Michigan State University Extension
Michigan Soybean Information - FACT2000
11/16/00
Roundup and Cobra Applications in Soybeans Impact on Canopy Development and Incidence of White Mold
List of files and visuals associated with this text.
Soybean Facts January 2000
PDF version of this document available at: (Fil. 1)
K.A. Nelson and K.A. Renner, Department of Crop and Soil
Sciences, Michigan State University, R. Hammerschmidt,
Department of Botany and Plant Pathology, Michigan State
University Research Funded by the Michigan Soybean
Promotion Committee
White mold is a major pest problem in Michigan and other
midwestern states. Producers options for white mold control
are limited. This fact sheet is for producers who are
interested in the effects of herbicides on white mold
incidence in Roundup Ready and non-resistant soybean.
With the introduction of Roundup Ready soybean,
several producers have shifted production to narrow-rows
(< 30 inches). White mold is a common problem in narrow-row
soybean production systems because white mold infection is
dependent on cool, moist conditions during flowering. Early
canopy closure in narrow-row soybean results in a
microclimate that encourages the infection and growth of
white mold. Cultivar selection, crop rotation, tillage, row
spacing, population, and clean seed should be monitored to
help manage white mold. For more information on these
topics see Soybean Facts, White Mold in Soybeans. For every
10% incidence of white mold in the field, there may be a 2
to 5 bu/acre yield loss. However, at low levels of disease,
soybean yield may not be reduced due to yield compensation
of nearby soybean plants. The effect of white mold on yield
is very dependent on cultivar selection. The Michigan State
University Soybean Performance Report Provides information
about the susceptibility of public
and private cultivars to white mold.
Several questions have been asked regarding the
susceptibility of Roundup Ready soybean to white mold and
if Roundup increases the incidence of white mold in Roundup
Ready soybean. In addition, questions about the effects of
Cobra on white mold have been frequently asked.
This fact sheet provides information on: 1) the
susceptibility of Roundup Ready soybean compared to near
isogenic non-resistant soybean, 2) the effect of Roundup
Ultra on the incidence of white mold in Roundup Ready
soybean, and 3) the effects of Pinnacle plus nonionic
surfactant plus 28% N and Cobra plus nonionic surfactant
plus 28% N on soybean canopy development and the incidence
of white mold in Roundup Ready and non-resistant soybean.
Were Roundup Ready soybean more susceptible to white
mold than non-resistant soybean? Near isolines of Roundup
Ready (NKS14-M7, NKS20-B9, GL2600, and P93B01) and
non-resistant soybean (NKS12-49, NKS19-90, GL2415, and
P9281) had similar incidence of white mold, Figure 1
(Vis. 1) and yield, Figure 2
(Vis. 2) in 1998 and 1999.
Figure 1. White mold disease severity index (DSI) for
Roundup Ready (S14-M7, S20-B9, GL2600, and P93B01) and
non-resistant soybean (S12-49, S19-90, GL2415, and P9281).
(Vis. 1)
Figure 2. Soybean yield for Roundup Ready (S14-M7, S20-B9,
GL2600, and P93B01) and non-resistant soybean (S12-49,
S19-90, GL2415, and P9281).
(Vis. 2)
Did Roundup Ultra increase the incidence of white mold
in Roundup Ready soybean compared to no herbicide
application? Roundup Ultra did not affect soybean growth
characteristics, disease severity, Figure 3A(Vis. 3), or
soybean yield compared to no herbicide application in 1998
and 1999, Figure 3B(Vis. 3).
Figure 3. Incidence of white mold (DSI) and yield following
no herbicide and Roundup Ultra in Roundup Ready soybean.
(Vis. 3)
Did other postemergence herbicides reduce soybean leaf
area and the incidence of white mold in Roundup Ready and
non-resistant soybean? Pinnacle and Cobra injured soybean
3 to 17% 7 days after treatment and reduced canopy
development 3 to 28 days after treatment compared to
untreated soybean, Figure 4(Vis. 4). Cobra increased
phytoalexin production 2 to 26 days after treatment and
reduced the incidence of white mold compared to no
herbicide application, Figure 5(Vis. 5). A phytoalexin is
an antimicrobial compound produced by a plant in response
to a pathogen or abiotic factor. Cobra and Pinnacle did not
affect soybean yield compared to no herbicide treatment in
1998 and 1999, Figure 6(Vis. 6).
Figure 4. Soybean canopy development for untreated,
Pinnacle and Cobra herbicide treatments. (Vis. 4)
Figure 5. White mold disease severity for untreated,
Pinnacle, and Cobra herbicide treatments. (Vis. 5)
Figure 6. Soybean yield for untreated, Pinnacle, and
Cobra herbicide treatments in the presence of white mold.
(Vis. 6)
In summary, soybean tolerance to white mold was not
related to Roundup resistance. Roundup Ultra did not affect
the incidence of white mold in Roundup Ready soybean. Cobra
reduced the incidence of white mold compared to Roundup
Ultra, Pinnacle, or no herbicide application. A
postemergence application of Cobra affected several soybean
growth characteristics and increased phytoalexin
production. However, an increase in soybean yield with
Cobra did not occur in this research.
This information is for educational purposes only. References
to commercial products or trade names does not imply
endorsement by MSU Extension or bias against those not
mentioned. This information becomes public property upon
publication and may be printed verbatim with credit to MSU
Extension. Reprinting cannot be used to endorse or advertise
a commercial product or company.
This file was generated from data base S1 on 11/16/00.
Data base S1 was last revised on 11/16/00.
For more information about this data base or its contents please contact
reinholt@michigansoybean.org . Please read our
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