Ames, Iowa
September 28, 2007
Iowa State University has confirmed the presence of soybean
rust infection from plant samples taken this week from a field
in Dallas County.
“We knew this discovery was a real possibility because of the
spore delivery from the south,” said Bill Northey, Iowa
Secretary of Agriculture. “The good news is that since it is so
late in the growing season, spraying is not necessary and any
infection would not be expected to reduce yields.”
This is the first confirmed case of the disease found during the
growing season in Iowa. But Iowa State plant pathologists
stressed that the discovery coming so late in the growing season
is fortunate timing for soybean growers.
Extension plant pathologist X.B. Yang said soybean rust will not
reduce soybean yields if infections occur after the soybean crop
has reached the full-seed developmental stage, referred to as
R6.
“Applying foliar fungicides for control of soybean rust after
the crop has reached the R6 stage likely will not provide an
economic benefit in terms of yield protection,” said Yang. “The
seeds have fully formed at this stage and need only to mature
before harvest.”
Recent cases of rust infection also have been discovered in
Illinois, Kansas and Missouri. The disease is spread from
southern states by wind and air currents. Its discovery this
late in the season fits within air current models.
The Iowa Soybean Rust Team -- which includes representatives of
Iowa State, Iowa Department of Agriculture and Land Stewardship,
the Iowa Soybean Association and the USDA Animal and Plant
Health Inspection Service -- have recommended not spraying
soybeans with fungicide once the crop has reached the full-seed
stage.
Also, application of foliar fungicides this late in the growing
season may be illegal because it exceeds the minimum pre-harvest
interval, the time between the last application of a pesticide
to a crop and when the crop may be harvested.
After a report that a soybean leaf with rust-like pustules had
been found, Yang collected hundreds of leaf samples from the
area around the Dallas County field. Subsequent testing in the
ISU Plant and Insect Diagnostic Clinic confirmed the presence of
soybean rust.
The fungus and spores that cause the disease cannot survive an
Iowa winter, plus they require green leaf tissue to sustain
themselves. That is why any treatment of late-season soybean
rust infections in Iowa would be unnecessary and not impact the
overwinter survival of the fungus. Also, the fungus cannot
survive on grain or seed.
The Iowa Soybean Rust Team has recruited and trained more than
600 agribusiness professionals around Iowa to be “First
Detectors” who can examine leaf samples and decide whether they
warrant further analysis by ISU extension specialists or faculty
scientists to detect possible infection.
Soybean growers have been encouraged to work with First
Detectors and consult with ISU Extension specialists on
identification and management plans. Names and contact
information for First Detectors are available on the Iowa
Soybean Rust Team's Soybean Rust website, www.soybeanrust.info <http:www.soybeanrust.info>,
and at county ISU Extension offices.
Soybean rust infections in counties throughout the United States
can be tracked at the following USDA website,
www.sbrusa.net.
Training efforts also continue. Earlier in September, 33 ISU
personnel and Iowa agribusiness professionals attended a
hands-on training program on soybean rust identification and
management at a University of Florida research and education
site. The trip was organized by Iowa State’s Corn and Soybean
Initiative and sponsored in part by soybean checkoff funds from
the Iowa Soybean Association and funds from the USDA National
Plant Diagnostic Network.
RELATED RELEASE
Urbandale, Iowa
September 28, 2007
Asian soybean rust found in Iowa
soybean field
The Iowa Soybean Association
(ISA) cautions Iowa soybean producers to be vigilant in the next
few weeks as late-planted soybeans reach maturity. Asian rust
was found in a soybean field in Dallas County on Tuesday,
September 25. The disease was confirmed using molecular
techniques conducted by a reputable company. The presence of
soybean rust was also confirmed by Dr. X. B. Yang, plant
pathologist, Iowa State University, one of the world’s experts
on Asian soybean rust.
“This is an important find for Iowa soybean growers,” says Curt
Sindergard, Iowa Soybean Association president and a soybean
grower from Rolfe. “It confirms that soybean rust can develop in
Iowa. We are fortunate that this disease was found at a time
when it will have little economic impact for soybean producers.”
Soybean rust could cause damage to Iowa’s late-planted soybeans.
Early planted soybeans may be less at risk if they are at the R6
growth stage or later. After R6, there appears to be no economic
advantage to treating fields with fungicides according to Dr.
David Wright, ISA director of contract research. R6 is defined
as: full seed – pods contain green seed that fills the pod
capacity at one of the four uppermost nodes on the main stem.
“We recommend that soybean growers scout fields with soybeans at
the R4 to R6 growth stages to determine their overall risk,”
says Wright. “Most Iowa soybean fields are likely mature enough
that producers need not spray this season.”
Wright also says soybean producers should be acutely aware that
fungicides have a pre-harvest interval during which growers
should not harvest fields. Be sure to consult your crop advisor
before applying fungicides.
“Scout late-planted fields first, particularly those that retain
moisture from morning dew,” says Wright. “First, determine
soybean growth stage. Then look for infected leaves in the lower
canopy. Look at the underside of lower leaves for small
volcano-like structures. The opening of these structures will be
round, not linear. A 20-30X hand lens is recommended.”
ISA and Iowa State University have partnered to train more than
650 agricultural professionals to serve as First Detectors.
These people have been trained to identify soybean rust and are
part of a nationwide effort to minimize the impact of rust. You
can find your local First Detector by logging on to
www.soybeanrust.info and entering your ZIP code. Or check with
your local certified crop advisor to determine if they’ve been
trained by Iowa State University as a First Detector for soybean
rust.
If you suspect you have found rust in your soybean fields, call
your local First Detector or send a plant sample to the Crop and
Diagnostic Clinic, 351 Bessey Hall, Iowa State University, Ames,
IA 50011.
To learn more about soybean rust, visit the ISA Web site,
www.iasoybeans.com and
click on “production research.”
The Iowa Soybean Association develops policies and programs
that help farmers expand profit opportunities while promoting
environmentally sensitive production using the soybean checkoff
and other resources. The Association is governed by an elected
volunteer board of 21 farmers.
Funded by the soybean checkoff
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