Owensboro, Kentucky
March 5, 2008
By Laura Skillman
Three years after soybean rust
first arrived in the United States, it has yet to become the
disease problem many had feared. But a
University of Kentucky plant
pathologist says it is acting as expected.
“We’ve not been crying wolf,” said Don Hershman, plant
pathologist with the UK College of Agriculture. “It takes awhile
for the disease to build up, and eventually conditions will come
together. I doubt if it’s going to happen every year. Will it be
a one-in-five-year thing or a one-in-10-year thing? There’s
really no way to predict that. You just have to be tuned in and
be ready to act when needed.”
Rust can cause extensive crop damage but can be successfully
treated with timely fungicide applications. Timely applications
depend on finding the disease and monitoring its progression
into the soybean growing areas from the southern United States,
where it overwinters on kudzu. Hershman noted there are more
than 12 million acres of kudzu in this country, primarily in the
South.
“We are noticing that rust seems to be moving north earlier and
earlier every year,” he said. “Part of that is because
pathologists have learned more about how to scout for it.”
A sentinel network of soybean and kudzu plots from Mexico to
Canada are intensively checked from late winter until the end of
the growing season. Pathologists have been successful in
identifying the disease and giving early warning through this
system. Most of the finds are on leaves taken from the field to
a laboratory for incubation and microscopic evaluation.
“We are having more rust finds with each passing year,” Hershman
said. “In 2005, we had 40 finds and 239 in 2007. Part of that is
because kudzu is becoming more uniformly infected. We are also
finding that long distance spore movement is very common, and
that’s the scary part.”
The spores can be lifted and sent for miles during weather
events, but these spores also have to survive the trip and then
find receptive conditions in order to multiply. Large spore
movement does not require a major weather event, such as a
tropical storm or hurricane, but can move northerly on normal
weather patterns. So far spores have found their way into
soybean growing areas and infected plants too late in the season
to impact the crop. But Hershman said as the disease develops
and overwinters in the larger areas of the South, more spores
will be available to move earlier in the growing season.
Pathologists have found that producers have more time to spray
than initially thought once the disease has been discovered.
They have also been able to predict locations where the disease
may pop up using three models that consider spore locations,
spore movement and weather conditions. These models were used to
successfully predict a soybean rust infection in Iowa in 2007.
“It’s always about two and a half to three weeks from the time
it is predicted until it shows up,” Hershman said.
This helps prepare farmers for the potential arrival of the
disease and allows them time to spray fungicides to control its
spread. Timely findings of the disease and the use of prediction
models can help to ameliorate the disease’s impact. Such tools
give farmers information to determine when and if they need to
use fungicides to protect their crop.
“The best defense is a good offense,” he said. “We’ve had three
years now, and we’ve seen three different patterns. The first
year it went up the east coast. The second year it went up the
east coast and through Kentucky, and this year it bypassed
Kentucky and went up through Nebraska. The key for a producer is
to watch the seasonal weather trends and monitor rust
detections, especially in the Deep South, from May through July.
Obviously, the earlier anything begins to happen the worse off
we are going to be – the later, the better.”
Farmers can monitor the rust information at
http://www.sbrusa.net or the
Kentucky Soybean Promotion Board sponsored hotline 888-321-6771.
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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