SOYBEAN RUST Phakopsora pachyrhizi

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SOYBEAN RUSTPhakopsora pachyrhizi

• G. L. Sciumbato, Plant Pathologist
• Delta Research and Extension Center
• Stoneville, MS

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Facts about the rust fungus

• Obligate parasite-Cannot survive unless it is in
  a host.
• Over 100 alternative legume hosts- Can complete
  life cycle on many legumes. Hosts include kutzu,
  crimson clover, white clover, sesbania, beans,
  peas etc.
• Rust spores can survive for up to 30 days outside
  a host and can travel up to 400 miles.

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Facts about the rust fungus

• Optimum growing temperatures 69-89O
• Fungal spores are sensitive to heat and die when
  temperatures are above 900
• Fungus grows best under moist conditions. Long
  dew periods etc. Dry, hot weather inhibits growth
  of fungus.
• Spores built up on host plants and are blown by
  wind currents to infect soybean plants.

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Facts about the disease on soybeans

• Can infect soybeans at most any growth stage
• Soybeans become more susceptible when they enter
  the reproductive stage (R1).
• No resistant varieties
• Causes premature defoliation, reduction in seed
  size and numbers
• Can cause up to 80 yield losses

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Where we are-What we know!

• Rust has been in China since 1902
• Rust a bigger problem in Southern China, much
  less of a problem in Northern China. (Spores
  travel from south to north each year)
• Rust found in Africa in 1996 and South America in
  1998.
• In South America, susceptible hosts present year
  around.

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Where we are-What we know!

• Rust has become a serious problem every year in
  parts of South America because susceptible hosts
  are present year around.
• Ninety percent plus of soybean acreage is
  treated with a foliar fungicide
• Rust carried by hurricane to the United States in
  November 2004.
• Rust found in late soybeans in most of the
  Southeastern United States. Also found in kitzu
  in Georgia and Florida.

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What we have done to prepare

• Training sessions have been and are being
  conducted on rust identification and control.
• Numerous educational materials have been
  developed to train personnel how to identify rust
• Section 18 registrations are being obtained to
  register fungicides for the rust control.

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What we have done to prepare

• A list of seven fungicides which have shown
  efficacy in controlling rust in South America are
  in the process of being approved for use in the
  United States.
• Other fungicides are being added to the list and
  are under the process of being registered.
• A program has been underway to breed soybeans for
  rust resistance. No resistant varieties are
  expected for 6-8 years.

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Next year-2005 growing season

• We do not know to what extent rust has infected
  alternative hosts in areas such as South Florida
  and the Caribbean where it can over winter.
• We have been unable to detect rust in many
  alternative hosts from these areas.
• Therefore, we believe that rust may or may not be
  a problem in the U.S. in 2005.

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Next year-2005 growing season

• Therefore, we are establishing Sentential plots.
  Sentential plots are small plantings of soybeans
  which are planted 2-3 weeks before the rest of
  the soybean crop is planted and monitored for
  rust. We hope to plant sentential plots along the
  Gulf Coast and up the Mississippi river. If rust
  is found in these plots, we will alert producers.

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Now What?

• Several different scenarios as to what will
  happen next have been proposed

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Scenario One-most probable

• Rust hosts die this winter in most of the United
  States. The fungus will over winter in hosts
  such as in South Florida or South Texas or in
  the Caribbean etc.
• This is similar to what happens in China and the
  fungus will have be carried by wind currents to
  the Southern United States and from then to the
  Northern soybean growing areas.
  

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Scenario One

• If this scenario happens, the severity of the
  disease would depend on wind currents etc and
  the disease would have to built up.
• If this scenario happens, the disease would be
  more severe in the Southern United States and
  would be a problem 1 or 2 years out of 5 in the
  Midwest and Northern United States

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Scenario Two-Unlikely

• The fungus is able to over winter in alternative
  hosts such as crimson clover, vetch in the United
  States.
• If this scenario happens, the disease would
  spread from the alternative hosts and rust would
  be a problem throughout the United States.
• This scenario is unlikely because the fungus does
  not over winter in China on alternative hosts.
  

