Soybean Diseases in Arkansas
Asian Soybean Rust
Questions and Answers - by Chris Tingle
The following Questions were collected by Chris Tingle at a
meeting with LSU Extension on November 17, 2004 at Baton Rouge :
What will the fungicide options be?
Section 18 labels have been approved for Laredo ,
Tilt, Propimax, Bumper and Folicur. Pending are Pristine, Domark and Stratego.
Headline is pending a Section 3 (full) label for soybeans. Quadris already has a
Section 3 label as does Bravo and Echo (chlorothalonil).
What types of fungicides are these?
Tilt, Propimax, Bumper (all propiconazole),
Folicur (tebuconazole) and Laredo (mycobutanil) and Domark (tetraconazole) are
all triazoles that are locally systemic and have some curative activity against
rusts. Quadris, Pristine and Headline are strobilurins and offer mostly
protectant (pre-infection) activity but they are also locally systemic. Bravo
and Echo are protectants with no systemic properties.
What is the timing for fungicides to control soybean rust?
Early R stages not as effective in some areas of
the world with R3 giving better control depending on the availability of spores
and environment. In South Africa , 2 applications with the first 70 days after
planting gave the highest yields of the timings tried.
What about fungicides and other diseases?
Headline, Quilt, Pristine all appear to have good
activity on frogeye and cercospora leaf blight; Headline and Quadris appear to
be good on aerial blight.
What is the treatment threshold for soybean rust?
In other countries, some use a general threshold
of less than 3-5% for protectants and less than 10% for triazoles.
Is there a danger of fungicide resistance with soybean rust?
Yes, and strobilurins and triazoles will need to
be rotated and possibly only a single application of each per season to avoid
resistance.
Are forecast models an option?
Yes, they may be and are being developed.
What about early vegetative damage? Should we spray before
flowering if the disease is active?
You may see symptoms prior to flowering but it
should not cause yield loss if fungicides are applied at the proper reproductive
stages.
Not all of the 2004 soybean crop has been harvested. What
should we do now?
Don't worry, frost will take care of the rust
this year and drive it further south.
What about overwintering on alternate hosts?
Other plant species are susceptible but not
preferred by the fungus but they may serve as an inoculant for next year.
How fast can soybean rust move north?
Reported 300 miles per day.
Crop Insurance will consider this a natural disease, will it
cover damage?
If a producer files a claim due to soybean rust,
he must prove that he purchased and applied recommended products and rates in
order to collect benefits.
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Asian Soybean Rust
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