Antigo Area Early 5/13 6/ /29/13

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1 Vegetable Crop Update A newsletter for commercial potato and vegetable growers prepared by the University of Wisconsin-Madison vegetable research and extension specialists No. 10 July 1, 2013 In This Issue DSVs (Disease Severity Values)/Blitecast for late blight management PDays for early blight management Cucurbit downy mildew Phytophthora crown and fruit rot on cucurbit and solanaceous crops Calendar of Events July 23 UW-Hancock Ag Research Station Field Day, Hancock, WI (tentative agenda begins at noon) Aug 22 UWEX-Langlade County Airport Research Station Field Day, Antigo, WI Vegetable Disease Update Amanda J. Gevens, Assistant Professor & Extension Vegetable Plant Pathologist, UW-Madison, Dept. of Plant Pathology, (office), gevens@wisc.edu. Vegetable Path Webpage: Current P-Day (Early Blight) and Severity Value (Late Blight) Accumulations P-Day of 300 indicates threshold for early blight risk and triggers preventative application of fungicide. DSV of 18 indicates threshold for late blight risk and triggers preventative application of fungicide. Red text in table below indicates threshold has been met. NA indicates that information is not yet available as emergence has yet to occur. Location Planted 50% Emergence P-Day DSV Cumulative Calculation Date Cumulative Antigo Area Early 5/13 6/ /29/13 Grand Marsh Area Mid 5/22 6/ /29/13 Late NA NA NA NA NA Early 4/15 5/ /29/13 Mid 5/1 5/ /29/13 Late 5/15 6/ /29/13 Hancock Area Early 4/20 5/ /29/13 Mid 5/5 5/ /29/13 Late 5/15 6/ /29/13 Plover Area Early 4/22 5/ /29/13 Mid 5/7 5/ /29/13 Late 5/24 6/ /29/13 DSVs and Late Blight: From in-potato-field weather stations here in Wisconsin, we have far exceeded initial threshold for Blitecast in all monitored locations with the exception of mid and late planted fields in the Antigo area. Across all locations, accumulations were great this past week with much disease-favorable weather (and reports of late blight in fields). As such, a 5 to 7-day fungicide program is appropriate at this time. The UW Vegetable Pathology site offers the Blitecast and Tomcast accumulations for foliar disease control from remotely sensed and forecasted weather data. Information is provided to help growers interpret the information offered for potato and carrot disease control. The link is

2 entitled: NEW: Blitecast & Tomcast estimates (from remotely sensed weather data), 2013 right in the center of the home page of: Late blight status in WI and the U.S. Late blight was confirmed in Adams County Wisconsin on Friday June 28 on potato (US-23). A second confirmed report came today from Juneau County Wisconsin on potato. We will genotype and provide an update within a day or so. There were reports of late blight on tomato in New Jersey and Kentucky over the last two weeks. To date this production year, late blight has been reported in in FL, TN, WV, LA, NJ, MD, KY, and WI. The website: indicates location of positive reports of late blight in the U.S. and provides further information on disease characteristics and management. PDays and Early blight: P-Days have reached/surpassed the threshold of 300 in early plantings at Grand Marsh, Hancock, and Plover. Fungicide applications for the management of early blight are recommended at this time for early planted fields in Central and Southern Wisconsin. Because of the dual risk of late and early blight, consider management options that control against both diseases. Cucurbit Downy Mildew: has not been identified in Wisconsin at this time in commercial fields, home gardens, or our sentinel monitoring plots. DE, AL, MD, SC, FL, GA, TX, and NC have reported cucurbit downy mildew this season across multiple cucurbit hosts. I will be keeping tabs on disease reports in the region and will provide updates in this newsletter. No forecasted risk of movement of spores from states reporting detects to Wisconsin at this time. The website: offers up to date reports of cucurbit downy mildew and disease forecasting information. Phytophthora crown and fruit rot in Cucurbits, Peppers, and Tomatoes: Over the past few years, many Wisconsin producers battled Phytophthora crown and fruit rot in vegetable crops. The disease has again been identified on cucurbits in Wisconsin. This potentially aggressive disease, caused by the soilborne water mold Phytophthora capsici, can infect a broad range of crops including summer squash, zucchini, winter squash, pumpkins, melons, cucumbers, peppers, tomatoes, and eggplant. Over the past few years, reports of this pathogen have also been made on snap and lima beans in commercial fields in the Midwest and Mid-Atlantic regions of the U.S. Symptoms of Phytophthora include water-soaking of lower stem or crown of a plant resulting in complete wilting of plants, and water-soaking on fruit often associated with white talcum-like pathogen sporulation on surfaces (see pictures below). Breakdown of plant tissues by this pathogen can be rapid and can occur on fruit post-harvest. To avoid Phytophthora, the following measures should be taken: do not plant susceptible crops on fields with recent history of this disease, provide good drainage (raised beds are beneficial), avoid planting in low-lying areas of fields, practice good irrigation management to avoid standing water and extended periods of leaf wetness, apply effective protectant fungicides when conditions favor infection in known infested fields. With dense cucurbit plant canopies and sporadic rains (especially overnight rains in southern WI), it is critical that growers of susceptible crops scout their vegetable fields for Phytophthora. Roguing of infected plants from the production field when disease is identified early can aid in limiting spread. Do not allow infected fruit to sporulate and persist in production fields. Culls can continue to provide inoculum for remaining plants. Because Phytophthora is soilborne, soil from infested fields remaining on equipment should be