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Scenario Three- Unlikely

• The fungus does not over winter in alternative
  hosts such as crimson clover, vetch in the
  northern hemisphere.
• If this scenario happens, the disease would have
  to be carried back into the United States by
  Hurricanes etc.

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Best Guess?

• Rust will probably not be severe in 2005 because
  the fungus has not built up in alternative hosts
  in areas where these hosts are not killed by
  winter. (South Florida, Caribbean, etc).
• Rust will built up in these areas and after 2005
  or 2006 rust will be blown into the Southern
  United States every year.

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Best Guess?

• Rust severity when this happens will depend on
  wind currents, temperature and moisture etc after
  the soybeans are planted.
• It will be possible to develop forecasting
  systems to predict rust severity etc.

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Rust Control and Management

• No resistant varieties for 6-8 years
• Cultural practices such as row spacing, seeding
  rates etc have little effect.
• We will have to depend on sentential plots and
  forecasting systems to identify and predict rust
  severity.
• Foliar fungicides will have to be used to manage
  rust.

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Foliar Fungicides to Control Rust

• Experience in Africa and South America has shown
  that 1-4 foliar fungicide applications beginning
  at the R1 growth stage are needed to manage rust.
• Fungicide labels will read that if you have 3-5
  rust infection, it is too late to spray
• Two main types of fungicides 1. Preventative or
  Protectant 2. Curative

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Foliar Fungicides to Control Rust

• Preventative fungicides such as Quadris and
  Headline have to be applied before rust
  infection.
• Curative fungicides such as Tilt, Folicur, Loredo
  etc. have some curative properties after rust
  infection.
• Mixtures of preventative and curative fungicides
  such as Stratego are also used.

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What to do?

• We are proposing the following options to
  producers
• 1. Plan on applying a foliar fungicide at R1 and
  R3. If rust is present use a curative fungicide.
• 2. Monitor the sentential plots and apply a
  fungicide when rust is detected. If this method
  is used you run the risk of missing rust
  infections and not applying the fungicide soon
  enough.

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What to do?

• 3. Wait until rust is detected and spray. This
  is very risky because rust is hard to detect.
• If you do not have to spray until R3, or for the
  R5 spraying, it is recommended that a fungicide
  such as Quadris, Headline, or the mixture
  Stratego be used. The reason for this is that
  these fungicides control other late season
  diseases and the control of these diseases will
  help defray fungicide costs.

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STROBILURINS

• PREVENTATIVE ACTION ONLY-cannot be applied after
  disease is present.
• VERY EFFECTIVE IN PREVENTING DISEASE DEVELOPMENT.
• DEPENDING ON DOSAGE CAN PROVIDE LONG PERIODS OF
  DISEASE CONTROL
• CANOPY COVERAGE CRITICAL.
• CONTROL A NUMBER OF OTHER DISEASES.

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QUADRIS (Syngenta)

• Common name AZOXYSTROBIN
• Preventative action only.
• Potential for resistance to develop.
• Depending on dosage, active for several weeks.
• Use rate 6.2 oz/A. Can be up to 15.4 oz/A.
• Cost per acre for each application12.89 for
  fungicide 3.90 ground or 5.47 aerial
  applications costs.

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HEADLINE (BASF)

• Common name Pyraclostrobin
• Recommended as a preventative, has some systemic
  activity.
• Potential for resistance to develop.
• Not quite as long lived as Quadris.
• Use rate 6.0 oz/A. Can be up to 12 oz/A
• Cost per acre for each application10.83 and up
  for fungicide 3.90 ground or 5.47 aerial
  applications costs.

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TRIAZOLES

• Primarily Preventative action but can have some
  curative activity.
• Some are very systemic and therefore spray
  coverage not as important.
• Some are short lived.
• No resistance to trizoles confirmed.
• Control some other diseases.
• Often mixed with other fungicides to manage
  fungicide resistance.

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TILT, BUMPER, PROPIMAX(Syngenta, Dow, etc.)

• Common name PROPICONAZOLE.
• Has curative activity
• Short lived
• Often mixed with other fungicides.
• Use rate 4.0 oz/A. Can be up to 8 oz/A
• Cost per acre for each application10.16 and up
  for fungicide 3.90 ground or 5.47 aerial
  applications costs.

