Originally presented at the WPVGA Ed

Conference Feb 2, 2011

Stevens Point, WI – 11:15-11:45AM

-content updated July 12, 2012

Amanda Gevens

Extension Plant Pathologist

University of Wisconsin-Madison

Fungicide Updates in Onion

Common Onion Diseases in WI

Botrytis Neck Rot

Botrytis allii Botrytis Leaf Blight

Botrytis squamosa Purple Blotch

Alternaria porri Downy Mildew

Peronospora destructor Bacterial Rots

Pseudomonas and

Pectobacterium spp.

Botrytis Neck Rot

•Common disease in stored onions with previous injury

•Favored by cool, wet conditions and poor drying and curing of onions

•Infected bulbs rot in storage

•Fungicides are generally ineffective for neck rot control

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Botrytis Leaf Blight

•Widespread fungal disease of onion

•Favored by warm, humid weather – mid to late season

•Causes blighting and early death of leaves, undersized bulbs, low yield

•Fungicides can control Botrytis leaf blight

Purple Blotch

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•Common in many US onion-growing regions – overwinters in residue

•Promoted by long periods of rain or heavy dew

•Often seen with other fungal diseases

•Fungicides can control Purple blotch

Downy Mildew

•Serious yet sporadic disease

•Driven by cool, moist conditions

•Causes blighting and early death of leaves, undersized bulbs, low

yield, poor storability

•Fungicides can control Downy mildew

Bacterial Rots

•Widespread and destructive storage disease of onions

•Initiated right before or at harvest of bulbs

•Bacteria reside in soil and plant debris – maggots can spread disease

•Infection typically occurs after plant becomes wounded (hail damage)

or leaves senesce

•Disease favored by warm and wet conditions

•Copper-containing fungicides applied quickly after rain/hail event can

aid in curing of wounds and limit bacterial infection

Bacterial Rots

•Management options include cultural and chemical methods

•Minimize injury to maturing and harvested bulbs

•Harvest bulbs after necks are appropriately dried

•Dry onions thoroughly before storage, and store at temp of 32-

33°F and at >70%RH with good ventilation

•Avoid highly susceptible varieties such as Spanish sweet

types - there are no resistant varieties

•Control insects such as maggots

•Copper-containing fungicides applied quickly after rain/hail

event can aid in curing of wounds and limit bacterial infection

•Copper-containing fungicides are ineffective if applied after

symptoms develop

Best Cultural Management Practices

For Onion Diseases in WI

•Plant disease-free seedlings or sets

•Do not plant >0.25 inch below soil surface

•Rotate crops (out of Alliaceae family) for 2-3 years

•Scout regularly for early signs of pest/disorder

•Destroy volunteers or cull onions to reduce pathogen

•Field sanitation – remove onion debris

•Avoid late season N application

•Avoid harvest injuries, harvest mature bulbs with a few

inches of neck remaining, and harvest in dry weather

•Proper drying conditions prior to storage (~90°F for >5 days)

•When fungicides are needed, apply effective

materials, providing good coverage, at appropriate

times

•Excessive rainfall promotes many diseases and

interferes with timing and persistence of fungicides

•With currently >50 fungicides registered for use on

onions in WI, selection of appropriate materials can

be confusing

Onion Fungicides

•Start of fungicide program can vary depending upon the weather

– but by mid-June environmental conditions may favor disease and

preventative programs should start

•Disease forecast tool may dictate start, or threshold of lesions

(such as average of 1 Botrytis leaf blight lesion/plant/field)

•Use of broad spectrum protectants such as chlorothalonil

(Botrytis & Purple blotch) and mancozeb (Downy mildew) are good

first choices

•Control of some diseases can be further enhanced by alternating

broad spectrum materials with site-specifics such as: strobilurins,

triazoles, and other classes

•Tank-mixing mancozeb and/or chlorothalonil with site-

specific materials can provide syngergistic control (and good

resistance management)

•Use chlorothalonil judiciously, <6 applications/season (6-10

applications of chlorothalonil can suppress yields)

Onion Fungicides

Fungicide trade name

Fungicide active

ingredient

Botrytis leaf blight

Purple blotch Downy mildew

Bacterial rots

Bravo, Echo, Equus, Initiate

chlorothalonil Good Good Modest -

Dithane, Manzate, Penncozeb

mancozeb Good Good Excellent -

Kocide, Champ Formula II, Champion

coppers Modest Modest Modest Good

Quadris, Cabrio, Reason, Pristine

azoxystrobin, pyraclostrobin, fenamidone, pyraclostrobin + boscalid

Excellent Excellent Excellent -

Ridomil mefenoxam - - Excellent -

Scala pyrimethanil Excellent Excellent - -

Rovral, Iprodione iprodione Excellent Excellent Good -

Switch cyprodinil + fludioxonil

Excellent Excellent Excellent -

Omega fluazinam Excellent Excellent Modest -

Forum dimethomorph - - Excellent -

Aliette fosetyl-al - - Excellent -

Comments on the Performance of Other or

Newly Registered Onion Fungicides

Very effective at controlling downy

mildew: Quadris Top

(azoxystrobin+difenoconazole), Inspire

Super (cyprodinil+difenoconazole), Revus

(mandipropamid)

Effective at controlling purple blotch:

Folicur (& other trade names), Endura

(also effective on Botrytis leaf blight)

Varied disease control performance with:

Tanos and Ranman

Fungicide Active ingredient Fungicide Resistance Action

Committee code (FRAC)

