Persistence of fungicide efficacyon mandarin fruit – a case study in

the future of chemical control?Andrew Miles (R&DPI Pty Ltd)Dan Papacek (Bugs for Bugs)

A necessary evil?

• “Factors driving the markets for fungicides include decreasing arable land, increasing population and the requirement of improving crop yields”…

• “Global consumption of synthetic fungicides is projected to reach 659.25 thousand tons by volume and US$14.8 billion by value by 2020”…

• “regulatory authorities such as EPA (Environment Protection Agency) frequently come up with stringent laws related to curbing pesticide use for alleviating, environmental damage and increasing consumer awareness about pesticide consumption”…

Research and Markets; Global Fungicide market - Growth,Trends, Forecast for the period 2015-2020Biotech Business Week (Jun 29, 2015): 357.

A greater good?

• Discerning markets (EU) want low/very low agrichemical residues in food

• Industries are rising to the challenge:• KiwiGreen – New Zealand• NZ Apple Futures – New Zealand• Residue 0 for citrus – Spain

• Using disease forecasting, residue decline modelling, IPM etc to reach targets such as:

Maximum Residue Levels (MRLs) at below 10% of the EU MRL, with 3 or less active ingredients allowed per residue test

• Growers getting a return through maintaining market access.

Cunningham, N., Leo, N. & Taverner, P. (2015).Chemical usage in Australian Citrus: Situational Analysis. South Australian Research and Development Institute.

What does this mean for chemical control research?

Existing requirements:

• Efficacy

• Crop/economic compatibility

• Resistance management

Emerging requirements:

• Export market residue acceptance

• Residue decline characteristics

• Flexible use patterns

• Optimised applications

• Needs a thorough understanding of the chemical and the target

Mandarin production in Queensland…

•~3,500 ha•~85 orchards•~12% of AUS citrus•~50% of AUS mandarins•Murcott and Imperial•Fresh domestic and export

http://www.oranges.com.au/industry/

Mandarin production in Queensland…

•Subtropical / tropical region is well suited to mandarins, but…

http://www.oranges.com.au/industry/

Two major pathogens with very different disease cycles…

Citrus black spotPhyllosticta citricarpa

‘Emperor’ brown spotAlternaria alternata

Two major pathogens with very different disease cycles…

Citrus black spotPhyllosticta citricarpa

‘Emperor’ brown spotAlternaria alternata

Fruit at risk for the first 20-24 weeks Fruit at risk at all times (~40 weeks)!

Intervention is needed!$7M applying fungicides:

• Copper

• Mancozeb (dithiocarbamate)

• Azoxystrobin (strobilurin)

• Iprodione (dicarboximide)

But still $8-12M lost to downgraded fruit…why?

• Current labels at best offer ~23 weeks of protection during a 40-week season

• Some use patterns are outdated for current cultivars and diseases

• Restrictive MRLs in some cases

Additional fungicide options are required

…along with other management strategies…

All available fungicides

~20 possibilities

11 worth field testing

Efficacy testing summary• 11 fungicides

• 6 trials

• 3 seasons

• 2 diseases (black spot, brown spot)

• 5 cultivars (Imperial, Murcott, Daisy,

Blood orange, IrM2)

High performing fungicides:

• Captan (phthalimide)

• Boscalid or fluxapyroxad (SDHI)

• Dithianon (quinone)

Export MRLs (mg/kg):

Country Captan Dithianon Boscalid

Thailand - Codex (2)Hong Kong Codex (2)

Taiwan *0.01 4 -

China 5 -Japan 5 10 10

Singapore 15 Codex (2)Russia - -

Malaysia Codex (2)Netherlands 0.02 2

Note: fluxapyroxad is too new to have any MRLs in citrus

Efficacy is determined, need to know the efficacy duration• Re-application intervals

• Cost benefit

• Appraisal of existing use patterns

• Implications for resistance management

Perform an efficacy persistence experiment using Alternaria alternata as a bioassay

• Reliable sporulation in culture

• Rapid symptom development

Methods – field trial establishment• Based largely on Vicent, A., Armengol, J. & Garcia-Jimenez, J. (2007). Rain

Fastness and Persistence of Fungicides for Control of Alternaria Brown Spot of Citrus. Plant Disease 91(4): 393-399.

• Apply a single application of each fungicide when fruit ~45mm (February)

• 4 replicate trees each, hand sprayed

• 4 untreated trees

• Randomised design

Existing: Promising candidates:Mancozeb BoscalidIprodione FluxapyroxadAzoxystrobin Captan

Dithianon

Methods – Alternaria alternata bioassay• Sample 10 fruit per tree at 1, 11, 21, 33 & 64 days

• At each sampling time:

• Fruit sampled onto HDPE mounting boards

• Each fruit inoculated in four positions with 5mm

diameter blotting paper discs soaked in 1×105

conidia/mL

• Add water to bottom of plastic containers and seal

• Incubate @ 24˚C for 72 hours

• Assess the number of lesions developing under

each disc:

• 0 = no lesions; 1 = 1 to 5 lesions; 2 = >5 lesions

Results• Mean rating of the four inoculation points expressed as % disease control relative

to the untreated fruit.

• Data analysed by ANOVA

Results: existing fungicides

Results: existing fungicides

Results: existing fungicides

Results: new multisite fungicides

Results: new multisite fungicides

Results: new multisite fungicides

Results: SDHI fungicides

Results: SDHI fungicides

Results: SDHI fungicides

Results summary:• Largest difference in efficacy between fungicides is within the first 11 days

• Efficacy reduces by ~50% in the first 11 days

• From 21 days onwards efficacy of all fungicides is greatly reduced

• Iprodione and captan significantly higher disease control at 1 and 11 days

• Of the two SDHI fungicides: fluxapyroxad > boscalid

• Efficacy in the bioassay may be an indicator of inhibition of germination

Conclusions• Arbitrary application intervals of 4-5 weeks are unlikely to be an effective

approach – tighter intervals targeting infection periods would be preferable

• Promising new fungicides, particularly captan, should return on investment

• Experiment needs to be repeated this season

Consequences• Some promising options, but is there a future in fungicide dependence?

• Fungicide applications are only highly effective for short periods of time

• Can’t just spray more often - need less residues, not more

• A major infection event outside the time high efficacy will be damaging

Beyond fungicides…Host resistance

• Inoculation of hybrid seedlings and disposal of susceptible hybrids• >30,000 A. alternata resistant hybrids for horticultural evaluation

Pathogen biology and disease epidemiology

• CT13021 - Joint Florida and Australia citrus black spot research initiative• QAAFI project• Searching for sources of resistance to black spot• Understanding the patterns of sporulation• Determining the timing of infection in orchards

Biological control

• Needs more attention

Can we meet the future demands on chemical control?• Export market pressures are creating an incentive that has been missing

Residues are likely to be the new technical barriers trade

• Addressing gaps in knowledge of pathogen biology and

disease epidemiology is growing in importance

• As registration requirements get stricter (slower), biological

control and “long term” strategies such as resistance

breeding look more appealing

Thank you to the people that makes things happen!

• Dan Papacek & team at Bugs for Bugs

• Mal Wallis & team at CitriCare

• Andre Drenth, Tim Shuey, Nga Tran @ UQ

• Malcolm Smith & DAF team at Bundaberg

• Greg Parr, Craig Wallis, Mark Trott, Gavin Ford, Carl Robinson, Michael McMahon, Ben Barclay

• Kevin Bodnaruk, Dale Griffin, Andrew Harty

This research was funded by Horticulture Innovation Australia using the citrus industry levy and matched funds from the Australian Government.