| July
13, 2006: The ancient Romans prayed to Rosbigus,
the god of rust who could protect their crops from (to them)
mysterious diseases in harvested wheat and in stored bread
during winter months. Ceremonies were given to allay this
deity so the cereal crops—needed for the daily sustenance
of Rome—were productive and safe to eat.
Today, the huge multi-billion dollar United States soybean
crop is threatened by Asiatic Soybean Rust (ASR), a fungal
disease caused by Phakopsora pachirhizi. This pathogen
can eliminate up to 90 percent of soybean yield under severe
epidemic environments. While varieties vary in their tolerance,
no commercial strain has resistance to this rust.
The ASR fungus originally wrought havoc in Asia and Africa,
hitting more recently Brazil and the United States. Hurricane
Ivan is attributed with bringing ASR spores to Florida from
South America or Africa in the fall of 2004. By the end of
2004, soybean rust was identified in about eight counties,
mostly in the panhandle of northwestern Florida. By the fall
of 2005, the same rust was identified in about 10 states and
in 138 counties.
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As important as soybeans are to the US ag economy in terms
of quantity—hence, the threat of a catastrophic disease
exposure—they are prominent in organic production due
to their distinctive quality. Because of consumer concerns
about Roundup Ready genetically modified soybeans in food
products, there has been increasing demand for organic soybeans
over the last decade. Because there has been no confirmed
defense against ASR that was permissible under the rules of
the USDA’s National Organic Program, the viability of
organic beans seemed to be in danger, especially in the southern
states.
Better news in 2006
But wait. If you are an organic soybean farmer it’s
way too early to give up on the crop, given differences developing
this season. By early July, the number of counties with soybean
rust was only up to 24, all of them in the Deep South relatively
close to the Gulf of Mexico. Soybean rust, like soybeans,
will overwinter only in southern Florida and Texas. The overwintering
host has been shown to be kudzu (Pueraria spp.),
the notorious runaway forage vine that cascades over trees
in the Southern summer but only survives unfrozen on live
leaves at the most southerly points of the continental US.
More good news: AgraQuest, a venture capital group developing
biocontrol organisms for disease and pest management, has
registered the first organically approved biocontrol specifically
formulated for rust. In 2005, results both within and outside
the United States shows Ballad biocontrol fungicide significantly
improves both yield and protects against many non-rust diseases
to boot.
Bacillus pumilus (BP) is a patented biocontrol bacteria
in the same genus as Bacillus thuringiensis (BT).
Many organic farmers are well aware of BT for its ability
to control caterpillar pests. These bacteria produce a resistant
endospore, which allows a biological agent to survive commercial
storage and distribution without decreasing insect or disease
control in BT or BP, respectively.
In addition to direct action to kill rust, B. pumilus
works by activating the soybean plant defense system as well
as both blocking leaf-to-rust-spore contact and through the
action of potent amino sugar antifungal antibiotics. This
last action is expressed by inhibiting fungal cross-wall formation,
new cell development, and destroying membranes, which leads
to pathogen cell death. In addition, the soybean rust action
has been demonstrated on septoria brown spot, frogeye leafspot
(Cercospora sojina), soybean powdery mildew (Microsphaera
diffusa) and purple leaf blight and seed stain (Cercospora
kikuchii).
Controls pay for organic beans
But does the application pay? Average yield increases from
two to four applications is 17 percent. This would cost about
$20 to $40 approximately per acre for a seven-bushel bump
on 45 bu/ac beans. Whereas for conventional beans this might
have a value of about $40 an acre—being near a wash—in
the case of $10 organic beans, this would be a value of at
least $70 dollars per acre on the same yield potential. Wholesale
prices reported from seven terminal markets as July 11 ranged
from $9.50 to $14.50 per bushel for certified organic soybeans,
according to The New Farm Organic
Price Index.
Ballad fungicide is used at two quarts per acre and applied
at 14-day intervals starting at or slightly before or after
start of flowering at the R1 stage. For growth stage details,
visit:
www.ext.nodak.edu/extpubs/plantsci/rowcrops/a1174/
a1174w.htm.
Trials in South Africa concluding in March 2005 showed Ballad
applications of two quarts per acre gave 95 percent control
of soybean rust—not statistically more significant than
the synthetic chemical control azoxystrobin. There were also
two trials in 2005 in Argentina. In the first trial, yield
was increased five bushels per acre with a 10-percent decrease
in soybean rust. In the second, one application at the R5
stage (just before full green-bean stage) reduced rust by
96 percent and bumped yield by 17 bushels—two bushels
per acre more than the mixture of synthetic fungicides tested.
We are collaborating with Iowa State University, University
of Florida and Michigan State University to examine ASR controls
for organic farmers. Our Florida collaborators tested Ballad
with three applications at R1 that showed rust decreased about
two-thirds.
Dr. Boyd Padgett of Louisiana State University showed Ballad
bumped the yield by seven bushels per acre—almost 50
percent over non-treated by controlling Cercospora Leafspot
in the absence of rust in 2005.
We plan to look at Ballad closely in Pennsylvania this year
and, although we do not expect soybean rust, we will see how
it (in addition to lime sulfur and soybean oil treatments)
does on other diseases and get our feet wet on the product.
Soybean rust was reported as far north as North Carolina and
Missouri last year, so you may want to be particularly careful
this year scouting your fields, particularly below the Mason-Dixon
line.
I don’t know if praying to the rust god will work for
you, but being prepared with information on ASR and its management
will definitely help put you ahead in the rust game. 
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