Efficacy of Fungicides for Early and Late Blight Control in Tomato Thomas A. Zitter Jessica L. Drennan Department of Plant Pathology Cornell University Ithaca, NY 14853 Early Blight symptoms Alternaria tomatophila – light phenotype Early blight (EB) is an important disease of tomato Few varieties exist with resistance/tolerance to EB The Early Blight fungus is now known to exist as two different species: • Alternaria solani – traditional Early blight of potato Infects tomato but much less so • Alternaria tomatophila – Early blight of tomato with two phenotypes Dark Phenotype and Light Phenotype differ in culture but not morphologically Light Phenotype is significantly more pathogenic on tomato Fungicides are required for control for current commercial varieties Field Trials (10 years) Same • Field: No rotation • Variety: Supersonic, Fresh Market, ID • Spreader rows (EB) • Weekly fungicide applications (7-9x) • Rating: Horsfall-Barratt Scale (0-11) • Timeframe the same Different • Weather conditions • Inoculum Supersonic – EB susceptible Late Blight Phytophthora infestans An oomycete that infects both potato and tomato The isolate used, US17, usually only infects tomato and is less virulent than other isolates Isolate US17 inoculated three times on tomato plot: August 17, 24, 28 Variety Supersonic – usually foliar symptoms and/or susceptible to fruit infection Forget the Galoshes! Break Out the Hip waders! New York in 2006 – A very wet summer The rainiest summer ever recorded in Tompkins Co., NY May – 2.72” June – 7.77” July – 7.54” August – 5.02” September – 2.49” Sections of our field were regularly in standing water Plants in the mildest depressions in the field suffered from poor root systems - WET FEET SYNDROME Supersonic – Late Blight Susceptible – US-17 Supersonic - Older plant Another variety – Younger plant 2004 – Br Quadris Opti 2006 – Br Quadris Opti 3.2 T216/M201/EB16 T118/M101/EB17/LB0 2004 – Dithane/Endura/Forum 2006 – Dithane/Endura/Forum 3.8 T224/M220/EB2 T99/M74/EB10/LB14 Fungicides Tested, 2006 1. Control 2. Bravo Ultrex, 1.8 lb (8x) 3. Dithane Rainshield, 2.0 lb (8x) 4. Bravo Ultrex (5x); Ranman, 2.75 fl oz + Silwet, 2.0 fl oz (3x) 5. Bravo Ultrex (5x); Ranman, 2.10 fl oz + Silwet, 2.0 fl oz (3x) 6. Bravo Ultrex (5x); Ranman, 2.10 fl oz + Silwet, 2.0 fl oz + Dithane, 2.0 lb (3x) 7. Bravo Ultrex (5x); Ranman, 2.75 fl oz + NIS, 0.25 v/v + Dithane, 2.0 lb (3x) 8. Bravo Ultrex (5x); Ranman, 2.75 fl oz (3x) + Dithane, 2.0 lb (3x) 9. Gavel 75DF, 2.0 lb (8x) 10. Dithane, 2.0 lb (8x); Endura, 3.5 oz (3x); Forum, 6.0 oz (3x) 11. Dithane, 2.0 lb (8x); Scala, 7.0 fl oz (3x); Previcur Flex, 1.5 pt (3x) 12. Actigard, 0.33 – 0.75 oz (6 weekly pre-sprays between mid-June to mid-July); Bravo Ultrex, 1.8 lb (2x), 2.2 lb (2x); Quadris Opti, 1.6 pt (4x) 13. Bravo Ultrex, 1.8 lb (2x), 2.2 lb (2x); Quadris Opti, 1.6 pt (4x) 14. Bravo Ultrex, 1.8 lb (2x); Difenoconazole, 0.34 pt (6x); Mandipropamid, 0.34 pt (3x) Results Due to excessive rain and resulting poor root systems, differences in disease ratings not as pronounced as in previous years No significant differences among treatments for AUDPC of Early Blight on tomato foliage, P=0.151 No