3 % resistant to mefenoxam removed prior to moving to a new or clean field. Every effort should be made to avoid introducing this pathogen into uninfested fields. Fungicides can be effective in managing Phytophthora when environmental conditions favor disease. The keys to making fungicides work best for you are: 1) select most effective fungicides with no known resistance in your field/area, 2) make a thorough application particularly if fruit are to be protected and are beneath a dense foliar canopy, and 3) make frequent applications when conditions favor disease and crop growth is rapid. Some fungicides have registered use in drip irrigation systems which may aid in disease control at root and lower stem zones (ie: Presidio). There are reports of P. capsici resistance to the fungicide mefenoxam (active ingredient in Ridomil Gold, Ultra Flourish) in Wisconsin and other vegetable-producing states. My program tested several isolates of P. capsici from Wisconsin production fields in 2010 and 2011 and determined that individual fields had unique mefenoxam resistance profiles, likely as a result of different field histories and fungicide use patterns. In the above graph, fields 1, 2, 3, and 4 had 30-90% resistance to mefenoxam, indicating intermediate resistance (mefenoxam may not provide complete control of Phytophthora crown and fruit rot). Two fields, 5 and 6, had mefenoxam-sensitive P. capsici isolates, indicating sensitivity (mefenoxam should work to control the disease). Unique fields sampled in Central WI, This percentage is calculated based on the relative growth of the pathogen on mefenoxam-free media relative to media amended with 100 ppm mefenoxam. The categorization of resistant (>90%), intermediately resistant (30-90%), and sensitive (<30%) is established in the research of this pathogen and has been correlated to disease response on plants treated with the fungicide. If your farm has no history of mefenoxam (ie: Ridomil) use, it is likely that the fungicide will be effective for disease control. Please contact me if you have questions on resistance or need assistance in determining this status. Fungicides with activity against Phytophthora crown and fruit rot include: Ridomil (mefenoxam), Ranman (cyazofamid), Forum (dimethomorph), Tanos (fanoxadone + cymoxanil), Presidio (fluopicolide), Aliette (fosetyl-al), Revus (mandipropamid), and Gavel (zoxamide + mancozeb). Fungicides should be tank-mixed with multi-site protectant such as chlorothalonil (ie: Bravo) or mancozeb (ie: Dithane). Tank-mixes of Presidio (fluopicolide) or Revus (mandipropamid) with copper hydroxide (ie: Kocide) have also been effective in trials on

4 picking cucumber in Michigan (see link below). If you have any questions on symptoms, control, or fungicide resistance, please contact your county agent, crop consultant, the diagnostic clinic, or myself at UW-Plant Pathology. For further information on any fungicides that may be mentioned in this newsletter, please see the 2012 Commercial Vegetable Production in Wisconsin Guide A3422. An online pdf can be found at the link below or a hard copy can be ordered through the UWEX Learning Store. A B C D Phytophthora crown and fruit rot pictures include A: disease cycle on cucumber, B: symptoms on winter squash fruit, C: wilting symptom on winter squash plants, and D: fruit rot and sporulation on cucumber fruit. The 2013 A3422 Commercial Vegetable Production in Wisconsin guide is available for purchase through the UW Extension Learning Store website: Vegetable-Production-in-Wisconsin2013-P540.aspx A pdf of the document can be downloaded or is available at the following direct link:

