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Foliar Diseases of Tomato

There are several foliar diseases caused by fungal and bacterial pathogens that affect tomato routinely on Long Island, and elsewhere in the Northeast.  Photographs and information about these and other diseases of tomato, including management recommendations and occurrence, are in the Photo Gallery tomato section.  Research has been conducted at LIHREC to evaluate biopesticides and conventional fungicides for powdery mildew, Septoria leaf spot, bacterial speck, leaf mold, and timber rot (aka white mold).  Septoria leaf spot occurs commonly in organically-produced tomatoes on Long Island. Powdery mildew occurs more sporadically, but can become quite severe. Bacterial speck is the most common bacterial disease of tomato on Long Island. Leaf mold occurs less commonly in field-grown crops because the pathogen needs high humidity. There is a separate webpage with information about research conducted on late blight.  In most experiments diseases developed naturally; sometimes there was an inoculated spreader row. Experimental products are evaluated in terms of efficacy and product safety to the plant (e.g. phytotoxicity) to support their registration for specific diseases.  Registered products are also evaluated to be able to provide growers with research-supported management recommendations.

Plants are grown following standard procedure for fresh-market tomato production for the region. Usually they were transplanted into beds with drip irrigation and covered with black plastic mulch, and staked and trellised so plants are upright. Foliar applications were made using a CO2-pressurized backpack sprayer with a boom that has a single twin-jet nozzle with 110 degree output angle, and calibrated to deliver 45-50 gal/A when operated at 55 psi. Each side of the planted row was treated with the boom held sideways to obtain thorough coverage of foliage and to mimic the coverage obtained with a drop nozzle on a tractor sprayer. A 7-day application schedule was used.

Topics on this page:

Fungicide Evaluations – Conventional Products

2022: Bacterial speck was controlled with the conventional fungicide treatment (Badge X2 plus Manzate ProStick applied in alternation with Actigard, starting with Actigard, until about 2 weeks before first fruit expected to be ripe, then applied weekly) in a biopesticide evaluation.

2020: Bacterial speck was controlled in greenhouse seedlings with the conventional fungicide treatment (Mastercop plus Manzate Pro-Stick applied in alternation with Harbour) in a biopesticide evaluation.

2019: Bacterial speck incidence (percent leaves with symptoms) and severity were reduced by LifeGard applied in alternation with Kocide 3000-O plus Manzate Pro-Stick.  Control was not improved by applying Kocide plus Manzate every week.  Kocide plus Manzate applied every week without LifeGard was not effective.  A copper-sensitive bacterial isolate was used.  AgriPhage was ineffective.  The manufacturer (OmniLytics) determined that the phage strains in the formulation used had limited activity against the pathogen isolate used in the experiment, which would affect efficacy.

2014: Powdery mildew was effectively managed with Prolivo (tested as the experimental IKF-309) at both rates tested and also applied on a 14-day schedule. Applications were started the day after observing symptoms in all plots.  Prolivo is labeled for this use (as of 2023).

2012: Timber rot incidence (% plants with symptoms) was not significantly reduced with the fungicides tested.  Plants were inoculated by wounding and then spraying a spore solution.  Applications were started beforehand.

2011: Septoria leaf spot and powdery mildew were effectively managed with Mettle and Rally, but powdery mildew pressure was very low perhaps due to frequent rainfall.  Applications were started before observing symptoms.  These fungicides are labeled for powdery mildew; only Mettle is also labeled for Septoria leaf spot (as of 2023).

2010:  Powdery mildew, the focus of this experiment, was very effectively managed with Quadris Opti and 3 experimental fungicides from BASF Corp: BAS 560 is Vivando, its active ingredient plus another is in BAS 639, and BAS 9150 contains difenoconazole, an active ingredient in Aprovia Top, Inspire Super, and Quadris Top.  All 5 fungicides are labeled for this use.  No significant differences in incidence of leaves with symptoms of Septoria leaf spot were detected among treatments; however, occurrence of this disease in non-treated plots may have been limited due to leaf tissue already being affected by powdery mildew.  All fungicides listed above except Vivando are also labeled for this.  Development of both diseases was late with first symptoms seen in late August.

2001: Powdery mildew was effectively managed with Cabrio and Cabrio alternated with Bravo, but disease pressure was low.  Applications were started 5 days after observing symptoms in a spreader row.

2000: Powdery mildew was effectively managed with Flint, Quadris, and Cabrio (tested as the experimental BAS 500). Plants treated with Flint or Cabrio at 1 lb/A had statistically more fruit than plants in untreated control. Quadris and Cabrio are labeled for this use (as of 2023).

Publications listed below have more information about research results summarized above, including table with results.  To download report click on publication year, which is year after study was done; all are available at Plant Disease Management Reports website. Those for experiments with focus on biopesticides are in that section’s publication list.

  1. McGrath, M. T. and Downing, C. T.  2023.  Evaluation of biopesticides and copper for bacterial speck in tomato, 2022.  Plant Disease Management Reports 17:V064.
  2.  McGrath, M. T. and Yakaboski, A.  2021.  Efficacy of biopesticides for managing bacterial speck in tomato seedlings, 2020.  Plant Disease Management Reports 15:V064.
  3. McGrath, M. T. and Sexton, Z. F.  2020.  Efficacy of fungicides for managing bacterial speck in tomato, 2019.  Plant Disease Management Reports 14:V072.
  4. McGrath, M. T. and LaMarsh, K. A.  2015.  Evaluation of pyriofenone for powdery mildew in tomato, 2014.  Plant Disease Management Reports 9:V033.
  5. McGrath, M. T. and LaMarsh, K. A.  2013.  Evaluation of fungicides for controlling timber rot in tomato, 2012.  Plant Disease Management Reports 7:V022.
  6. McGrath, M. T., and Hunsberger, L. K.  2012. Evaluation of fungicides for powdery mildew in tomato, 2011. Plant Disease Management Reports 6:V081.
  7. McGrath, M. T., and Hunsberger, L. K.  2011.  Evaluation of BASF experimental fungicides for powdery mildew in tomato, 2010.  Plant Disease Management Reports 5:V102.
  8. Shishkoff, N., and McGrath, M. T.  2002.  Evaluation of fungicides for powdery mildew in staked tomatoes, 2001.  Fungicide and Nematicide Tests 57:V119.
  9. Shishkoff, N., and McGrath, M. T. 2001. Evaluation of fungicides for powdery mildew in staked tomatoes, 2000.  Fungicide and Nematicide Tests 2001:V109.