significant differences among Total and Marketable fruit numbers, P=0.748 and 0.171, respectively The AUDPC of Early Blight on Tomato Foliage vs. Treatment, 2006 180 160 140 120 100 80 60 40 20 1 2 3 4 Dithane Br/Ranman 9 10 11 12 Dith/Sc/Prev Act/Br/QO 13 14 0 Control Bravo Gavel Dith/End/Forum Br/QO Br/Difen/Mandi Results Unmarketable fruit, P = 0.001 The Control and Difenoconazole/Mandipropamid treatment had significantly more unmarketable fruit than the other treatments Late Blight on Fruit, P = 0.000 The Control and Difenoconazole/Mandipropamid treatment had significantly more fruit with Late blight symptoms than the other treatments Endura/Forum treatment significantly better than Control and Difen/Mandi treatments but significantly more symptomatic fruit than the other treatments The Number of Unmarketable Tomato Fruit vs. Treatment, 2006 60 b b 50 40 30 a a a a 20 a a a a 10 1 2 Control Bravo 3 4 9 10 11 12 13 Gavel Dith/End/Forum Dith/Sc/Prev Act/Br/QO Br/QO 14 0 Dithane Br/Ranman Br/Difen/Mandi The Number of Tomato Fruit Showing Late Blight Symptoms vs. Treatment, 2006 35 c c 30 25 20 b 15 10 ab 5 a 1 2 3 a a 4 9 10 a a a 11 12 13 14 0 Control Bravo Dithane Br/Ranman Gavel Dith/End/Forum Dith/Sc/Prev Act/Br/QO Br/QO Br/Difen/Mandi 8/16 8/17 8/18 8/19 8/20 8/21 8/22 8/23 8/24 8/25 8/26 8/27 8/28 8/29 8/30 8/31 9/1 9/2 9/3 9/4 9/5 9/6 9/7 0.00 0.00 0.00 0.00 1.31 0.07 0.00 0.00 0.00 0.16 0.13 0.02 0.59 1.07 0.85 0.02 0.00 0.05 0.65 0.09 0.00 0.00 0.04 E)Spray 5) Bravo 9)Gavel 10)Forum+Dith 11)Previcur+Dith 14)Difen + Mandi 1ST LB F)2ND LB Ranman Gavel Endura+Dith Scala+Dith Difenoconazole Forum+Dith Previcur+Dith Difen + Mandi Endura+Dith Scala+Dith Difenoconazole 3RD G) Bravo Gavel LB/Fruit H) Br=0;Di=9 Ranman Gavel 0 0 15.0 1.0 34.0 Protectants chlorothalonil EB +++ LB ++++ YES; Mancozeb EB +++ LB +++ YES Scala (pyrimethanil) EB +++; LB = no activity Endura (boscalid) EB +++; LB = no activity (acropetal, translaminar, no vapor phase; blocks spore germ.) difenoconazole EB ++++; LB = no activity Combined activity (EB and LB) 9) Gavel (zoxamide + mancozeb) EB +++; LB ++++ YES 13) Quadris Opti (azoxystrobin + chlorothalonil) EB +++; LB ++++ YES LB specific 10) Forum (Acrobat) EB = no activity; LB +++ 11) Previcur flex EB = no activity; LB ++++ 4-8) Ranman (cyazofamid) EB = no activity; LB ++++ 14) Revus (mandipropamid) EB = no activity; LB +++ (rainfast + penetrant; not systemic; use higher rates and shorter interval) Conclusions – • In 2006 (unusual conditions), all early blight treatments performed equally Bravo, Dithane, Gavel, Dithane + Endura, Dithane + Scala, Bravo 4x/Quadris Opti 4x, Bravo 2x/difenoconazole 6x • During a critical late blight infection period, a LB-effective-product must be included in each regular spray schedule; options are available for LB control • Bravo ++++; mancozeb +++ • Ranman alt. Bravo ++++; Gavel ++++ • Previcur Flex + mancozeb alt. Bravo or mancozeb ++++ • Quadris Opti alt. Bravo ++++ Special considerations Forum + mancozeb need to alternate with Bravo mandipropamid must combine with mz or Bravo and alternate with Bravo (not with difenoconazole)
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