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The survey is conducted in late August
and early September of each year to determine the levels of various
diseases as the soybean crop heads toward harvest. Primary funding
is provided by the Illinois Soybean Checkoff Board.
"This year we are running into large
numbers of fields in the northern and central parts of the state
with severe outbreaks of charcoal rot," said Glen Hartman, USDA
plant pathologist at the U of I. "Jason Bond and his team from SIU
are finding the same results in their part of survey, which covers
the southern half of the state. Basically, anywhere in the state you
stop and look for it, you will find it."
Charcoal rot is caused by a fungus that
can be found in the soil of virtually every field in the state.
Symptoms of the disease will normally show up only during periods of
hot, dry weather.
"Every time we have any drought
conditions at all, we can get charcoal rot," Hartman said. "What
happened this year is that we had a long dry period with high
temperatures in August. Although the early part of the year had
normal weather, this dry spell was enough for the fungus to take
hold and cause the problems we are seeing right now."
He notes that charcoal rot causes the
soybean plants to turn brown and mature early but does not often
kill them outright before podding takes place, especially when the
disease occurs late in the growing season as it did this year.
"Under the current conditions, yield
losses could run from very little up to 30 percent," Hartman said.
"The problem will most often vary greatly within the different parts
of a field. At the same time, I received a call from a grower who
had a field where 95 percent of the plants were infected. In many
cases, the grower does not even know what is causing the problem in
his field."
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Hartman points out that there are
currently no practical options for managing this disease.
"We do not have any resistant varieties
available to recommend to growers," he said. "Rotation probably will
not work, because charcoal rot can infect corn and other common
crops. The only way to control this problem is to irrigate or not
plant soybeans in a field for 10 or 15 years, which is really not
practical at all."
Hartman advocates a two-pronged
research approach for dealing with the problem in the long term.
"We need to look at both biotech and
traditional approaches to finding genetic resistance," he said. "Our
screening for resistance so far has looked at only a small portion
of the 16,000 soybean accessions in the USDA Soybean Germplasm
Collection, housed at the U of I. We may also have to extend the
search to the wild progenitor of the modern soybean and the
perennial relatives of the soybean."
He notes that one problem has been a
lack of consistent support for those research efforts, because the
disease is so weather-related and occurs only in years when there
are drought conditions.
"If we had a
two- or three-year period of dry weather, charcoal rot would
suddenly become the most important disease threat to our soybean
crop," Hartman said. "To be proactive, we should maintain a vigorous
screening program even during those years when it is not a problem.
Eventually we could have resistant soybean varieties available for
growers to plant as insurance against this potentially troublesome
disease."
[University
of Illinois news release]
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