Soybean Rust Update- August 28, 2006
By Laura Sweets
Development and spread of soybean rust in the southern United States continues
to be slow. However, over the last few days soybean rust has been confirmed in
additional parishes in Louisiana and one county in South Carolina. According to
the USDA Public PIPE Website (www.sbrusa.net), soybean rust has been found on
this year's soybeans in sixteen different counties in six states (Alabama,
Florida, Georgia, Louisiana, Mississippi and South Carolina). The rest of the
positive reports for 2006 have been on kudzu. Recent shower activity has been
reported in some of the infected areas and local infection has increased in some
cases. Much like the 2005 season, more soybean rust finds are expected late this
season. However, harvest has started in many areas of the south so losses from
soybean rust for the 2006 season should be low.
In Missouri we are continuing to
monitor soybean rust sentinel plots.
Most of the sentinel plots have reached
the R4-R6 stage of growth. Thus far,
soybean rust has not been detected in
any samples submitted from sentinel
plots. As original sentinel plots reach R5-
R6 growth stage, observers are trying to
locate fields in earlier stages of growth to
monitor. Much of the state of Missouri
has also been unusually hot and dry so
conditions have not been favorable for
the development of soybean rust even
is spores had been introduced from the
southern United States. The southeastern
part of the state has had slightly better
precipitation so scouting in that part of
the state remains a priority.
In addition to the sentinel plot
program, the University of Missouri
is again participating in the Syntinel
RustTracker Spore Trap Network. This is
a soybean rust spore monitoring program
using spore traps designed to trap spores
and other particles present in air moving
through the spore traps. Spores and other
particles are trapped in petroleum jelly
coated on a microscope slide mounted
in the spore trap. The slides are removed
from the spore traps on a regular basis
and shipped to a central laboratory for
microscopic examination. Since the
spores of soybean rust aren't unique
enough to be distinguished from other
rust spores and even some other fungal
species, only tentative identification of
spores resembling those of the soybean
rust pathogen has been possible with this
spore trapping system.
There are two spore traps located
in Missouri, one in Boone County and
one in Ste. Genevieve County. The slide
from Ste. Genevieve County that was
microscopically examined on July 25
did have one spore which resembled a
soybean rust spore. The slide from the
Boone County location for the week of
August 1-8 did have three spores which
resembled those of soybean rust. Both
traps are located in sentinel plot fields
and soybean rust has not been found
on soybean plants in the sentinel plots
surrounding the spore traps. Plants at
both sites are at R4 stage of growth
and weather conditions have not been
favorable for rust infection nor disease
development.
Overall, because of continued low
levels of soybean rust inoculum to the
south, unfavorable weather conditions
in many parts of Missouri and the
advanced stage of growth of much of
the soybean crop, the risk for soybean
rust in Missouri remains low and
further management actions are not
necessary. Exceptions would be areas
of the state which have or are receiving
more normal rainfall and late planted or
double cropped soybean fields. Those
fields should be scouted on a regular
basis.
Bill Wiebold
573-882-0621
