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Dry Conditions Limit Soybean Rust, Encourage
Charcoal Rot
By
Laura Skillman
PRINCETON, Ky., (Sept. 5, 2007) – Soybean rust spores likely
blew into some areas of north and north central Kentucky from
remnants of Tropical Storm Erin but in extremely low levels, and
most of the state was not touched. As a result, while there is
much rust activity in many nearby states, there’s little cause
for concern in Kentucky, says a University of Kentucky College
of Agriculture plant pathologist.
In most areas of the state that are still very hot and dry,
drought and or charcoal rot are the greatest production risks to
soybeans, said Don Hershman, UK plant pathologist. The fungus
that causes charcoal rot is present in all agricultural soils in
Kentucky where soybeans are commonly produced and favors hot,
dry conditions.
“Charcoal rot and drought will be the biggest yield limiting
factors in this year’s soybean crop,” Hershman said.
Most plants are infected with the fungus, but it remains largely
dormant unless high temperatures and low soil moisture coincide
with plants in the reproductive stages, he said. Charcoal rot is
also exacerbated in weakened plants which can result from poor
soil fertility and excessive seeding rates. The disease then
increases as the stressed soybean plants approach maturity.
Premature death of affected plants is a common outcome.
Yields can be severely compromised by charcoal rot. However,
because the disease is most common during drought conditions,
most producers attribute low yields in dry years to lack of
sufficient soil moisture and do not usually realize that
charcoal rot has also taken a toll. Under moderate drought
conditions, affected plants usually occur in patches associated
with compacted soils or on hills. In a severe drought, large
percentages of fields may show evidence of disease.
Hershman said he expects soybean rust likely will be found in
Kentucky sometime in September, a month earlier than last year
but too late for any damage to occur to full season beans. Only
double-cropped plantings could be at risk.
“People are hearing a lot about it because of the finds in other
states, but the main thing is for Kentucky farmers not to get
too concerned,” he said. “If it did drop spores in Kentucky, and
I believe it did, we are still several weeks away from it
developing enough for us to even find it, much less needing to
spray for it.”
This is because the initial level of spores deposited is
predicted to have been very low and some likely died due to UV
radiation when the sun reemerged in areas that received
rainfall.
“In my opinion, the absolute earliest we may need to treat
soybeans in potentially impacted parts of the state would be
late September,” Hershman said. “By that time, most full-season
crops will be far enough along that spraying will not be
necessary. Double crop beans continue to be at greatest risk for
possible damage by SBR where rains have occurred.”
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Contact: Will Snell, 859-257-7288
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The UK College
of Agriculture, through its land-grant mission, reaches across
the commonwealth with teaching, research and extension
to enhance the lives of Kentuckians. |
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Kentucky Cooperative Extension Service |
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