Fungicide Updates in Onion - Department of Plant Pathology

Fungicide Updates in Onion 

Amanda Gevens 

Extension Plant Pathologist 

University of Wisconsin-Madison 

Originally presented at the WPVGA Ed 

Conference Feb 2, 2011 

Stevens Point, WI – 11:15-11:45AM 

-content updated July 12, 2012

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 

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•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

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


•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


•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)

Onion Fungicides 

•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

•Use chlorothalonil judiciously,

Fungicide 

trade name 

Bravo, Echo, 

Equus, Initiate 

Dithane, 

Manzate, 

Penncozeb 

Kocide, Champ 

Formula II, 

Champion 

Quadris, Cabrio, 

Reason, Pristine 

Fungicide 

active 

ingredient 

Botrytis leaf 

blight 

Purple blotch 

Downy 

mildew 

Bacterial rots 

chlorothalonil Good Good Modest - 

mancozeb Good Good Excellent - 

coppers Modest Modest Modest Good 

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 

mancozeb 

M3 

Rainshield, Dithane M45, Manzate, Manzate 

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

80WP 

Bravo Zn, Echo Zn, Bravo WeatherStik, chlorothalonil 

M5 

Bravo Ultrex, Chloronil 720, Echo 720, Echo 

90DF, Chlorothalonil 720SC, Equus 500 Zn, 

Initiate Zn, Equus 720 SST, Initiate 720, 

Equus DF 

Badge SC copper hydroxide + copper oxychloride M1 

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

Champ DP Dry Prill, Champ WG, Champ copper hydroxide 

M1 

Formula 2 Flowable, Champion WP, Kocide 

2000, Kocide 3000, Kocide DF, Kentan DF, 

Nu-Cop 3L, Nu-Cop 50DF 

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



MicroSulf, Microfine sulfur, Microthiol 

Disperss, Kumulus DF, Super-Six 

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 

Iprodione 4L Ag Fungicide, Rovral 4 

Flowable Fungicide, Nevado 4F 

Folicur 3.6F, Tebuzol 3.6F, Toledo, 

Monsoon, Orius 3.6F, Tebustar 3.6L 

Propiconazole E-AG 41.8 EC, Propimax EC, 

Tilt, Bumper 41.8EC, Topaz 

sulfur 

thiophanate-methyl 1 

iprodione 2 

tebuconazole 3 

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 

M2 

Fontelis penthiopyrad 7 

Scala SC pyrimethanil 9 

Vangard WG cyprodinil 9 

Cabrio EG pyraclostrobin 11 

Dynasty, Heritage, Quadris azoxystrobin 11 

Reason 500SC fenamidone 11



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



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



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

Fungicide Updates in Onion - Department of Plant Pathology

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