Validation, Optimization, and Deployment of Fungicide Advisories for Soybean

Virginia Soybean Board

2014 Project Report & 2015 Project Proposal

Dr. Hillary L. Mehl, Plant Pathologist

Dr. David Holshouser, Soybean Agronomist

Tian Zhou, MS Student

Virginia Tech Tidewater AREC

March 12, 2015

Integrated Disease Management - Soybean

• Know your target disease so you can select the best cultivar and fungicide – foliar fungi

• Plant resistant/tolerant cultivars (or be aware of susceptibility to specific diseases)

• Optimize fungicide timing and chemistry for target disease

Do Foliar Fungicides Pay?Points to Consider

• How susceptible or resistant is your cultivar?

• Yield potential – what are you protecting?

• Crop growth stage and timing of fungicide

applications

• Previous crop and cropping system (e.g. no till)

• Disease pressure

• Weather

2014 Objectives

1. Validate and optimize a weather-based disease advisory model for timing of foliar fungicide application in soybean

2. Evaluate profitability of different fungicide spray schedules based on yield response and input costs

3. Initiate development of a web-based disease advisory alert system for soybean

Fungicide Spray Window

Fungicide Spray Window

Growth stage-based fungicide applications

Foliar disease risk model:“Favorable days” for disease development

Soybean Weather-Based Fungicide Advisory: Validation Trials 2014

Eastern Virginia AREC (Warsaw)

Tidewater AREC (Suffolk)

R3 FungicideAdvisory Fungicide

No Fungicide

7 on-farm trials2 small plot studies (ARECs)

*

*

*

**

**

* Weather station

Treatments

Fungicide timing vs yield response

R3

Adviso

ry 1

spr

ay*

1 wee

k af

ter R

3

2 wee

ks a

fter R

3

3 wee

ks a

fter R

3

4 wee

ks a

fter R

3

R3 & 2

1 da

ys a

fter R

3

Adviso

ry 2

spr

ays*

Wee

kly s

pray

s be

twee

n R3

and

R5100

110

120

130

5.1 bu/A0.2 bu/A

7.0 bu/A5.3 bu/A2.7 bu/A

11.6 bu/ATAREC EVAREC

Fungicide application timing

% y

ield

re

sp

on

se

c

om

pa

red

to

un

tre

ate

d

Single application

Multiple applications

Each % yield response = 0.6 bu/A

TAREC (Suffolk) – Cercospora blight

*Weather advisory and growth stage-based sprays were made on the same date

EVAREC (Warsaw) – Frogeye leaf spot

County Variety TreatmentSpray Date Fungicide & Rate Yield (bu/A)

Orange Asgrow AG4633 Control NA   47.4 B

    R3 July 29 Priaxor - 4 oz/A 52.6 A

    Decision Aid Aug 4 Priaxor - 4 oz/A 52.0 A

Culpeper NK S41-J6 Control NA   61.0 A    R3 Aug 11 Priaxor – 4 oz/A 59.7 A

    Decision Aid Aug 20 Priaxor – 4 oz/A 57.2 AStafford Pioneer P39T67 Control NA   67.8 A    R3 Aug 7 Quadris Top - 11 oz/A 69.7 A

    Decision Aid Aug 16 Quadris Top - 11 oz/A 70.2 AAmelia Armor 5363 Control NA   41.4 C

    R3 Aug 15 Quadris Top – 10 oz/A 47.7 A

    Decision Aid Aug 20 Quadris Top – 10 oz/A 46.1 BNottoway   Control NA   45.4 B

    R3 Sept 16   46.7 A

    Decision Aid Sept 26   46.7 ASussex Hubner H53-12R2 Control NA   30.0 B

    R3 Sept 3 Stratego YLD – 6 oz/A 34.2 A

    Decision AidSept 16 (Sept 9) Stratego YLD – 6 oz/A 32.7 A

Accomack Channel 4206 Control NA   54.7 A

  & 4306 R3 Sept 11 Stratego YLD – 4 oz/A 53.6 A

    Decision Aid Sept 15 Stratego YLD – 4 oz/A 48.8 A

“Favorable days” vs yield response

4 5 6 7 8 9 10 11 12 13 1490

95

100

105

110

115

120

R² = 0.978270057905727R² = 0.942115792304356

R3

#of days between R3 growth stage and favorable days for disease

Yie

ld (

% o

f u

ntr

eate

d c

on

tro

l)

