Ames, Iowa
December 8, 2008
Source:
Iowa State
University's
Integrated Crop Management newsletter
Daren Meuller, Department of Plant Pathology
http://www.extension.iastate.edu/CropNews/2008/1125mueller.htm
While 2008 will be known for its
early season rains, this did not translate into soybean rust
arriving in Iowa. Soybean rust was reported in Alabama, Florida,
Louisiana, Mississippi, Texas and Mexico in January. However,
dry weather during early spring in southern Texas and Gulf Coast
states helped keep soybean rust from building up inoculum and
spreading early in the season.
 Since
January 2008, soybean rust has been reported in 396 counties in
the U.S. and Mexico, which is more than any previous year (Table
1). However, many of these finds were late in the season, more
so than in previous years.
Another bullet dodged
So what happened? Why did soybean rust once again fail to infect
soybeans and cause yield loss in Iowa? Soybean rust overwintered
in the right (or wrong, depending on your perspective) places
and we had plenty of rain. There were hurricanes and other storm
systems coupled with cooler-than-normal temperatures for
portions of the summer that provided ideal conditions for
disease establishment and development. We even had a
late-planted crop and a season that lagged about two to three
weeks behind, extending the vulnerable period for yield loss
into early September.
Despite all of these factors that increased our chances for
getting soybean rust, we didn’t. In most of the places where the
pathogen overwintered, it petered out as spring became summer.
Disease did not spread or completely disappeared in the
overwintering sites in Alabama, Mississippi, Louisiana and
Texas. The infected crops in Mexico were harvested. Bottom line,
the inoculum did not build up in the south like it did in 2007.
So all of the storms that would have been major problems in 2007
were not, as there was little to no inoculum to transport.
 Website
and Fast Track System Overhauled
The Iowa State University Soybean Rust Web site was redesigned
in 2008. The new site highlights weekly messages written
throughout the growing season that provide up-to-date
information on soybean rust. Individuals can sign up to have
these reports e-mailed to them. The website also provides the
basics and management of soybean rust, as well as fast facts
about soybean rust.
In 2004, the Soybean Rust Fast Track System was put in place to
ensure rapid identification of soybean rust through first
detectors. Since then, more than 700 individuals were trained as
first detectors. One of the main responsibilities of the first
detectors was to screen samples suspected of being infected with
soybean rust that were clearly infected with other foliar
diseases, not rust. However, because of the difficulty in
identifying soybean rust in the field, the function of the Fast
Track System was changed. First detectors no longer are asked to
filter out samples with other soybean diseases. The new role of
first detectors is to serve as a conduit to get samples
submitted properly to Iowa State University Plant and Insect
Diagnostic Clinic.
Update on fungicide labels
Only two Section 18 labeled foliar fungicides (PunchTM and
TopguardTM) remain for soybean rust treatment in Iowa and full
registration decisions are expected in 2009 for these products.
Alto®, CarambaTM, Folicur®, OriusTM, Quadris® Xtra and
UppercutTM had Section 18 labels for soybean rust and received a
full label for soybean in 2008. ProlineTM did not have a Section
18, but was registered for use on soybean in 2008. In 2009, the
active ingredient in ProlineTM is expected to be combined with
trifloxystrobin and marketed as Stratego Pro.
Daren Mueller is an extension specialist with
responsibilities in the Corn and Soybean Initiative.
This article was published originally on 12/1/2008 The
information contained within the article may or may not be up to
date depending on when you are accessing the information.
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