5 Vegetable Crop Update A newsletter for commercial potato and vegetable growers prepared by the University of Wisconsin-Madison vegetable research and extension specialists Disease Supplement No. 2 June 28, 2013 Vegetable Disease Update Amanda J. Gevens, Assistant Professor & Extension Vegetable Plant Pathologist, UW-Madison, Dept. of Plant Pathology, (office), gevens@wisc.edu. Vegetable Path Webpage: Late blight has been detected on potato in Adams County Wisconsin. We have not yet characterized the strain, but will be working on this over the next few. Most late blight identified in the U.S. this year has been of the US-23 clonal lineage and I would suspect this is the type collected in Adams County just today. At this time, with the wet weather, it is critical that preventative fungicide applications are made to protect susceptible tomato and potato crops from late blight. A shortened 5-7 day spray interval is recommended. A second file listing registered fungicides for potato late blight in Wisconsin is included as a companion to this newsletter (& will be accessible at Veg Path website above). Clonal lineage Mating type Optimum growth temp Host comments Years found in WI Resistance to mefenoxam US-22 A2 24ºC Tomato and potato, poor pathogen on pepper, eggplant, tomatillo US-23 A1 18ºC Tomato and potato 2009, , 2011, 2012 Sensitive Intermediately resistant US-24 A1 20ºC potato 2010, 2011 Intermediately resistant esistant (variability among isolates) Nationally, there has been a recent report of late blight in the U.S. in NJ on tomato. This Disease Supplement serves to make growers aware that late blight has been identified in Wisconsin and preventative fungicide application is recommended for producers of susceptible potato crops at all crop stages. The website: indicates location of positive reports of late blight in the U.S. and provides further information on disease characteristics and management. Additional, specific fungicide recommendations will soon be provided through this newsletter for tomato and organics.

6 In order to help better understand the epidemic at hand, please submit samples to my lab or work through your county agent and request that they send to me for genotyping. All we need to know is the county of sample origin, we do not need to have specific field or grower information associated with the sample. Identification of genotype at the county level would be very helpful in improving our understanding of this epidemic and potential future risks. Lab address is: Amanda Gevens, 1630 Linden Dr, Room 689, Plant Pathology Dept., University of Wisconsin, Madison, WI Please send infected leaves in a slightly inflated ziplock bag with no paper towel. Overnight shipping is best. Further information on late blight and its management can be found in the Vegetable Crop Updates newsletters archived at the University of Wisconsin Vegetable Pathology Website. Also, fact sheets on late blight are available under the Late Blight tab at the website. Further details on registered fungicides for WI vegetables can be found in the Wisconsin Commercial Vegetable Production Guide A3422, Comparison of Late Blight Fungicides (highest rates registered) Provided by Dr. Steve Johnson, University of Maine Cooperative Extension In addition to the products listed below in table, others may be available and effective; not a comprehensive list. Effectiveness Mode of action Product Leaf blight New growth Stem blight Tuber blight Protectant Curative Antisporulant Rainfastness Mobility in the plant FRAC # REI PHI Bravo etc G No P No G No No G contact M Curzate + Dithane etc G? F No G E P G translaminar + contact 27 + M Dithane etc G No P No G No No F contact M Forum + Dithane G? F F G P G G translaminar + contact 40 + M Gavel E No P F E No No G contact + contact Kocide etc P No P No F No No P contact M Omega E No P G E No No G contact Previcur Flex + Dithane etc G G G No G G G E systemic + contact Ranman E No P E E No No E contact 21 translaminar Tanos G? F No G E P G + contact 11 translaminar Revus Top E? F G E P F E + contact Tin E No E E G No E F contact M1 No=No effect; P=Poor; F=Fair; G=Good; E=Excellent;?=Unknown M

