But, according to a recent on-farm
study at the University of Illinois conducted with funding from the
Illinois Soybean Checkoff Board, nearly all growers in the state
would probably benefit from planting SCN-resistant varieties.
"There has been a lot of concern by
growers because of the history of resistant varieties not producing
well on ground that does not have SCN," said Greg Noel, USDA
nematologist in the Department of Crop Sciences at the U of I. "The
reality is that there are probably very few fields in Illinois that
do not have at least some cyst nematodes in them."
Noel has conducted two years of on-farm
trials at seven locations in central Illinois and western Indiana on
fields ranging from no infestation to moderate levels of infestation
by SCN. Each field was planted with four varieties: a susceptible
variety, a variety with low levels of resistance from the Fayette
line, a variety with higher levels from the same line, and a variety
with the Peking line of resistance.
"These trials were carried out on
farmers' fields, and all operations were done with their own
equipment," Noel said. "Each variety was planted the full length of
the field, randomized and replicated three times. Yield was
determined with a weigh wagon, and moisture was corrected to 13
Although yield drag up to 10 percent
from resistant varieties was confirmed in fields with no nematodes,
the study pointed to a major difficulty in making the determination,
without extensive testing, that nematodes are not present.
The study further confirmed that
planting resistant varieties most often paid off in fields with even
low levels of SCN infestation.
"At some locations where we found no
nematodes prior to planting, we sampled that same site at harvest
and found fairly large numbers of nematodes," he said. "That means
there is a lot of error in undertaking the common methods used in
sampling for nematodes."
He notes that growers can have yield
losses as high as 10 percent to 15 percent from nematodes in fields
where there are no outward signs of damage. In most cases, those
fields appear to the eye to have completely filled-in rows and to be
growing perfectly well.
"Part of the dilemma that growers face
is the fact that there is no accurate way of telling what numbers of
nematodes they have in a particular field," Noel said. "In our
experiments, we took four samples of 20 cores in each round, for a
total of 48 samples and 960 soil cores in each field.
He points out that current
recommendations for sampling just do not adequately represent what's
in the field.
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"It's not anyone's fault," Noel said.
"In order to rectify the situation, a grower would have to spend a
lot of money and take a lot of samples, which is just not worthwhile
According to Noel, growers who have any
history of SCN problems should always plant SCN-resistant varieties.
Even growers with no clear signs of a problem should also strongly
consider planting a resistant variety as a form of no-cost
"Although yield drag does occur in
fields with zero or low nematode populations, the problem is trying
to determine whether or not you have a low population," he said.
"The troubling thing is that you can have a fairly significant yield
loss from SCN and not even know you have it. In those cases, a
resistant variety would certainly pay off in higher yields."
Despite the problems with sampling,
Noel suggests that growers can take some simple steps to improve
their chances for selecting the proper variety for their fields.
"One way is to monitor the yields as
you move through a field," he said. "By checking the yield monitor,
you can look for drop-offs and then flag the area. Then you can come
back to those areas and take samples for SCN during the fall."
Noel adds that valuable information is
also available from the Varietal Information Program for Soybeans
maintained at the U of I. This VIPS database provides unbiased
information on soybean varieties from a wide range of companies,
including evaluations of resistance against various nematode
populations. The varieties entered in the trials were tested at 13
different sites around the state of Illinois.
In the 2003 soybean trials, there were
134 conventional varieties and 661 Roundup-resistant varieties from
70 companies. Besides those entered by participating companies, the
total number of soybean varieties included 244 that were nominated
by Illinois farmers and entered directly by the Illinois Soybean
"Growers can easily use this invaluable
resource to help make an informed decision on what specific
varieties to plant," Noel said. "I would suggest finding the test
location near where a grower lives and identifying a resistant
variety that has the highest level of resistance and the highest
information from the VIPS database is available on the Internet at
of Illinois news release]