Michigan State University Extension
Michigan Soybean Information - FACT9804
11/16/00
Chemical Control of White Mold
Soybean Facts
Michigan State University Extension
This research and fact sheet funded by Michigan
Soybean Promotion Committee Making Your Checkoff Pay Off
Winter 1998
By: Ray Hammerschmidt(1)
Elizabeth Dann(1)
Brian Diers(2),
Michigan State University
(1)Department of Botany and Plant Pathology and
(2)Department of Crop and Son Sciences,
The white mold disease, also known as Sclerotinia
stem rot, is caused by the fungus Sclerotinia
sclerotiorum. The disease can be a very severe prob-
lem in soybean fields during cool, wet summers. The
fungus needs wet conditions to both produce spores
and for the spores to infect the plants. Over the past
few years, a number of chemical control methods have
been experimentally tested to determine if they are
effective in controlling white mold in the field. The
research results presented in this fact sheet are based
on research supported by the Michigan Soybean
Promotion Committee through the soybean checkoff.
Chemical Practices Tested:
1. Resistance inducing compounds
All plants have the genes needed to stop pathogen
infection. However, these genes are not activated until
disease is established in a susceptible plant. We have
field tested a set of compounds that control disease by
increasing the plant's own resistance mechanisms. One of
the compounds tested (BTH, produced by Novartis) is now
registered for use on cereals in Germany. Treatments with
resistance inducing compounds have resulted in a 0-50%
reduction in the plants infected by white mold, and these
reductions in disease have resulted in yield increases of
0-30%. No effect, however, was observed in 1997. The
largest effects of these compounds were found in
locations with high rates of white mold infection and on
varieties that are most susceptible to the disease. Up to
three treatments with the compounds are needed to obtain
significant reductions in disease.
2. Herbicides
Herbicides were evaluated in 1995-1997 for their
effectiveness in reducing severity of white mold. These
studies were initiated because of reports from growers
that some post-emergence herbicides reduced white mold
severity and because there have been reports of herbicide
treatments reducing disease severity in other crops. The
herbicide Cobra(R) was evaluated in all three years using
one application at a rate of 6 oz. plus 1 pint crop
oil/acre. In 1995 and 1996, Cobra(R) applications at V3
resulted in about a 50% reduction in the number of plants
infected with white mold. The reduced infection rates
were, however, associated with only slight yield
increases. White mold severity was reduced in 1997 when
Cobra(R) was applied at several rates at R1. These R1
applications resulted in yield increases where disease
severity was high, but Cobra(R) treatment resulted in
yield suppression under low disease pressure. Other
tested herbicides did not have any effect on white mold
severity when applied at R1 stage of growth. Application
of Cobra@ at V3-4 resulted in reduction of white mold
severity at two research sites in 1995 and one site in
1996. No effect was seen when Cobra(R) was applied at V4
in 1997. No increase in yield was observed where the
disease was reduced.
In summary, application of Cobra(R) at the R1 stage of
growth has the potential of reducing white mold severity
and increasing yield under high disease pressure.
However, we have also observed reduction of white mold
without any yield benefit when Cobra(R) is applied at
V3-V4 growth stages as well as a suppression of yield
when Cobra(R) is applied in the absence of high disease
pressure.
This research and fact sheet funded by Michigan Soybean
Promotion Committee Making Your Checkoff Pay Off
Copies of the Soybean Research Fact Sheet are available
from:
Michigan Soybean Promotion Committee
http://www.michigansoybean.org
MSUE County Office
http://www.msue.msu.edu/msue/ctyentpg/
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endorsement by MSU Extension or bias against those not
mentioned. This information becomes public property upon
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