7 Page 1 Potato Late Blight Fungicides Registered for WI, In-furrow and seed treatment registrations are omitted. This is not a comprehensive list. Most fungicides listed are for use in conventional production systems. List compiled 4 June Amanda J. Gevens, Extension Plant Pathologist, UW-Madison Office Phone: ; gevens@wisc.edu Trade Name (rate/a) Agri Tin, Super Tin 4L, Super Tin 80WP (4-6 fl oz) Alude (1.25 qt in 90 gal water) Fosphite, Rampart (1-4 qt in at least 20 gal water/a) Fungi-Phite (Foliar: 2 qt/a Seed trt: 15% volume to volume-2 ton in 1 gal solution) Badge SC (1-3 pt at 7-10 day interval) Bravo Ultrex (.7 then.9 to 1.36 lb) Bravo WeatherStik, Echo 720, Equus 720 SST, Initiate 720, Chlorothalonil 720 SC (.75 then pt) Bravo Zn, Equus 500 Zn (1 1/8 then 1 1/5 to 2 ¼ pt) Echo Zn (1 to pt) Equus DF (.7 then.9 to 1.36 lb) Active Ingredient(s) triphenyltin hydroxide mono and dipotassium salts of phosphorous acid potassium phosphite potassium phosphite PHI REI FRAC # Comments 7 48 hours 30 Restricted use pesticide. 3 fl oz rate can be used if material is tank-mixed with another fungicide. 0 4 hours 33 Foliar application 0 4 hours 33 Foliar post-emergence spray and post harvest spray for control in storage. 0 4 hours 33 Seed piece spray and foliar post-emergence spray. Tank-mix with another effective fungicide is recommended and use high label rate for late blight control. copper hydroxide, copper oxychloride 0 24 hours M1 Protectant activity only. chlorothalonil 7 12 hours M lb a.i./acre maximum on standard label. However, WI has a special 24(c) registration for long season potatoes extending the max a.i. from to 16 lb a.i./acre with Bravo (Syngenta) and Echo (Sipcam Advan) formulations. Echo 90DF (5/8 then 7/8 to 1.25 lb) Cabrio Plus (2.9 lb) pyraclostrobin+m etiram 3 24 hours 11+M lb/acre maximum per season. Do not apply more than 2 sequential applications.

8 Page 2 Potato Late Blight Fungicides Registered for WI, Trade Name (rate/a) Champ WG (1 to 1.5 lb 3 to 4 lb in severe areas) Active Ingredient(s) copper hydroxide PHI REI FRAC # 0 24 hours M1 Comments Use high label rates for foliar late blight protection. Champ Formula 2 Flowable (2/3 to 2 2/3 pt) Champ DP Dry Prill (2/3 to 1 lb 2 to 2 2/3 lb when disease is severe) Kentan DF (1-2.5 lb 4 lb when severe) copper hydroxide 0 24 hours M1 Use high label rates for foliar late blight protection. Kocide 2000, Kocide 3000 (.73-3 lb lb) Nu-Cop 3L (2/3 to 2 pt 2 to 4 pt if severe) Nu-Cop 50DF (1-1.5 lb 3-4 lb if severe) C-O-C-S WDG (1.5-4 lb) Curzate 60DF (3.2 oz foliar) Dithane F45 Rainshield (.4 to 1.6 qt) copper oxychloride, basic copper sulfate 0 24 hours M1 Use high label rates for foliar late blight protection. cymoxanil hours 27 Locally-systemic fungicide. Must be tankmixed with a protectant fungicide. Rainfast within 2 hours. mancozeb 24 hours 3 M3 Max rate per acre/season is 11.2 lb a.i. Plant as soon as possible after seed treatment. Dithane M45 (.5 to 2 lb) Roper DF Rainshield (1-2 lb)

9 Potato Late Blight Fungicides Registered for WI, Trade Name (rate/a) Evito 480SC, Aftershock (3.8 fl oz) Forum (Foliar and tuber control: 6 oz) Gavel 75DF (1.5 to 2 lb) Gem 500SC (3.8 fl oz) Headline (6 to 12 fl oz) ManKocide (1.5 to 2 then 4-5 lb) Omega 500F (5.5 fl oz) Omega Top MP (5.5 fl oz) individual label for Omega sold in co-pack with Top MP (difenoconazole) Oxidate (40 to 120 fl oz to 100 gal water, gal solution per acre Penncozeb 80WP, Penncozeb 75DF (.5 to 2 lb) Active Ingredient(s) PHI REI FRAC # Comments fluoxastrobin 7 12 hours 11 Follow label for resistance management. dimethomorph 4 12 hours 40 May be tank-mixed with another effective fungicide for enhanced management but not required by label. Addition of an adjuvant may enhance management. Can be applied after vine kill. zoxamide+manco zeb 3 48 hours 22+M3 Do not make >6 applications/crop. Contact fungicide. trifloxystrobin 7 12 hours 11 Follow label for resistance management. pyraclostrobin 3 12 hours 11 Follow label for resistance management. mancozeb+copper hydroxide 3 24 hours M3+M 1 Not labeled as a seed trt for potatoes. fluazinam hours 29 REI is 4 for high exposure activities. New special local need label 24c in April fluazinam hours 29 Can be applied aerially. REi is 4 for high exposure activities. hydrogen dioxide 0 1 hour NC Foliar spray for late blight. Frequent applications (5-day intervals) can limit sporulation. mancozeb 3 24 hours M3 Do not exceed 11.2 lb a.i./acre/year. Penncozeb 4FL, Manzate flowable (.4 to 1.6 qt) Manzate Pro- Stick (1 to 2 lb, seed trt: 1.25 lb/50 gal water) Phostrol (2.5 to 10 pt) (Post harvest trt: 1 gal/ton in.5 gal water) mono- and dibasic sodium, potassium, and ammonium phosphites 0 4 hours 33 Can be applied as a foliar for late blight, pink rot, and Pythium leak. Can be applied postharvest for storage disease control. Page 3

