Manhattan, Kansas
September 21, 2007
For the first time ever, Asian
soybean rust has been confirmed in a Kansas soybean field.
Kansas State University
researchers and the Kansas Department of Agriculture have
confirmed that a leaf sample from a soybean plant collected from
a sentinel plot in Montgomery County has the disease.
"Asian soybean rust´s arrival in Kansas was expected," said
Kansas Secretary of Agriculture Adrian Polansky. "And, we must
continue to be vigilant, scouting for this disease in the coming
years, to ensure we detect it early enough for growers to take
action to protect their crops."
The site where the positive sample was found is one of 20 that
the U.S. Department of Agriculture, working with KDA and
K-State, planted around Kansas to monitor for the disease.
"For this year, this will only be a problem in late-planted
soybeans," said Kansas State University plant pathologist Doug
Jardine. "There are 300,000 to 400,000 acres of late-planted
soybeans this year that are potentially in danger. This
represents about 10 to
15 percent of the state´s crop."
In university research trials during the 2005 and 2006 growing
seasons, measured yield losses to soybean rust ranged from 6 to
32 percent, Jardine said. He anticipates that any potential
yield loss in Kansas this year in the late-planted bean crop
would likely be at the lower end of this range.
Soybean rust was first found in the United States Nov. 6, 2004,
in Louisiana. Since then, it has spread to several states.
The disease is caused by either of two fungal species -
Phakopsora pachyrhizi, also know as the Asian species, and
Phakopsora meibomiae, the New World species. The Asian species
is the more aggressive of the two and causes more damage to
soybean plants, said Jardine, who is the plant pathology state
leader for K-State Research and Extension.
The disease is spread by wind-borne spores capable of being
transported over long distances. Asian soybean rust was first
observed in Japan in 1902 and was found throughout most Asian
countries and in Australia by 1934.
Any soybean field that has reached the R6 stage of development
(full pod fill) is no longer in danger from the disease, Jardine
said.
Decisions to apply a fungicide on fields that have not reached
that growth stage need to be made on a field-to-field basis.
K-State Research and Extension has developed a calculator
spreadsheet to assist producers in making the decision whether
to spray. It is available on the AgManager Web page at
www.agmanager.info as
"Economics of spraying soybeans" or accessible directly at:
http://www.agmanager.info/crops/prodecon/production/decision/default.asp.
The decision to spray is dependent on a combination of growth
stage, application costs, expected selling price and the yield
that will be saved by spraying. Given the level of disease
currently being found, yield savings would likely be no more
than about 10 percent.
If a fungicide application is deemed necessary, producers are
encouraged to use a triazole fungicide because the mode of
action will have some curative effects on infections already in
progress.
Triazole fungicides currently labeled for use on soybean rust in
Kansas include Alto, Caramba, Domark, Folicur, Laredo, Punch,
Tilt and Topguard.
Growers can access information about fungicides currently
registered for use in Kansas from the Kansas Department of
Agriculture Web site at
www.ksda.gov/pesticides_fertilizer/content/288.
"To scout for soybean rust, you should arbitrarily collect or
observe a minimum of 100 leaflets from the lower canopy (older,
main-stem terminal leaflets) in each field," Jardine said.
"Areas of the field that may be shaded, especially from the
morning sun, are good places to look for rust.
"To observe pustules, a minimum 20X hand lens is needed, but 30X
is better. Pustules will be found on the bottom side of the
leaflets and have the appearance of small volcanoes within the
lesion."
Scouting currently is more difficult in many areas of the state,
due to the presence of two other similar-looking diseases: brown
spot and bacterial blight, Jardine acknowledged.
For photos and further information on the disease´s symptoms,
Jardine encourages growers to view a University of Missouri Web
site:
http://www.extension.missouri.edu/explorepdf/agguides/crops/g04442.pdf
Producers or scouts can submit samples of suspect soybean leaves
for evaluation at K-State through any county or district
Cooperative Extension Service office, Jardine said. He
recommended:
- Send 10-15 suspect leaves.
- Place the leaves in a
zipper-style plastic bag with a tight seal, and put that bag
in a second such bag. Seal both bags securely.
- Attach a note or write on
the outer bag that this is a soybean rust sample.
- Do not add wet paper
towels or other types of moisture to the bag.
- Try to mail it in the
Monday-Wednesday time frame to avoid the possibility of the
samples´ spending the weekend in a hot post office loading
area.
Soybean growers and industry
people can track the spread of soybean rust on the USDA Legume
PIPE Web site at www.sbrusa.net . This site also contains weekly
commentaries from Extension specialists in each state on crop
growth and development, disease progress, scouting, and
fungicide application recommendations.
Additional information on soybean rust can also be found on the
Plant Management Network´s Soybean Rust Information Center at
http://www.plantmanagementnetwork.org/infocenter/topic/soybeanrust/.
K State Research and Extension is a short name for the Kansas
State University Agricultural Experiment Station and Cooperative
Extension Service, a program designed to generate and distribute
useful knowledge for the well being of Kansans. Supported by
county, state, federal and private funds, the program has county
Extension offices, experiment fields, area Extension offices and
regional research centers statewide. Its headquarters is on the
K State campus in Manhattan. |
|