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FOLICUR (Bayer)

• Common name TEBUCONAZOLE.
• Has some curative activity.
• Looks good in trials in South America.
• Very systemic.
• Use rate 4.0 oz/A.
• Cost per acre for each application10.47 for
  fungicide 3.90 ground or 5.47 aerial
  applications costs.

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LOREDO, SYSTHANE (Dow)

• COMMON NAME MYCLOBUTANIL.
• Has some curative activity.
• Systemic.
• Use rate 4.0-8.0 oz/A.
• Cost per acre for each application5.75 and up
  for fungicide 3.90 ground or 5.47 aerial
  applications costs.

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DOMARK (Valent)

• Common name TETRACONAZOLE.
• Has some curative activity.
• Systemic. Looks good in South America.
• Use rate 10.0-13.0 oz/A.
• One of original seven to be granted a section 18
  label when rust was found.
• Soybean registration pending.
• Cost per acre for each application12.42 and up
  for fungicide 3.90 ground or 5.47 aerial
  applications costs.

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CARAMBA (Bayer)

• Common name METCONAZOLE.
• Has some curative activity, systemic.
• Registration to be submitted in Feb.
• Use rate unknown.
• May also be premix with Headline
• Cost per acre for each application unknown
  3.90 ground or 5.47 aerial applications costs.

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PUNCH (Dupont)

• Common name FLUSILAZOLE.
• Has some curative activity, systemic.
• Registration to be submitted in Feb.
• Use rate unknown.
• Also premix with famoxadone (Charisma)
• Cost per acre for each application unknown
  3.90 ground or 5.47 aerial applications costs.

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IMPACT (CHEMINOVA)

• Common name FLUTRIAFOL.
• Has curative activity, systemic.
• Registration to be submitted in ?.
• Use rate unknown.
• Has looked good in South America
• Cost per acre for each application unknown
  3.90 ground or 5.47 aerial applications costs.

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ALTO (SYNGENTA)

• Common name CYPROCONAZOLE.
• Has curative activity, systemic.
• Registration to be submitted in Feb.
• Use rate unknown.
• Has looked good in South America
• Also premix with Quadris Quadris Extra
• Cost per acre for each application unknown
  3.90 ground or 5.47 aerial applications costs.

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JAU6476 (BAYER)

• Common name is PROTHIOCANAZOLE.
• Has curative activity, systemic.
• Registration to be submitted in Feb.
• Use rate unknown.
• Also premix with Trifloxystobin
• Cost per acre for each application unknown
  3.90 ground or 5.47 aerial applications costs.

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OTHER FUNGICIDES-BRAVO, EQUUS, ECHO (Syngenta,
etc.)

• Common name CHLOROTHALONIL.
• Protectant activity only
• Short lived
• Not as effective as other fungicides
• Use rate 1 1/3 pt 2 ¼ pt/A
• Cost per acre for each application 7.20 and
  up for fungicide 3.90 ground or 5.47 aerial
  application costs.

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FUNGICIDE MIXES

• Two modes of action- reduces chances of
  resistance to fungicide building up.
• Broader spectrum of activity.

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STRATEGO (Bayer)

• Mixture of trifloxystrobin propiconazole
• Use rates of both fungicides are lower than when
  the fungicide is used alone.

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PRISTINE (BASF)

• Mixture of pyraclostrobin boscalid
• One of original seven to be granted a section 18
  label when rust was found
• Boscalid has little activity on rust.
• Not registered on soybeans.

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QUILT (Syngenta)

• Mixture of azoxystrobin proponazole
• Use rates of both fungicides are lower than when
  the fungicide is used alone.
• Registration will be submitted in February.

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Some Final thoughts

• It is an advantage to grow short season varieties
  (IV and early V) because fewer fungicide sprays
  are needed.
• It may be an advantage to plant early because the
  early planted beans are maturing in July and
  August when it is hot and weather conditions are
  not favorable for rust development.

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Some Final thoughts

• Rust is manageable, however rust control will add
  30-50 per acre to the cost of growing soybeans.
• Rust control must began before the disease is
  severe in your field.
• Rust has been managed in other areas where it is
  present and it can be managed in the United
  States.