10 Page 4 Potato Late Blight Fungicides Registered for WI, Trade Name (rate/a) Polyram 80DF (1.5 to 2 lb in 15 gal water/acre minimum) Previcur Flex (.7 to 1.2 pt) Priaxor (4-8 fl oz) Quadris (6 to 15.5 fl oz) Quadris Opti (1.6 pt) Ranman (1.4 to 2.75 fl oz) Reason (5.5 to 8.2 fl oz) Revus (5.5 to 8 fl oz) Revus Top (5.5 to 7 fl oz) Tanos (8 to 10 oz) Ridomil Gold SL (1 to 2 pt) Ridomil Gold Bravo SC (2.5 pt) Ridomil Gold Copper (2 lb) Ridomil Gold MZ WG (2.5 lb) Zampro (11-14 fl oz) Active Ingredient(s) PHI REI FRAC # Comments metiram 3 24 hours M3 Metiram is an EBDC, like mancozeb (M3). Total amount of a.i. per year/acre must include all EBDCs. propamocarb hydrochloride fluxapyroxad+pyr aclostrobin hours F Apply in a tank-mix with effective protectant. Can be applied as a broadcast or banded application over the row, post-emergence hours 7+11 Cannot apply more than 3 applications/season. Follow label for resistance management. Xemium and Headline pre-mix. azoxystrobin 14 4 hours 11 Alternate away from Group 11 fungicides to manage resistance. azoxystrobin+chl orothalonil hours 11+M5 Alternate away from Group 11 fungicides to manage resistance. cyazofamid 7 12 hours 21 Follow label for resistance management. fenamidone hours 11 Follow label for resistance management. mandipropamid 14 4 hours 40 Addition of an adjuvant is recommended. mandipropamid+d ifenoconazole cymoxanil + famoxadone hours 40+3 Addition of an adjuvant is recommended hours Must be tank-mixed with an effective protectant fungicide. mefenoxam hours 4 Do not apply beyond the at-planting stage. mefenoxam+chlor othalonil mefenoxam+copp er hydroxide mefenoxam+man cozeb ametoctradin+dim ethomorph hours 4+M5 Follow label for resistance management hours 4+M1 Tank-mix with an effective protectant hours 4+M3 Follow label for resistance management hours Do not make more than 2 sequential applications. Follow label for resistance management. Ametoctradin is new a.i.; dimethomorph is Forum (formerly Acrobat).

11 Managing Late Blight in Organic Tomato & Potato Crops Amanda J. Gevens Extension Plant Pathologist, University of Wisconsin, Madison, WI Phone: (608) , Updated June 28, 2013 with contributions from UW-Plant Pathology doctoral research of Anna C. Seidl Disease Description & Status of Disease in WI: Late blight is a potentially destructive disease of tomatoes and potatoes caused by the fungal-like organism, Phytophthora infestans. This pathogen is referred to as a water mold since it thrives under wet conditions. Symptoms of tomato or potato late blight include leaf lesions beginning as pale green or olive green areas that quickly enlarge to become brown-black, water-soaked, and oily in appearance (Figure 1). Lesions on leaves can also produce pathogen sporulation which looks like white-gray fuzzy growth (Figure 1, 2). Stems can also exhibit dark brown to black lesions with sporulation. Fruit symptoms begin small, but quickly develop into golden to chocolate brown firm lesions or spots that can appear sunken with distinct rings within them (Figure 2); the pathogen can also sporulate on tomato fruit giving the appearance of white, fuzzy growth. The time from first infection to lesion development and sporulation can be as fast as 7, depending upon the weather. In WI, late blight has been identified on tomatoes and potatoes since in each of the last 4 years. On June 28, 2013, we confirmed late blight on potato in Adams County, Wisconsin. It is important to protect susceptible crops with fungicides in both conventional and organic production systems. A B C Figure 1. Symptoms of late blight on potato tuber and leaves. A. Note brown-rust colored firm discolored tuber tissue. B. Late blight lesion on potato leaf. Lesions appear brown and papery when weather turns dry or after fungicide use. C. Underside of leaf showing late blight pathogen producing spores. A B C D E Figure 2. Symptoms of tomato late blight on tomato leaves and fruit. A. Entire row of plum tomatoes with dead foliage due to late blight. B. Brown, firm, late blight lesions on Roma tomato fruits. C. Late blight lesion on tomato leaf. Note brown, water-soaked lesion with white pathogen sporulation. D. Close up of brown, firm, late blight lesion on green tomato fruit. E. Sporulating late blight lesion around the stem and shoulders of a ripening tomato fruit.

