Positive Developments in Soybean Rust Research Presented at 2007 National
Soybean Rust Symposium
Since the arrival of the soybean rust pathogen in North America only
three years ago, there has been an unprecedented amount of collaboration
among producers, industry, scientists, USDA, extension staff, crop advisors,
and soybean check-off organizations to understand Asian soybean rust
and to mitigate its impact on soybean production in the United States.
The positive results of this effort were clear as leaders in soybean
rust research and extension shared their experiences and research results
on Dec. 12-14 in Louisville, Ky.
The notable achievements of this nationwide, grassroots effort are many.
In only three years, cooperators have established a real-time tracking
system for soybean rust called the USDA Plant Information Platform for
Extension and Education (PIPE), the sentinel plot system, a spore tracking
system, and climate-based epidemiological models that feed into it.
More than 475 people were involved in the sentinel plot system in 2007,
and more than 13,412 observations were uploaded to the PIPE Web site.
This represents an enormous amount of cooperative work.
Knowing when and where rust is found – and whether environmental
conditions are present that will favor it – are key factors for
deciding when to spray and when to wait. If one considers how many acres
might have been sprayed unnecessarily if none of this information was
available, you can see the huge environmental benefit as well as money
saved from this information network.
Regarding soybean rust control, the reports on fungicide trials held
in two U.S. and four South American locations in 2007 were positive.
Most fungicides tested were reported to be "very effective"
in controlling Asian soybean rust. Only when disease pressure was very
high did some products perform better than others. The researchers confirmed
that good coverage into the mid- and lower canopy is critical, as well
as the timing of the fungicide application — especially if soybeans
are still in early growth stages.
The risk of fungicide resistance was also discussed, and there was some
good news in this area as well. Although fungi can and do develop resistance
to the triazole and strobilurin fungicides used for soybean rust, there
are factors about the U.S. situation that helps lower the risk. One
is that Phakopsora pachyrhizi, the soybean rust pathogen, does not overwinter
in most soybean production areas of the United States and another is
that only one or two, if any, sprays are needed each season.
Ultimately, as with all rust diseases, it will be the employment of
resistant soybean varieties that will provide the most effective and
stable long-term control of Asian soybean rust. Soybean breeders and
plant pathologists are now in their third year of field-testing resistant
soybean germ plasm in the United States. This year they evaluated 703
soybean lines in seven different locations and reported a clear sorting
of resistant reactions compared to susceptible soybean varieties. Several
genes for resistance have been identified.
Asian soybean rust was found in 19 states and 301 counties (thought
to be a conservative estimate) in 2007. Although disease pressure was
high in some southern areas, notably Alabama, Louisiana, and Georgia,
it was generally held in check by widespread freezing temperatures in
the South during April that reduced the amount of spores, and also by
the 2007 drought. The northernmost find in the United States was in
Hancock County, Iowa, in October. By November it was also detected for
the first time in Ontario, Canada.
