The new late blight genotypes and their management in field trials

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1 The new late blight genotypes and their management in field trials Pamela D Roberts Plant Pathology Department Southwest Florida Research and Education Center Immokalee, FL

2 Late Blight caused by the Oomycete Phytophthora infestans on tomato

3 Symptoms of late blight on potato

4 The new late blight genotypes and their management in field trials Past and current population of P. infestans Has management of late blight changed?

5 Importance of genotyping P. infestans Genotype Genotype is defined as the genetic makeup of an organism Phenotype Host preference (potato/tomato) Fungicide sensitivity Mating type Control Strategies Late blight decision support system (DSS) Fungicide selection Historical epidemiological performance

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7 Special Thanks Glades Crop Care Florida Tomato Committee for funding in 2006 which allowed my program in Immokalee to initiate a program on late blight on tomato

8 Sexual Reproduction Source of New Genotypes Mutation during Asexual Reproduction

9 Genotypes of Phytophthora infestans 24 genotypes identified in USA so far.

10 2014 All isolates characterized from Florida were US-23 Current, preliminary data from rest of US indicate predominantly US-23 Why?

11 Summary of some key characteristics of recent US genotypes of Phytophthora infestans on tomato and potato*. Genotype Host Mating type Sensitivity to mefenoxam US-8 Potato A2 Intermediate to Resistant US-11 Potato/Tomato A1 Resistant US-20 Tomato A2 US-21 Tomato A2 US-22 Potato/Tomato A2 US-23 Potato/Tomato A1 Intermediate to Resistant Sensitive to Intermediate Sensitive to Intermediate Sensitive to Intermediate US-24 Potato A1 Intermediate *Reference Table 1 for sources and usablight.org

12 Summary of some key characteristics of recent US genotypes of Phytophthora infestans on tomato and potato*. US-23 Potato/Tomato A1 Mating Type Sensitive to mefenoxam

13 Late Blight Genotypes in FL Florida appears to follow the same genotype(s) that occur elsewhere in tomato production on east coast Rapid SSR identification of genotype within days of sampling

14 Late Blight Caused by the Oomycete Phytophthora infestans Spores are carried long distances by wind/rain. Cool nights, moderate day temperature, and humidity favor disease development. Sporangia

15 Late Blight Management in Tomato and Potato Use only certified disease-free transplants and tubers Avoid adjacent plantings with older, infected crops Eliminate cull piles and volunteers. Some potato varieties are rate-reducing resistant, tomato resistance not yet available in commercial varieties Scout fields particularly in wetter parts of fields or where spray applications might miss Know when late blight is in your area Use a late blight forecasting system, where available Maintain preventative fungicide schedule with good coverage. Particularly November through March or when late blight has been reported

16 Fungicides : Wide-spectrum, preventative materials These are probably already on plants for control of other fungal and bacterial diseases Chemical (active ingredient) *FRAC Fungicide Group Read a current product label before applying any chemical. Remarks Various Brand Names (Chlorothalonil) M5 Contact activity only; preventative Various Brand Names (Mancozeb) M3 Mixed (mancozeb and copper) for Various Brand Names (Copper) M1 bacterial spot management. Contact only; preventative *Fungicide Resistance Action Committee: Fungicides codes are sorting fungicides by mode of action

17 Fungicides (specific) for Late Blight Chemical (active ingredient) Fungicide FRAC Group Be sure to read a current product label before applying any chemical. Ranman (Cyazofamid) 21 Curzate 60DF (Cymoxanil) Tanos (Cymoxanil + Famoxadone) and 11 Forum (Dimethomorph) 40 Remarks Alternate with non-group 11 chemistry between applications Limit is 7 apps/year. Use in combination mancozeb or chlorothalonil. Do not make more than 2 consecutive applications Revus (Mandipropamid) Revus Top (Mandipromid + Difenoconazole) Zampro (Ametoctradin + Dimethomorph) 45 and 40 Presidio (Fluopicolide) 43 Previcur Flex (Propamocarb) Do not make more than 2 consecutive applications Adjuvant recommended; limit is 3 applications per season Do not make more than 2 consecutive applications; tankmix with another fungicide Tank mix with chlorothalonil or mancozeb Gavel 75DF (Mancozeb and Zoxamide) 22 and M3 See label Does not include all labeled fungicides

18 Fungicides containing mefenoxam (metalaxyl) Phenylamide Chemical (active ingredient) Fungicide Group Be sure to read a current product label before applying any chemical. Remarks Ridomil Gold MZ (Mancozeb; Mefenoxam) M3 & 4 Mefenoxam has been standard Ridomil Gold Copper 64.8W in Phytophthora control; M1 & 4 (Copper hydroxide; Mefenoxam) however Phytophthora has gene(s) for resistance to this Ridomil Gold Bravo SC fungicide group and depending M5 & 4 (Chlorothalonil; Mefenoxam) upon genotype present, may or may not be resistant