12 Management: We know that the strain of Phytophthora infestans isolated from Adams County potato is type US-23 which is known to be aggressive on potato and tomato, and is of the mating type A1. We have only seen late blight of type US-23 on potato in WI at this time. In our research, we have demonstrated that the US-23 type will infect tomato, potato, hairy nightshade, black nightshade, and petunia; select cultivars of eggplant, pepper, and tomatillo did not become infected. US-23 produces roughly twice as many spores per lesion as other late blight genotypes and has great potential to rapidly reproduce and spread. Some cultivars have resistance to late blight and are listed in Table 1. Note cultivars containing both Ph-2 and Ph-3 resistance genes are most resistant. Several varieties also exhibit some resistance including Pruden s Purple and Matt s Wild Cherry. Potato cultivars with some resistance to late blight include Jacqueline Lee, Defender, and Satina. The disease forecasting tool (Blitecast) indicates risk times for late blight activity and can aid in identifying critical times for preventative fungicide applications. To access Blitecast information for Wisconsin, please go to: Once late blight has moved into a region, it is critical that tomato and potato plants be protected. Fungicides must be present on foliage in order to have a protective, disease-limiting effect. Because new growth is not protected and fungicides can wash off, repeat sprays are necessary. Little disease control can be had when fungicide applications are made only after disease onset. A 2007 study compared copper and non-copper containing organic-approved fungicides (such as Sonata, Serenade, and Oxidate) for late blight control on potato. Results from replicated trials showed that the best organic-approved fungicide for potato late blight control was copper (Dorn, et al Control of late blight in organic potato production: evaluation of copper-free preparations under field, growth chamber, and laboratory conditions. Eur. Journal of Plant Pathology 119: ). Copper containing fungicides have provided some of the best preventative control against late blight in multiple U.S. trials in recent years as well. Table 2, below, lists some of the certified organic copper formulations. In the past 2 years, we ve been investigating efficacy of non-copper organic fungicides and have demonstrated good control of tomato late blight with EF-400 under laboratory conditions. Dr. William Kirk of Michigan State University has conducted field trials with EF-400 plus ExCit (now BacStop) on potatoes and corroborated our laboratory efficacy results. Good field control of potato late blight was demonstrated with weekly applications of EF non-ionic surfactant for 8 weeks. Further information on these organic products can be found at: We tested several organic fungicides (and made a few conventional comparisons) (Figure 3 below). Zonix (a rhamnolipid from Jeneil Biosurfactant Company) and EF400 (US Agritech) performed well when applied before inoculation (prior to disease onset). Fungicides have the best chance of effectively managing disease when applied before disease starts this is true for all fungicides, conventional and organic. While Oxidate didn t perform well, keep in mind that it is a contact antisporulant and will kill spores on contact, but will not provide lasting control as a protectant. It has a place to manage spore load, but can t be relied upon solely to prevent late blight. Late blight can be managed in an organic system, but control measures need to be proactive. In the circumstance when late blight gets out of control, early harvest and crop destruct options must be considered to limit development of inoculum that could pose heightened risk for area producers. This is a community disease management by all growers of susceptible crops is necessary.

