Validation Optimization and Deployment of Fungicide Advisories for

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

Growth stage-based fungicide applications Fungicide Spray Window

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

Soybean Weather-Based Fungicide Advisory: Validation Trials 2014 Treatments R 3 Fungicide Advisory Fungicide * * No Fungicide Eastern Virginia AREC (Warsaw) * * 7 on-farm trials 2 small plot studies (ARECs) Weather station * Tidewater AREC (Suffolk) *

130 TAREC 120 11. 6 bu/A R 3 2. 7 bu/A 0. 2 bu/A 100 Single application Advisory 1 1 week spray* after R 3 Each % yield response = 0. 6 bu/A 2 weeks after R 3 3 weeks after R 3 7. 0 bu/A 110 Multiple applications EVAREC 5. 3 bu/A 5. 1 bu/A % yield response compared to untreated Fungicide timing vs yield response *Weather advisory and growth stagebased sprays were made on the same date 4 weeks R 3 & 21 Advisory 2 Weekly after R 3 days after sprays* sprays R 3 between R 3 and R 5 Fungicide application timing TAREC (Suffolk) – Cercospora blight EVAREC (Warsaw) – Frogeye leaf spot

County Orange Variety Asgrow AG 4633 Treatment Control R 3 Spray Date NA July 29 Decision Aid Aug 4 Priaxor - 4 oz/A 52. 0 A Culpeper NK S 41 -J 6 Control R 3 NA Aug 11 Priaxor – 4 oz/A 61. 0 A 59. 7 A Stafford Pioneer P 39 T 67 Decision Aid Control R 3 Aug 20 NA Aug 7 Priaxor – 4 oz/A Quadris Top - 11 oz/A 57. 2 A 67. 8 A 69. 7 A Amelia Armor 5363 Decision Aid Control Aug 16 NA Quadris Top - 11 oz/A 70. 2 A 41. 4 C R 3 Aug 15 Quadris Top – 10 oz/A 47. 7 A Nottoway Decision Aid Control Aug 20 NA Quadris Top – 10 oz/A 46. 1 B 45. 4 B R 3 Sept 16 46. 7 A Sussex Hubner H 53 -12 R 2 Decision Aid Control Sept 26 NA 46. 7 A 30. 0 B R 3 Stratego YLD – 6 oz/A 34. 2 A Decision Aid Sept 3 Sept 16 (Sept 9) Stratego YLD – 6 oz/A 32. 7 A Accomack Channel 4206 Control NA 54. 7 A & 4306 R 3 Sept 11 Stratego YLD – 4 oz/A 53. 6 A Decision Aid Sept 15 Stratego YLD – 4 oz/A 48. 8 A Fungicide & Rate Priaxor - 4 oz/A Yield (bu/A) 47. 4 B 52. 6 A

Yield (% of untreated control) “Favorable days” vs yield response 120 +4 -6 bu/A R 3 Decision Aid 110 100 +1 -2 bu/A R 2 = 0. 9421 R 2 = 0. 9783 90 4 6 8 10 12 #of days between R 3 growth stage and favorable days for disease 14

Yield response needed to offset cost of fungicide application in soybean Soybean price/bu Treatment cost/A $9 $10 $11 $12 $13 $14 $15. 00 1. 7 1. 5 1. 4 1. 3 1. 2 1. 1 $17. 50 $20. 00 $22. 50 $25. 00 $27. 50 $30. 00 $32. 50 $35. 00 1. 9 2. 2 2. 5 2. 8 3. 1 3. 3 3. 6 3. 9 1. 8 2. 0 2. 3 2. 5 2. 8 3. 0 3. 3 3. 5 1. 6 1. 8 2. 0 2. 3 2. 5 2. 7 3. 0 3. 2 1. 5 1. 7 1. 9 2. 1 2. 3 2. 5 2. 7 2. 9 1. 3 1. 5 1. 7 1. 9 2. 1 2. 3 2. 5 2. 7 1. 3 1. 4 1. 6 1. 8 2. 0 2. 1 2. 3 2. 5 Favorable days for disease development: < 8 days after R 3 4 -6 bu/A yield response > 8 days after R 3 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 R 3 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

Strobilurin resistant frogeye leaf spot Virginia - fungicide resistant isolates of FLS confirmed in 2 out of 4 fields sampled in 2014

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

Strobilurin / Qo. I fungicides • Inhibit mitochondrial respiration of fungi by binding to cytochrome bc 1 enzyme complex at Qo site (site specific mode of action) • G 193 A 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)

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 Determine frequency and distribution of strobilurin resistant FLS in Virginia Resistance Wild-type mutation (sensitive)

Why Monitor Resistance? • Resistance control failures crop losses • Use of ineffective fungicides may increase resistant strains of fungi

Fungicides Pre-mixes for Resistance Management Fungicide trade name Fungicide common name Fungicide class* Production rate per acre Quilt Xcel azoxystrobin + propiconazole strobilurin + triazole 14. 0‑ 21. 0 fl oz azoxystrobin + difenoconazole strobilurin + triazole trifloxystrobin + prothioconazole strobilurin + triazole pyraclostrobin + fluxapyroxad strobilurin + carboxamide 4. 0 -8. 0 fl oz picoxystrobin strobilurin + triazole 5. 0 -6. 8 fl oz Quadris TOP Stratego YLD Priaxor Aproach Prima 8. 0‑ 14. 0 fl oz 4. 0 -4. 65 fl oz cyproconazole 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.

2015 Budget Request Item Graduate student (100%) Salary Fringe benefits Wage employee Salary (2 months) Fringe benefits Materials/supplies TOTAL Amount requested $ 22, 021 $ 1, 486 $ 4, 000 $ 310 $ 2, 000 $ 29, 817

Questions?