Regionally RelevantFungicide Programs

for Common Onion Pathogensin the Columbia Basin

Pacific Northwest Vegetable AssociationAnnual Convention & Trade Show

14-15 November 2018, Kennewick, WA

Lindsey du ToitWashington State University

Application of a pesticide to a crop or site that is not on the label is a violation of pesticide law and may

subject the applicator to civil penalties.

In addition, such an application may also result in illegal residues that could subject the crop to seizure

or embargo action.

It is your responsibility to check the label before using any product to ensure lawful use, and obtain

all necessary permits in advance.

Types of plant pathogens- Fungi- Oomycetes- Bacteria- Phytoplasmas- Viruses- Viroids- Nematodes

From Agrios

Stemphyliumleaf blight True fungus

Downy mildew

Oomycete = water mold

Bacterial leaf blight

Bacterium

• Types of products:Fungicide, oomyceticide, bactericide, nematicide, …

• Modes of action, broad vs. narrow spectrum• Contact vs. systemic• Protectant vs. curative• Efficacy also affected by:

• Timing of application, coverage, rate• Management of resistance:

Fungicide Resistance Action Committee (FRAC) Groups – high risk groups, rotate groups, don’t use reduced rates of application

Effective use of fungicides

https://pnwhandbooks.org/plantdisease/pesticide-articles

“Systemic” fungicides

translaminar

locally systemicsystemic

Apoplastic = xylem = UP the plant (e.g., Ridomil, FRAC Grp 4)Symplastic = phloem = UP & DOWN (e.g., Aliette, FRAC Grp 33)

https://pnwhandbooks.org/plantdisease/pesticide-articles

Case Study 1: Application of Fontelis (penthiopyrad = FRAC Group 7) for control of pink root of onion

Where to apply?

When to apply?

How to apply?

What to apply?

Case Study 2: Neck rot

Botrytis species on Allium cropsB. aclada B. allii B. byssoidea B. cinerea

B. porri B. squamosa B. tulipae B. elliptica

Neck rot vs. Botrytis leaf

blight(Botrytis squamosa)We do NOT see this in the

Columbia Basin

APS Press

In vitro efficacy of fungicides against B. aclada6 days after plating on fungicide-amended agar

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Infection of onion plants by neck rot fungi

• Weak, opportunistic pathogens• Only latent infections of healthy tissue• Active, sporulating infections require:

1. Dead/injured host tissue• natural senescence, e.g., ‘tops down’• injured: transplanting, hail, cultivation

2. Moisture• rain, irrigation, dew• moisture in/on senescing tissue

• Cool to warm temperatures (60-80oF)• Excessive N fertility, irrigation

When to apply fungicides for neck rot fungi in onion bulb crops in the Columbia Basin

• Periods of natural senescence:• tops down = 3-4 weeks before harvest• moisture in necks + senescence = high risk• ‘bull necks’ = high risk• cool or moist field curing conditions = high risk

• Immediately after injury:• transplanting, ‘cultivator blight’, hail, …

• Fungicide spray program:• 10-14 day interval during vulnerable period• good coverage• mix or alternate fungicide modes of action

When to apply fungicides for Botrytisin onion seed crops?

• Natural senescence:• spring: leaves senesce at base of scape• late spring: spathe (membrane) around umbels

• Injury: • ‘cultivation blight’, hail, …

• Fungicide spray program:• 1x or 2x (7-14 day interval)• At start of senescence or immediately after injury• Adequate volume water for coverage• Mix or alternate fungicide modes of action

Case Study 3:

Downy mildew & Stemphylium leaf blight

Opportunistic infection: Stemphylium vesicarium

M. Trent

Stemphylium vesicarium &

thrips damage (also

with IYSV)

Stemphylium vesicarium & downy mildew on onion scapes

13 August 2014

2014 Downy Mildew Outbreak in NY

27 August 2014

Christy Hoepting, Cornell Extension

A. Initial, preventative program:

• Mancozeb or phosphorous acid– Tank mix when fungicides have no DM activity

• E.g., Luna Tranquility, Inspire Super, Scala, Rovral

– Mancozeb better than phosphorous acid

• FRAC Group 11 fungicides– Quadris Top (3, 11)

– Merivon (7, 11)

– Tanos (11, 27)

Cornell University recommendedfungicide program for DM & SLB

C. Hoepting, Onion World Sep/Oct. 2016

Cornell University recommendedfungicide program for DM & SLB

Product (rate per acre)FRACgroups

Disease(s)controlled

Weeks 1, 2 & 4

Ridomil Gold Bravo 2.5 pt*+ mancozeb 3 lb+ Luna Tranquility 16 fl oz

4, M5M37, 9

DMDMSLB

Weeks 3, 5:

Orondis 1.6 fl oz+ Quadris Top

US153, 11

DMSLB, DM

* No more than 2 consecutive applications of Ridomil Gold Bravo (maximum 3 applications)

B. Once DM is detected:

C. Hoepting, Onion World Sep/Oct. 2016

Temperature & moisture effects in central WA

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Months of a biennial onion seed crop in central WA

Mean t

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ture

(F

)Direct-seeding Bulb planting Harvest

Thrips (IYSV), bacteria

Fungi/oomycetes (Botrytis, downy mildew)

2016

Downy mildew & Stemphylium leaf blight

• “Typical” weather• “Typical” diseases• Scouting, accurate diagnoses• Fungicide program:

• timely applications• efficacious product(s)• crop coverage (aerial vs. chemigated vs. sprayboom)• 10-14 day interval only during vulnerable period• mix or alternate FRAC groups• no need for “Cadillac” NY fungicide program in the semi-arid Columbia Basin, even under center pivots

Case Study 4:

Onion bacterial diseases

• There are no systemic bactericides• Coppers are the most effective bactericides• Coppers are purely protectant

Effect of timing of ManKocide application on bacterial blight

du Toit & Derie (2008) PDMR 2:V008

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No ManKocide

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Effect of Tanos (famoxadone + cymoxanil, FRACGroups 11 + 27) on copper hydroxide

du Toit & Derie (2008) PDMR 2:V009

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Non-inoculated control

Inoculated control

Tanos

Kocide 3000

Kocide + Tanos

ManKocide DF

ManKocide + Tanos

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• Part of integrated disease management programs• Monitor/scout:

• Appearance/development• Threshold populations• Need for control• Effectiveness of actions taken

• Cultural practices• Resistant or tolerant cultivars, if available• KNOW THE ENEMIES: Who, When, How• UNDERSTAND THE TOOLS: What, How, When

Regionally relevant fungicide programs

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