Management of Soybean Rust Tristan Mueller Life Cycle

Management of Soybean Rust Tristan Mueller

Life Cycle • Uredinia produce urediniospores • Infect host • 9 -10 days to complete one cycle Uredinia Urediniospores

Soybean rust trials in FL Yield Loss • Potential to cause very large yield losses • Typically yield loss is greater the earlier rust is established in field • Rust spreads very quickly (especially within field) 9/25/2006 10/3/2006 11/17/2006 10/10/2006

Management of soybean rust • Resistance – no commercial varieties available Single site mode of action • Fungicides More systemic than strobilurins – Triazole Protectant and curative activity – Strobilurin Single site mode of action – Co-packs and Locally systemic premixes Protectant activity

Outline • What fungicides are available and how effective are they? • When is the best time to apply fungicides? • Can coverage of the soybean canopy be maximized using an air-assist sprayer? • Do we need to improve fungicide coverage to better manage soybean rust and improve yield?

Available Fungicides • Registered fungicides Active ingredient Product (trade name) azoxystrobin + propiconazole chlorothalonil myclobutanil Quadris Quilt Bravo, Echo, Equus Laredo EC, Laredo EW propiconazole + trifloxystrobin pyraclostrobin tetraconazole Tilt, Propi. Max, Bumper Stratego Headline Domark

Available Fungicides • Section 18 fungicides Active ingredient azoxystrobin + cyproconazole flusilazole flutriafol metconazole tebuconazole* tebuconazole + pyraclostrobin* Product (trade name) Quadris Xtra Alto Punch Topguard Caramba Folicur, Orius, Uppercut Headline SBR * Section 18 expired so availability will depend on renewal of exemption label – in progress

Fungicides in the Pipeline Active ingredient famoxadone + flusilazole* prothioconazole* tebuconazole + trifloxystrobin** Product (trade name) Charisma Not available Absolute * Decision expected in 2008 ** Decision depends on status of tebuconazole

Product Evaluation • Not all available fungicides evaluated in Florida • Most fungicides were very effective • Some products were better than others

Fungicide Timing When is the best time to apply fungicides?

Methods • Locations with rust (6 total) – South America (4) – Southern U. S. (2) • Fungicides – Headline (strobilurin) – Folicur (triazole) – Headline SBR (co-pack) – Quilt (premix)

Methods • Timing of application – Unsprayed control – Growth stage R 1, R 3, R 5 – R 1 + R 3 + R 5 • Data collected – Soybean rust severity – Defoliation – Yield – Seed weight

Yield vs. onset of disease • Fungicides were applied 47 days before to 36 days after rust was first reported • Pirapo and Capitan Meza: rust found at GS R 2 • Florida and Georgia: rust found at GS R 4 • Bella Vista (both years): rust found at GS R 5

Yield (bu/ac) Rust observed at GS R 2

Yield (bu/ac) Rust observed at GS R 4

Yield (bu/ac) Rust observed at GS R 5

Fungicide timing Conclusions • Best timing depends on when rust first infects soybeans and severity of infection • Early infection needs early fungicide application • Later infection the timing is less critical • Better to spray too early instead of too late • Fungicides may differ in sensitivity to timing

Florida Quilt Applications Yellow=GS R 1, Red=GS R 3, Blue=GS R 5, and White=non-sprayed control

Florida Headline SBR Applications Yellow=GS R 1, Red=GS R 3, Blue=GS R 5, and White=non-sprayed control

Air-Assist Sprayer Can fungicide coverage be maximized using an air -assist sprayer?

Methods • Urbana, IL • 2005 and 2006 • Air-assist sprayer (JACTO)

Methods • Air-assist blows air over the nozzle which helps propel drops into the canopy • Compared five nozzle types with and without air-assist Hollow cone Air Induction Ultra-Lo Drift Turbo Tee. Jet

Spray card setup • 18 Kromekote cards per plot • Placed at and canopy • Scan cards to determine percent coverage

2005 Air-assist results Air-assist Without Air-assist

2006 Air-assist results Air-assist Without Air-assist

Air-Assist Sprayer Summary • Less dense canopy – No advantage – Nozzles producing medium-sized drops resulted in the best percent coverage – All nozzles had about the same coverage in the lower canopy • Denser canopy – Better coverage, especially with smaller droplets – JA hollow cone nozzle with air-assist had the best coverage in the upper and lower canopy

Fungicide Coverage Do we need to improve fungicide coverage to better manage soybean rust and improve yield?

Methods • • Florida and Georgia, 2006 Pressures: 30, 50, and 70 psi Spray volumes: 10 and 20 gpa Nozzle types: Turbo Tee. Jet and Ultra Lo-Drift

Methods • Fungicide: Folicur (tebuconazole) • Data collected – Coverage in soybean canopy – Disease severity – Yield

Results – Coverage (spray volume) Upper canopy Lower canopy • 20 GPA treatments averaged twice the coverage of 10 GPA but resulted in equal amounts of fungicide that reached the cards

Results – Coverage (pressure) Upper canopy Lower canopy • In the upper canopy 70 psi typically had better coverage than 50 and 30 psi • In the lower canopy no differences in coverage among pressures

Results – Coverage (nozzle) Upper canopy Lower canopy • Turbo Tee. Jet had a slight increase in coverage in the upper canopy • In the lower canopy no differences in coverage between nozzles

Results – Soybean Rust • No difference among treatments sprayed with fungicides for rust severity • Non-sprayed control had higher rust severity than all of the treatments sprayed with fungicide

Results – Yield • No difference among treatments sprayed with fungicides for yield • For both locations, the non-sprayed control had the lowest yield

Fungicide Coverage Summary • 20 gpa had twice the coverage • 10 and 20 gpa results in equal amounts of fungicide on leaves • In general, 70 psi resulted in better coverage • No difference in disease severity or yield

Second Coverage Study • Florida, 2007 • Compare normal fungicide coverage with complete fungicide coverage • Normal = 15 gpa at 35 psi • Complete = 70 gpa with back pack sprayer (all leaves 100% covered)

Second Coverage Study • Still no differences

Take Home Message • Many fungicides work very well – some better than others • Timing of fungicides are critical for best management of soybean rust • Differences in coverage did not affect efficacy of fungicides

Acknowledgements • University of Illinois • University of Georgia – Dr. Glen Hartman – Dr. Carl Bradley – Dr. Loren Bode – Dr. Bob Kemerait • University of Florida – – Dr. Jim Marois Dr. David Wright G. Kelly O’Brien Maynard Douglas • RARS (Zimbabwe) – Dr. Clive Levy • CRIA (Paraguay) – Wilfrido Morel • USDA – Dr. David Walker