+1-2 bu/A

+4-6 bu/A

Yield response needed to offset cost of fungicide application in soybean

Treatment cost/A

Soybean price/bu

$9 $10 $11 $12 $13 $14

$15.00 1.7 1.5 1.4 1.3 1.2 1.1

$17.50 1.9 1.8 1.6 1.5 1.3 1.3

$20.00 2.2 2.0 1.8 1.7 1.5 1.4

$22.50 2.5 2.3 2.0 1.9 1.7 1.6

$25.00 2.8 2.5 2.3 2.1 1.9 1.8

$27.50 3.1 2.8 2.5 2.3 2.1 2.0

$30.00 3.3 3.0 2.7 2.5 2.3 2.1

$32.50 3.6 3.3 3.0 2.7 2.5 2.3

$35.00 3.9 3.5 3.2 2.9 2.7 2.5Favorable days for disease development:< 8 days after R3 4-6 bu/A yield response> 8 days after R3 1-2 bu/A yield response (or less)

Virginia Ag Pest and Crop Advisory Blog

http://blogs.ext.vt.edu/ag-pest-advisory/The weather-based advisory needs to be further validated, but preliminary fungicide advisories for soybean will be posted on the Virginia Ag Pest and Crop Advisory Blog in 2015.

Collection of weather data

• Hourly weather data are needed to run model for advisory• Currently using weather stations at a limited number of locations• Considering a weather data service ($100-$200 per site per year)

2014 Conclusions• Fungicide applications are more likely to result in a

significant yield response if favorable conditions for disease development occur within 7 days of the R3 stage.

• Fungicide applications made when weather conditions are favorable for disease development are likely to be profitable.

• Additional years of data including ranges of environmental conditions and detailed assessments of crop and disease development are needed.

2015 Objectives

1. Validate and optimize a weather-based disease advisory for foliar fungicide application in soybean

2. Survey soybean fields for fungicide resistant pathogens

Objective 1: Validate and optimize weather-based disease advisory

• Collect second year of data to validate and optimize weather-based parameters for timing fungicide applications

• Repeat small-plot and on-farm trials comparing growth stage and weather-based fungicide applications

• Collect more detailed information on disease and crop development over time

Objective 2: Survey soybean fields for fungicide resistant pathogens

• Control/management• Resistant cultivars (best)• Rotate out of soybean• Foliar fungicides

• Generally not a problem in VA

• High severity in some fields in 2013 & 2014 (defoliation)

• Potential for up to 30% yield loss in some fields

Frogeye leaf spot (FLS)Causal agent = Cercospora sojina

Virginia - fungicide resistant isolates of FLS confirmed in 2 out of 4 fields sampled in 2014

Strobilurin resistant frogeye leaf spot

Fungicide Resistance

Quinone outside inhibitors (QoIs)/strobilurins are highly effective, broad-spectrum fungicides BUT fungicide resistance can occur rapidly within pathogen populations leading to disease control failures

• Inhibit mitochondrial respiration of fungi by binding to cytochrome bc1 enzyme complex at Qo site (site specific mode of action)

• G193A mutation: Glycine Alanine at codon 143 (complete resistance)

• Single base change in DNA sequence: GGT GCT

Sensitive

Resistant

DNA sequence from cytochrome b gene in Cercospora sojina (frogeye leaf spot fungus)

Strobilurin / QoI fungicides

A DNA-based assay can be used to identify strobilurin resistant FLS

Fungal isolate or infected plant tissue

Extract DNA Amplify DNA by PCR (target sequence conferring sensitivity / resistance to strobilurin fungicides)

Visualize DNA (PCR product) on agarose gel

Resistance mutation

Wild-type (sensitive)

Determine frequency and distribution of strobilurin resistant FLS in Virginia

Why Monitor Resistance?

• Resistance control failures crop losses

• Use of ineffective fungicides may increase resistant strains of fungi

Fungicide trade name

Fungicide common name

Fungicide class* Production rate per acre

Quilt Xcel azoxystrobin + propiconazole

strobilurin + triazole 14.0‑21.0 fl oz

 

Quadris TOP azoxystrobin + difenoconazole

strobilurin + triazole 8.0‑14.0 fl oz

 

Stratego YLD trifloxystrobin + prothioconazole

strobilurin + triazole 4.0-4.65 fl oz

 

Priaxor pyraclostrobin + fluxapyroxad

strobilurin + carboxamide

4.0-8.0 fl oz

 

Aproach Prima picoxystrobin

cyproconazole

strobilurin + triazole 5.0-6.8 fl oz

Pre-mix fungicides are recommended for fungicide resistance management. However, if strobilurin resistance becomes widespread in Virginia, different fungicide modes of action or rates may need to be recommended.

Fungicides Pre-mixes for Resistance Management

2015 Budget RequestItem Amount requested Graduate student (100%) Salary $ 22,021

Fringe benefits $ 1,486

Wage employee Salary (2 months) $ 4,000

Fringe benefits $ 310

Materials/supplies $ 2,000

TOTAL $ 29,817

Questions?