19 Plots of tomato plants within same trial: fungicide not effective vs highly effective fungicide control of late blight

20 2014 Trial (27 trts) Trt Fungicide Rate FRAC Dates Applied A B C D E F G H I J K 1 Untreated Control (water) 2 Bravo WeatherStik 6SC 1.5 pt/a M5 A,B,C,D,E,F,G,H,I, J, K 3 Bravo WeatherStik 6SC 1.5 pt/a M5 ABCEGIK Induce 0.125% v/v S DFHJ Revus Top 7 fl oz/a 40 & 3 DFHJ 4 Ranman Zampro 2.75 oz/a 21 DFHJ 14 oz/a 45 & 40EGIK Bravo WeatherStik 720 (2 pt/a) M5 ABC * L B A= 25 Feb; B= 4 Mar; C= 11 Mar; D= 14 Mar; E= 18 Mar; F= 25 Mar; G= 31 Mar; H=1 Apr; I=8 Apr; J=15 Apr; K=21 Apr

21 AUDPC Management of late blight by selected treatements, spring 2014

22 AUDPC Management of late blight by selected treatements, spring 2014

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24 Summary Untreated plants and fruit were severely affected usually within a week of first detection of late blight lesions After 14 days, unprotected plants were more than 60% defoliated Fungicide applications should not be delayed Protectant fungicides used prior to late blight such as chlorothalonil (highly effective), mancozeb, and copper (less effective) Other fungicides used protectively with wide spectrum of activity may also protect from late blight When weather is highly conducive (high relative humidity; (fog; rain; leaf wetness period longer than 6 hours; cool temperatures) and late blight is established Use fungicides specific to late blight May need to shorten application intervals

25 Late Blight of Tomato and Potato: Recent Occurrences and Management Experiences Webinar USABlight Webinar was held on January 14th, 2014 Chris Smart Cornell University Meg McGrath Cornell University Pam Roberts niversity of Florida Beth Gugino The Pennsylvania State University Amanda Gevens University of Wisconsin This project was supported by the Agriculture and Food Research Initiative Competitive Grants Program Grant from the USDA National Institute of Food and Agriculture.

26 Webinar: Organic/Homeowner 2012 Treatments-FL Trt Fungicide Untreated Control (water) Rate Dates Applied A B C D E F A,B,C,D,E,F Bravo WeatherStik 720 (chlorothalonil) 1.5 pt/a A,B,C,D,E,F Actinovate AG 0.03% Streptomyces lydicus WYEC oz/a A,B,C,D,E,F Day 0, +8, +15, +22, +29, +36 Tomato FL47 transplanted on January 11 A= 24 Jan; B= 1 Feb; C= 8 Feb; D= 15 Feb, E= 22 Feb, F= 29 Feb Late blight first observed on February 17 L B

27 Disease Severity Disease Severity for Late Blight on Tomato, 2 Mar 2012, Florida A P = B* C *Similar results with Actinovate AG at 12 oz/a were obtained in 2008

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30 Cornell Late Blight Decision Support System (DSS) (Fry et al.)

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32 Disease forecasting as a tool for late blight management Cornell Late Blight Decision Support System (DSS) (Fry et al.) More comprehensive tool containing: 1. Location-specific weather data (number of partners) 2. Disease forecasting tools based on: Blitecast and Simcast (blight units, fungicide units and accounts for host resistance) 3. Late blight disease simulator 4. Alerts ( or text)

33 30-Year Average High and Low Temperatures for Immokalee F Maximum Minimum Optimum high and low temps for P. infestans

34 30-Year Average High and Low Temperatures for Immokalee F Foggy mornings= adequate moisture Maximum Minimum Optimum high and low temps for P. infestans

35 Evaluation of a DSS for fungicide applications on very susceptible FL47 and moderately susceptible Legend tomato, 2014 AUDPC FL 47 Legend Untreated Weekly DSS Untreated= no sprays 7 day full season= 11 sprays all chlorothalonil DSS= Cornell Decision support system= 7 sprays for FL 47 and 4 for Legend

36 Late blight has been occurring more often in recent years, esp. on tomato in the NE and Midwest. Expected to continue. New pathogen genotypes; affect disease occurrence. Both mating types of the pathogen are in the U.S; sexual reproduction is a concern. USABlight website provides current information on late blight occurrence; other topics as well. Decision Support System (DSS) proved useful for timing fungicide applications to maximize control. Parts of this project was supported by the Agriculture and Food Research Initiative Competitive Grants Program Grant from the USDA National Institute of Food and Agriculture.

37 Acknowledgements Charlie Mellinger, Galen Frantz, Leon Lucas and other personnel at Glades Crop Care Sonia Tighe, Executive Director, Florida Specialty Crop Foundation SWFREC: Jessie Watson, Ryan Donahoo, Jacob Collins Collaborators (Smart, McGrath, Gevens, Everts, Gugino, Fry, Ristaino) and funding from USDA Specialty Crops and USDA -AFRI