Knoxville, Tennessee
October 8, 2007
Experts with
University of Tennessee
Extension have documented the presence of Asian soybean rust in
the state. A significant agricultural disease, Asian soybean
rust was found in West Tennessee on soybean leaf samples
collected by Dr. Angela Thompson, UT Extension soybean
specialist, from a field plot in Gibson County at the UT Milan
Research and Education Center on Wednesday, October 3.
In a year when weather has plagued Tennessee producers with both
an early freeze and an extended drought, farmers were fortunate
that the disease did not occur until the end of the growing
season when most soybeans are nearing maturity and many have
already been harvested.
UT Extension plant pathologist Beth Long says the disease caused
no damage to Tennessee's soybean crop this year. “Most soybean
plants in Tennessee have been harvested and very little green
leaf tissue remains in the field,” she said.
However, this year’s crop has not fared well. Soybeans generally
rank among the state's top crops, earning farmers approximately
$278 million in cash receipts in 2006. Due to the drought, this
year’s harvest is significantly diminished. Yields are down from
39 bushels per harvested acre in 2006 to estimates of just 24
bushels per acre this year. The Tennessee Agricultural
Statistics Service reported in September that production for
2007 is expected to have fallen by 57 percent from last year’s
44 million bushels to just 25.2 million bushels this year.
UT Extension monitored for rust in soybean sentinel plots and
spore traps across the state all summer and only found these few
rust lesions on soybean leaves last week. The disease samples –
a few rust pustules – were found on soybean leaves and visually
identified with a microscope at the UT Extension lab at Jackson.
The samples were then tested with the "QuickStix"
method by Dr. Melvin Newman, UT Department of Entomology and
Plant Pathology, in Jackson. The leaves are undergoing final
confirmation that the pustules are Asian soybean rust by
polymerase chain reaction (PCR) testing in Dr. Kurt Lamour's lab
at UT Institute of Agriculture in Knoxville.
Dr. Newman speculates that the lack of rain in West Tennessee
during critical times in the growing season prevented soybean
rust from developing earlier. "Several rain fronts passed by
West Tennessee, but they developed and caused rain west of the
Mississippi River. This may be why soybean rust was found in
Eastern Arkansas in late September while none was found in
Tennessee until last week," he said. Soybean rust has been found
in neighboring states including Arkansas, Alabama, Mississippi
and Kentucky.
Because soybean rust is spread primarily by wind-borne spores
and is capable of being transported over long distances, no
regulatory action will be taken. Although soybean rust cannot
survive the winter in Tennessee, rust spores can easily be blown
in during the growing season from areas in the Southern U.S.
where freezing temperatures do not occur.
Growers should contact their local county UT Extension agent to
discuss preventative and control measures for next year.
Asian soybean rust is caused by the fungal species Phakopsora
pachyrhizi and is known to infect kudzu and many other legume
species. It has the potential to significantly reduce soybean
yields but can be managed with the use of fungicides if detected
early.
At this time there are no commercial soybean varieties resistant
to soybean rust. Prevention and control measures are expected to
raise costs for producers and ultimately for consumers.
Fungicide applications can reduce yield losses from rust and
other late-season diseases, depending on the plants'
developmental stage, the time during the growing season when
soybean rust is detected and weather conditions.
In addition to this West Tennessee site, Asian soybean rust has
been found in 15 states in 169 counties; in 18 counties in
Alabama (13 soybean), 33 counties in Arkansas (all soybean), 16
counties in Florida (eight soybean),
14 counties in Georgia (10 soybean), one county in Illinois
(soybean), one in Iowa, four counties in Kansas (soybean), two
counties in Kentucky (soybean), 15 parishes in Louisiana (14
soybean), 15 counties in Mississippi (twelve soybean), four
counties in Missouri (soybean); two counties in Nebraska
(soybean); 11 counties in Oklahoma (all soybean), seven counties
in South Carolina (soybean) and 26 counties in Texas (25
soybean).
More information about soybean rust and recommended measures for
controlling the disease are available through the UT Extension
Web site: http://UTcrops.com.
First click on "soybean" then follow the link labeled "diseases
and nematodes."
Growers can also visit the USDA
soybean rust Web site:
http://www.sbrusa.net/ and view the map showing positive
locations.
UT Extension offices are listed in local phone books under the
county government listing. Additional information is available
online at:
http://www.utextension.utk.edu/offices
This is the first instance of Asian soybean rust found in
Tennessee during 2007. There were no finds of this disease
during the 2005 growing season, however it was found in West and
Middle Tennessee during late October 2006, immediately before a
heavy frost. Asian soybean rust was first found in the United
States in November 2004. The disease was confirmed at that time
in samples across nine southern states, including one sample
from Shelby County, Tennessee. |
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