Fungicides and Their Time of Application for the Control of Soybean Rust

Tristan Mueller

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

10/10/200611/17/2006

Soybean rust trials in FL

Management of soybean rust

• Resistance– no commercial varieties

available

• Fungicides– Triazole– Strobilurin– Co-packs and

premixes

Single site mode of actionMore systemic than strobilurinsProtectant and curative activity

Single site mode of actionLocally systemic Protectant activity

• Not all available fungicides evaluated in Florida

• Most fungicides were very effective• Some products were better than others

Product Evaluation

Outline

• When is the best time to apply fungicides?

• Soil applied fungicides?

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 R1, R3, R5– R1 + R3 + R5

• 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– GS R5 epidemic with GS R1 fungicide

application– GS R2 epidemic with GS R5 fungicide

application

• Pirapo and Capitan Meza: rust found at GS R2

• Florida and Georgia: rust found at GS R4

• Bella Vista (both years): rust found at GS R5

Rust observed at GS R2

0

5

10

15

20

25

30

Pirapo Capitan Meza

ControlR1R3R5MaxYi

eld

(bu/

ac)

Rust observed at GS R4

01020304050607080

Florida Georgia

ControlR1R3R5MaxYi

eld

(bu/

ac)

Rust observed at GS R5

05

101520253035404550

Bella Vista (2005) Bella Vista (2006)

ControlR1R3R5MaxYi

eld

(bu/

ac)

Fungicide timing

• 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

Conclusions

Florida Quilt Applications

White=non-sprayed control, Yellow=GS R1, Red=GS R3, and Blue=GS R5

YieldCon=42 bu/aR1=45 bu/aR3=46 bu/aR5=50 bu/a

Florida Headline SBR Applications

YieldCon=42 bu/aR1=46 bu/aR3=58 bu/aR5=62 bu/a

White=non-sprayed control, Yellow=GS R1, Red=GS R3, and Blue=GS R5

Fungicide Efficacy

• Quilt still protected yield to some extent, but not as effectively as Headline SBR

• With more severe rust severity fungicide selection becomes more important

Soil applied fungicides

Soil applied fungicides?

Soil applied fungicides-2006

•The higher the rate generally better the control•Some treatments not different than a foliar applied fungicide

Soil applied fungicides-2007

•The higher the rate generally better the control•All treatments better than the non-sprayed control•Some treatments not different than a foliar applied fungicide

• With the fungicide Topguard a soil applied fungicide protected soybean leaves from rust for most of the season

• Many of the treatments were no different than a foliar applied fungicide

Soil applied fungicides

Take Home Message

• Many fungicides work very well – some better than others

• Timing of fungicides are critical for best management of soybean rust

• Soil applied fungicides (Topguard) may be a method to control soybean rust

Acknowledgements• University of Florida

– Dr. Jim Marois– Dr. David Wright– G. Kelly O’Brien– Maynard Douglas

• University of Illinois– Dr. Glen Hartman – Dr. Carl Bradley – Dr. Loren Bode– Dr. Monte Miles

• University of Georgia– Dr. Bob Kemerait

• RARS (Zimbabwe)– Dr. Clive Levy

• CRIA (Paraguay)– Wilfrido Morel

Questions?