Dithane DF Rainshield, Dithane F45

Rainshield, Dithane M45, Manzate, Manzate

Pro-Stick Fungicide, Penncozeb 4FL, 75DF,

80WP

mancozeb M3

Bravo Zn, Echo Zn, Bravo WeatherStik,

Bravo Ultrex, Chloronil 720, Echo 720, Echo

90DF, Chlorothalonil 720SC, Equus 500 Zn,

Initiate Zn, Equus 720 SST, Initiate 720,

Equus DF

chlorothalonil M5

Badge SC copper hydroxide + copper oxychloride M1

C-O-C-S WDG copper oxychloride sulfate M1

Champ DP Dry Prill, Champ WG, Champ

Formula 2 Flowable, Champion WP, Kocide

2000, Kocide 3000, Kocide DF, Kentan DF,

Nu-Cop 3L, Nu-Cop 50DF

copper hydroxide M1

Copper-Count-N copper ammonium complex M1

Cueva copper octanoate M1

Cuprofix Ultra 40 Disperss basic copper sulfate M1

Nordox, Nordox 75WG cuprous oxide M1

Cuprofix MZ Disperss basic copper sulfate + mancozeb M1 + M3

Mankocide copper hydroxide + mancozeb M1 + M3

Fungicide Active ingredient Fungicide Resistance Action

Committee code (FRAC)

MicroSulf, Microfine sulfur, Microthiol

Disperss, Kumulus DF, Super-Six

sulfur M2

Thiophanate Methyl 85-WDG, Topsin 4.5FL,

Topsin M 70WDG, Topsin M 70WP, Topsin M

WSB, Topsin 4.5FL, T-Methyl 70W WSB, T-

Methyl E-AG 4.5F, Incognito 4.5F, Onset

thiophanate-methyl 1

Iprodione 4L Ag Fungicide, Rovral 4

Flowable Fungicide, Nevado 4F

iprodione 2

Folicur 3.6F, Tebuzol 3.6F, Toledo,

Monsoon, Orius 3.6F, Tebustar 3.6L

tebuconazole 3

Propiconazole E-AG 41.8 EC, Propimax EC,

Tilt, Bumper 41.8EC, Topaz

propiconazole 3

Metastar 2E AG, Allegiance, Sebring 2.65ST metalaxyl 4

Ridomil Gold EC, Ridomil Gold SL, Ultra

Flourish, Apron XL

mefenoxam 4

Endura boscalid 7

Fontelis penthiopyrad 7

Scala SC pyrimethanil 9

Vangard WG cyprodinil 9

Cabrio EG pyraclostrobin 11

Dynasty, Heritage, Quadris azoxystrobin 11

Reason 500SC fenamidone 11

Fungicide Active ingredient Fungicide Resistance Action

Committee code (FRAC)

Maxim 4FS fludioxonil 12

Botran 75W DCNA Dichloran 14

Actigard 50WG acibenzolar s-methyl 21

Omega 500f fluazinam 29

Aliette, Lesion 80 WDG, Linebacker WDG fosetyl-al 33

Phostrol phosphorous acids 33

Fosphite, FungiPhite, ProPhyt, Alude,

Rampart

potassium phosphite 33

Phorcephite potassium phosphate, potassium phosphite 33

Forum dimethomorph 40

Revus mandipropamid 40

Quadris Top azoxystrobin + difenoconazole 11 + 3

Quilt Excel azoxystrobin + propiconazole 11 + 3

Fungicide Active ingredient Fungicide Resistance Action

Committee code (FRAC)

Quadris Opti axoxystrobin + chlorothalonil 11 + M5

Tanos cymoxanil + famoxadone 27 + 11

Ridomil Gold Copper mefenoxam + copper hydroxide 4 + M1

Ridomil Gold MZ WG mefenoxam + mancozeb 4 + M3

Ridomil Gold Bravo SC chlorothalonil + mefenoxam 4 + M5

Quadris Opti axoxystrobin + chlorothalonil 11 + M5

Pristine boscalid + pyraclostrobin 7 + 11

Switch 62.5WG cyprodinil + fludioxonil 9 + 12

Inspire Super cyprodinil + difenoconazole 9 + 3

Serenade ASO, Serenade MAX, Cease Bacillus subtilis strain QST 713 bio

Actinovate AG Streptomyces lydicus WYEC 108 bio

Contans WG Coniothyrium minitans strain CON/M/91-08 bio

Regalia Reynoutria sachalinensis Group P bio

Fungicide Active ingredient Fungicide Resistance Action

Committee code (FRAC)

Rhapsody Bacillus subtilis strain QST 713 bio

SoilGard 12G Gliocladium virens Gl-21 bio

Sonata Bacillus pumilis strain QST 2808 bio

Kaligreen potassium bicarbonate NC

Trilogy neem oil NC

Oxidate hydrogen dioxide NC

Rhapsody Bacillus subtilis strain QST 713 bio

SoilGard 12G Gliocladium virens Gl-21 bio

Sonata Bacillus pumilis strain QST 2808 bio

Kaligreen potassium bicarbonate NC

Trilogy neem oil NC

Rotate between fungicide classes (FRAC #) to

manage risk of resistance

Thank you!

Acknowledgements/References PDMN reports - Dr. Mary Hausbeck, MSU

Efficacy reports – Dr. Beth Gugino, PSU

Disease publications – Dr. James Lorbeer, Cornell

Disease publications – Dr. Walt Stevenson, UW

Amanda J. Gevens

Assistant Professor & Extension Plant Pathologist

1630 Linden Dr. Rm. 689

Plant Pathology

University of Wisconsin

Madison, WI 53706

Email: gevens@wisc.edu