing aflatoxin contamination<br />
in pistachio orchards. We expect to<br />
see better efficacy when all pistachio,<br />
almond and fig orchards are treated<br />
on an areawide basis because the<br />
spores of the biocontrol can spread<br />
from field to field easily with even<br />
slight windy conditions and dust.<br />
Description of the Biocontrol<br />
Product<br />
Initially the AF36 product used sterilized<br />
wheat as the carrier. Sterilized<br />
wheat seed was inoculated and incubated<br />
under certain favorable conditions<br />
for the strain to invade and grow<br />
in the entire wheat seed. More recently<br />
and after additional studies in Arizona<br />
it was determined that sorghum, which<br />
has a lower cost was as good carrier as<br />
the wheat (even better under conditions<br />
in cotton and corn fields) and the<br />
manufacturer replaced the wheat with<br />
sorghum and at the same time changed<br />
the method of inoculation. The sorghum<br />
seed now is coated with a mix of<br />
a polymer and spores of AF36 instead<br />
of waiting for the seed to be colonized<br />
by the atoxigenic mold. This was<br />
done in order to satisfy the increased<br />
demand for tons and tons of inoculum<br />
since the rate is 10 lbs per acre. Studies<br />
Figure 3<br />
The sorghum career of the AF36 Prevail® commercial<br />
product.<br />
in California under orchard conditions<br />
indicated that the sporulation on the<br />
sorghum seed is delayed, although by<br />
the end of a week both sorghum and<br />
wheat showed similar sporulation rates.<br />
The time of production of spores and<br />
the rate of sporulation are very critical<br />
for the successful use of this biocontrol<br />
agent. It is a numbers game: we want<br />
to overload the soil with atoxigenic<br />
spores and displace the spores of the<br />
toxigenic molds. That is the way this<br />
biological control approach works in<br />
the field (see challenges at the end of<br />
this article relevant to sporulation).<br />
Proper Way for Ground Application:<br />
For detailed information please<br />
read the label of the product:<br />
Michailides emphasized that as far<br />
as we know up to now there are<br />
four critical application factors that<br />
need to be taken into account for<br />
AF36 Prevail to be successful in the<br />
orchard: a) the timing of application;<br />
b) the rate (amount) per acre; c) the<br />
proper placement on the orchard<br />
floor; and d) the proper irrigation<br />
before and after the application.<br />
Continued on Page 10<br />
8 Progressive Crop Consultant <strong>Nov</strong>ember / <strong>Dec</strong>ember <strong>2019</strong>