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But, according to Dean Malvick, plant
pathologist from University of Illinois Extension, several plans
and operations are already in place to provide information on when
and how growers should respond to this threat.
"Fortunately we have had several
years to gather information on Asian soybean rust in South America
and Africa," Malvick said. "Even so, there are still many
questions about what to expect and how to plan for managing
soybean rust in Illinois. In fact, the speculation may exceed the
solid information that is currently available."
He points out that many of the
answers, such as how the spores will be dispersed to the state and
how favorable the conditions are for the disease, may not come
until soybean rust disease actually arrives in Illinois and nearby
states.
"We know the states and counties
where soybean rust was found in November and December 2004,"
Malvick said. "We also know that soybean rust survived over the
winter in Florida and has been confirmed in three counties in
Florida and in one area of Georgia."
Additional information on where
scouting has been conducted and where soybean rust is confirmed
can be found on the USDA website at
www.sbrusa.net.
"Some assumptions suggest that the
severity and incidence of soybean rust in Illinois will be linked
to what happens in states such as Arkansas, Louisiana and
Tennessee," Malvick said. "The disease must reach at least a
moderate level in those or other southern areas to act as a
sufficient source of spores to be blown into and initiate disease
in more northern soybean production areas, including Illinois."
As a result, he points to the
reports from the South as the most likely indicator of subsequent
risks in the northern states. In addition, extensive efforts have
been made this winter to develop a forecasting system for
dispersal of soybean rust from source areas to other areas that
may be vulnerable.
"The forecasts are updated daily
and are an interesting and potentially very valuable tool to
assist in preparing and predicting where and when soybean rust may
occur," he said. These experimental forecasts are readily
available on the Internet at
http://www.ces.ncsu.edu/depts/pp/
soybeanrust/forecasts/s050411.php.
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Malvick points to the environment as
another factor that must be suitable to initiate and propagate a
rust epidemic in Illinois.
"Long dew periods with free water on
leaf surfaces and moderate temperatures between 66 and 82 degrees
Fahrenheit favor soybean rust," he said. "In Brazil, soybean rust
epidemics in different regions have been associated with the amount
and frequency of rainfall. For example, wet areas in a single
growing season had high disease severity, while dry areas in the
country had low regional disease severity."
In the parts of Brazil where soybean
rust has frequently been severe, the average amount of rainfall in
the main part of the growing season is about 24 inches. The average
in Urbana from June to August is about 11 inches.
"Soybean rust could be similar to
southern rust of corn, which is an infrequent problem," Malvick
said. "In Illinois, that problem mostly occurs only late in the
growing season."
Risk analysis based primarily on
average historical climatic conditions suggests that the most
frequent problems with soybean rust in the U.S. soybean production
areas will occur in the southern and eastern regions.
"Sentinel plots for soybean rust
monitoring, which will be distributed across Illinois and throughout
the soybean producing states, will provide information on where and
when soybean rust is occurring," he said. "Soybean rust can be a
very serious disease and should be monitored and prepared for
appropriately."
He points out that a key time to
begin scouting for soybean rust and to consider fungicide
applications appears to be in the late vegetative and early
reproductive stages. This would be especially true after the disease
forecasts and scouting reports from sentinel plots and states to the
south of Illinois indicate that movement of soybean rust into
Illinois is likely.
"Initial scouting should focus in
the lower parts of plants, where the disease usually occurs first,"
Malvick said. "The early lesions and pustules can be seen most
clearly with a hand lens at 20X magnification. We have much to learn
about this disease in the United States, but soybean rust can be
managed at a cost."
[University of Illinois news
release] |
