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Soybean Cyst Nematodes Impacting Kentucky Fields
By
Laura Skillman
PRINCETON, Ky., (Oct. 11, 2006) – Many Kentucky producers are
seeing losses in their soybean fields as a result of a pest they
thought they had under control.
Soybean cyst nematode, SCN, a microscopic roundworm that feeds
on soybean roots and robs the plants of nutrients, is again
being found in large numbers in many fields where varieties
thought to be resistant to the pest were planted. This
phenomenon is happening in a number of other soybean-producing
states as well.
Data collected thus far in Kentucky fields shows a troubling
trend and indicates that many farmers who think they are
successfully managing SCN are, in fact, not, said Don Hershman,
plant pathologist with the University of Kentucky College of
Agriculture.
“I was afraid this was the case, and now we have some data to
back this up,” he said. “Similar data have been collected from
Missouri, Illinois and Indiana. Populations are apparently
shifting due to the overuse of resistant varieties which have
the same source of SCN resistance in their background.”
Simply looking at a stand of soybeans will not indicate there is
a problem with nematodes. Serious yield loss caused by the pest
rarely is associated with obvious disease symptoms in Kentucky.
This results in yield loss often being blamed on other causes,
especially if farmers are using resistant varieties. Producers
may never notice consistent, moderate damage since they may
obtain adequate yields.
“I’ve been working on cyst nematode my entire career, and
because this disease doesn’t usually cause symptoms you’ve got
to wait for a teachable moment,” Hershman said. “In this case,
the teachable moment is that these other states are finding out
that all is not well. My particular interest is that Kentucky
farmers require and should have their own information. So we are
doing the testing to confirm that we’ve got the same thing that
they’ve got going on in Missouri, Illinois and other states in
our region.”
The Kentucky Soybean Promotion Board is funding a free SCN
sampling program for 2006-2007. As part of this program, 45 soil
samples were collected from seven counties this spring.
Twenty-one samples had SCN populations above the damage
threshold, Hershman said.
“This is noteworthy because most of these fields are in a
corn/soybean rotation and were in corn during 2005,” he said.
“We have data that shows how corn rotation can lower SCN in a
field.”
Eleven populations from Ballard, Carlisle, Lyon and Hopkins
counties were sent to the University of Missouri Nematode Lab
for HG testing (formerly called race tests). There were three
different races found but none were Race 3, which historically
has been the predominant race in Kentucky. All 11 SCN
populations were successfully able to reproduce on the primary
source of SCN resistance used in Kentucky and the Midwest,
Hershman said.
Hershman, with the help of county Extension agents, will be
sampling fields again this fall. The samples will come from
fields where soybeans were grown in 2005 and where corn was
grown in 2006.
“We are generating data to prove there is a problem,” he said.
“Farmers have a false sense of security in that they look at the
seed tag; it says resistant to SCN and they move on because
they’ve got a ton of other things to worry about, but that’s not
good enough.”
In Kentucky, most available varieties contain resistance races 3
and 14, said Chad Lee, UK Extension grain crops specialist.
However, there are very few varieties available in Kentucky with
resistance to the races found in the latest round of testing.
Resistance information usually is printed on the tag attached to
each seed bag.
Within a few years, Kentucky farmers likely will have more
resistance options available to them, but for now the best
option to combat the problem is crop rotation, Lee said.
Information garnered through UK and other universities will help
seed companies in their variety development.
Hershman said growing another crop besides soybeans in a field
may need to be done for more than a single year to significantly
lower SCN levels in problem fields.
Farmers who want to have their field checked, can contact their
county Extension office. |
Contact: Don Hershman, 270-365-7541, ext. 215
Chad Lee, 859-257-3203 |
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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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