13 Table 1. Tomato cultivars tested for late blight resistance against the US-22, US-23, and US-24 clonal lineages of Phytophthora infestans and their resistance/susceptibility response. Cultivar v Selection Parameter w AUDPC Lesion Length x AUDPC Pathogen Growth y US-22 US-23 US-24 US-22 US-23 US-24 Wapsipinicon Field observation 80.5a z 116.2a 12.6a 72.5a 155.0bcd 0.0a Mountain Magic Ph-2 and Ph ab 67.1a 49.8ab 73.8a 22.5a 27.5ab Matt s Wild Cherry Seed company 87.6ab 128.7ab 22.2ab 70.0a 118.8ab 10.0a Pruden s Purple Other research 177.0abc 153.0ab 48.4ab 180.0ab 136.3abc 20.0ab Legend Ph cd 161.5abc 79.2abc 271.3bc 201bcde 96.3abcd Plum Regal Ph cde 137.5ab 110.6bc 206.3b 147.5bcd 106.3abcd Juliet Seed company 180.0bc 214.0bcd 108.2abc 228.8b 246.3cdef 150.0cd Roma Field observation 257.3cde 251.8cd 81.7abc 272.5bc 261.3def 48.8abc Slava Other research 249.3cde 277.1d 100.5abc 271.3bc 293.8ef 136.3bcd Green Zebra Other research 321.0e 295.5d 114.9bc 365.0c 322.5f 152.5cd Brandywine Red Susceptible control 293.7de 304.1d 160.9c 268.8bc 285.0ef 205.0d v Mountain Magic, Plum Regal, and Juliet are hybrids. Legend was bred to contain Ph-2 resistance, but is open pollinated, so is considered an heirloom by some. The remaining cultivars are heirlooms. w Cultivars were selected based on anecdotal field observations from 2009, claims by seed companies of late blight resistance, field trials using other P. infestans clonal lineages (12, 32) or the presence of resistance genes Ph-2 and/or Ph-3. x Lesion length was measured at 0, 5, 7, and 9 after inoculation and area under the disease progress curve (AUDPC) was calculated. y Percent leaf coverage of pathogen growth was determined at 0, 5, 7, and 9 after inoculation and area under the disease progress curve (AUDPC) was calculated. z Values in each column followed by the same letter are not significantly different (Tukey test, P=0.05). Table 2. List of OMRI approved copper fungicides. Please note that this list is not comprehensive, but rather represents those most commonly used and likely available copper formulations. Check with your certifying agency if you have any questions or concerns with product selection. Copper product (OMRI approved) Champ WG COC WP Cueva Fungicide Concentrate Cueva Fungicide Ready-To-Use Nordox 75 WG Nu Cop 50 WP PHT Copper Sulfur Dust Basic Copper 53 Copper Sulfate Crystals Quimag Quimicos Aguila Copper Sulfate Crystal Manufacturer NuFarm Americas, Inc. Albaugh, Inc. W Neudorff GmbH KG W Neudorff GmbH KG Nordox AS Albaugh, Inc. J.R. Simplot Company Albaugh, Inc. Chem One, Ltd. Fabrica de Sulfato El Aguila, S.A. de C.V.

14 Figure 3. Comparison of common organic and comparative conventional fungicides for the control of tomato late blight (US-23 genotype) when applied before and after pathogen inoculation. Frequently asked questions Where did this late blight come from? It may have come from late blight-infected potato seed. Other potential sources may be infected tomato transplants or airborne spores from the region. At this time, national reports of late blight have come from NJ, MD, FL, TN, WV, and LA. The website: indicates location of positive reports of late blight in the U.S. and provides further information on disease characteristics and management. Where can I find more information on tomato late blight symptoms and management? How do I destroy and/or dispose of my late blight-infected tomato plants? There are several methods of destroying infected plants: 1) pull up plants by the roots, bag, leave in the sun for a few for plant and pathogen to die, and put out for trash pickup. This method is OK for a few plants. 2) For many infected plants, plants can be cut at the base and allowed to die in place. Once plants are dead, you can go in and remove stakes, strings, and plastic and dead plant material can be incorporated into the soil. Shallow incorporation of debris is recommended to avoid creating a warm, sheltered environment which would keep the plant tissue and pathogen alive for extended periods of time beneath the soil surface. 3) Plants can be flame-killed with a propane or other torch; and 4) infected

