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 omafra sherf •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 wikia •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 3233°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 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 sitespecific materials can provide syngergistic control (and good resistance management) •Use chlorothalonil judiciously, <6 applications/season (6-10 applications of chlorothalonil can suppress yields) 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 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 Badge SC mancozeb M3 chlorothalonil M5 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-Count-N copper hydroxide M1 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, TMethyl E-AG 4.5F, Incognito 4.5F, Onset Iprodione 4L Ag Fungicide, Rovral 4 Flowable Fungicide, Nevado 4F thiophanate-methyl 1 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: [email protected]
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