15 plants can be pulled and placed in a small pile covered over with a dark colored plastic tarp and left in the sun. This will create heat in the pile from the sun beating on the plastic tarp and plants will die within a few. The winter will provide an excellent freeze kill for exposed infected plants. Do not compost late blight infected plant material, as many piles may have warm centers that can allow plant material and the pathogen to remain viable. The goal is to kill the plants and this will kill the pathogen. Are tomato fruits from late blight infected tomato plants safe to eat? Healthy-appearing fruit from late-blight-infected tomato plants are safe for human consumption. If they have been infected, but aren't yet showing symptoms, they won't keep in storage. There are some concerns about canning infected fruit because bacteria can enter late-blight infected fruit and impact quality. UW-Extension food science extension specialist, Dr. Barbara Ingham recommends avoiding canning tomatoes that exhibit late blight infection. Further information can be found at: How fast will late blight infected plants die? This depends upon how many points of infection the plant received, the cultivar (some cultivars are more susceptible than others), the history of use of protectant fungicides (such as copper), and on the weather. Hot, dry, sunny weather typically holds back late blight; whereas cool, rainy, overcast weather will cause late blight to progress rapidly killing the plant in 7 to 10. I have tomato late blight in my garden will I get it next year if I plant tomatoes again? The strain of the late blight pathogen that we currently have in WI cannot survive outside of living plant tissue. Our strain or type of late blight is US-23 which is known to be an A1 mating type. What does this mean? Much like we have male and female mating types in our human population, the late blight pathogen requires an A1 and A2 mating type to be present together to form persistent, overwintering, long term spores (oospores). Oospores can persist in soil for many years. However, without a compatible mating type in WI (we do not have any A2 strains at this time), there are no oospores produced and there is no risk of this season s late blight residing in the soil over winter. To reiterate, the late blight pathogen that we currently have in WI will not overwinter in the soil on its own. It requires living plants or plant parts to remain viable and infective. Therefore, it is critical to kill infected tomato plants and plant parts such as fruit. Potato tubers can also serve as a source of overwintering inoculum and should also be destroyed if found to be infected with the late blight pathogen. Can late blight be seedborne in tomatoes? Generally, the late blight pathogen is not considered a seedborne pathogen in tomato.

16 Vegetable Crop Update A newsletter for commercial potato and vegetable growers prepared by the University of Wisconsin-Madison vegetable research and extension specialists Disease Supplement No. 3 July 3, 2013 Vegetable Disease Update Amanda J. Gevens, Assistant Professor & Extension Vegetable Plant Pathologist, UW-Madison, Dept. of Plant Pathology, (office), gevens@wisc.edu. Vegetable Path Webpage: Late Blight Update: Since the initial late blight detection on commercial potato on June 28 th, there have been two additional counties with confirmed late blight: Juneau on commercial potato on June 29 th and Sauk on home garden tomato on July 2 nd. All late blight has been genotyped as US-23. At time of diagnosis, potato late blight lesions appeared to be 5 to 7 old with pathogen sporulation evident on leaf undersides. Lesions were few throughout field and on leaves only no symptoms on stems. On tomato, late blight lesions appeared to be several weeks old with large oily black lesions on stems and leaves, and sunken sporulating lesions on ripe and unripe fruit. It is challenging to know with certainty where initial inoculum may have come from. However, symptom presentation in potato fields was not suggestive of a seedborne source. No stem lesions were observed and incidence of lesions across field suggested deposition by spore shower. No potato volunteers have been noted so far this season to suggest this potential source. Cull piles are tightly controlled by potato operations and do not appear to be the source. At this time, it is critical that preventative fungicide applications are made to protect susceptible tomato and potato crops from late blight. A shortened 5-7 day spray interval is recommended. Registered fungicides for potato late blight in WI are listed at the UW Vegetable Pathology website. US-23 can be managed with mefenoxam fungicides. Figure indicates some variability in sensitivity among US-23 isolates collected from WI in previous years. Line at 10% indicates threshold for sensitivity category % indicates intermediate sensitivity to mefenoxam. Greater than 60% indicates resistance to mefenoxam. Free late blight diagnostics: In order to help better understand the epidemic at hand, please submit samples to my lab or work through your county agent and request that they send to me for genotyping. All we need to know is the county of sample origin. Identification of genotype at the county level would be very helpful in improving our understanding of this epidemic and potential future risks. Lab address is: Amanda Gevens, 1630 Linden Dr, Room 689, Plant Pathology Dept., University of Wisconsin, Madison, WI Please send infected leaves in a slightly inflated ziplock bag with no paper towel. Overnight shipping is best. For further symptom and management information, please visit the UW-Vegetable Pathology website for additional late blight photos and links to other late blight information and identification resources for organic, conventional, and home gardeners.