Fungicide Evaluations – Biopesticides and other Organic Products

Products tested, year tested, and diseases that occurred.

Disease/Product 2022 2020 2019 2014 2013 2012 2011 2009 2008 2006 2005 2004 2003
Bacterial speck X X X X X
Late blight X X X
Leaf mold X
Powdery mildew X X X X X X X
Septoria leaf spot X X X X X X X X
Biopesticides and other organic, non-copper fungicides
Actinovate AG X X X
AgriPhage X
Companion X X
Double Nickel X X
JMS Stylet-oil X
LifeGard X X
MilStop X X X
Organocide X X
Regalia SC X X X X X
Saf-T-Cide X X
Serifel X
Optiva (=Serenade ASO) X
Serenade ASO X X
Serenade Soil X X X
Sonata ASO X X X X
Sporatec AG X X
Stargus X
Taegro X X
TerraGrow 2 X
Timorex ACT X
Timorex Gold X X
Experimental biopesticides
AgriLife (citrus acid) X X
CranProtect X
Zinkicide X
Copper fungicides
Badge X2 X X X X
Basic Copper 53 WP X
Champion WP X X
Cueva X X X
Kocide 3000 X X
Kocide 3000-O X
Mastercop X
Nordox 75WG X X X

2022: Bacterial speck incidence (percent leaves with symptoms) at most ratings was numerical but not significantly lower with Cueva (organic copper fungicide) and the biopesticides tested on a weekly application schedule: Serifel, Timorex ACT, and LifeGard applied in alternation with Cueva. Based on AUDPC values, control was achieved only with the conventional fungicide treatment (Badge X2 plus Manzate Pro-Stick applied in alternation with Actigard until about 2 weeks before first fruit expected to be ripe, then applied weekly).  A copper-sensitive bacterial isolate was used.  Disease onset was earlier than planned likely due to pathogen spread in the greenhouse from inoculated seedlings for a spreader row to the experiment seedlings although the 2 group were 38 ft apart.  Symptoms were seen at the second application (19 days after transplanting) which was intended to be preventive.  Rain created conditions favorable for pathogen spread and speck development during June and September.  For photographs of the experiment see: Evaluation of Organic Biopesticides for Tomato Bacterial Speck, 2022

2020: Bacterial speck was suppressed based on severity ratings by the one treatment with registered biopesticides (Regalia applied in alternation with TerraGrow and with Stargus; Regalia is labeled for speck; TerraGrow is a microbial inoculant, not a fungicide). 2 of the 6 experimental biopesticides tested were similarly effective. The conventional fungicide treatment was the most effective.

2019: Bacterial speck was successfully established and maintained in the experiment, but disease pressure was affected by environmental conditions and combined with plant growth resulted in fluctuations in incidence and severity week to week. The 2 treatments with LifeGard were significantly reducing disease severity and incidence compared to the untreated control during weeks when disease pressure was highest. They were LifeGard applied every 14 days with Kocide 3000-O plus Manzate Pro-Stick applied weekly or in alternation with LifeGard. Kocide 3000-O plus Manzate Pro-Stick applied weekly was ineffective. AgriPhage was also ineffective. The manufacturer (OmniLytics) determined that the phage strains in the formulation used had limited activity against the pathogen isolate used in the experiment, which would affect efficacy.. There were 2 inoculated spreader rows between treatment rows to provide a source of the pathogen.

2014: Four organic copper fungicides were compared in terms of ability to control foliar disease and amount of residue. Diseases developed naturally. Late blight was initially controlled with conventional fungicides due to concern of spread to other experiments if the copper fungicides were not adequately effective.  Powdery mildew was the main disease. All copper fungicides provided similar control based on the assessment on 7 Oct. Cueva and Basic Copper 53 were most effective based on AUDPC values. There were no significant differences in severity of bacterial speck or late blight, but severity of both were low, or defoliation.  Copper fungicide residue was more visible on fruit of plants treated with Basic Copper 53 than the others. There were no significant differences among the other products. Amount of residue was numerically lowest for Nordox 75WG, which is red.

2013: During the growing season, as rainfall decreased, conditions became progressively less favorable for development of most foliar diseases until late summer. Symptoms were first observed of Septoria leaf spot on 7 Aug, of late blight on 28 Aug, and of powdery mildew on 3 Sep. Foliar applications were made from 16 Aug – 24 Sep. A late blight resistant variety was used because the focus was other diseases; few symptoms were seen. No significant differences were detected among treatments in amount of leaves affected for any of the diseases, but AUDPC values were always greatest for the nontreated control, however, they were least for the conventional fungicide treatment (Bravo Ultrex), and the next best treatment numerically was a copper fungicide used as the organic standard (Cueva). Biopesticide treatments also ranked similarly for AUDPC values for Septoria leaf spot and powdery mildew. 3 treatments with an experimental had the lowest values (least disease), Actinovate + the copper fungicide Badge X2 was next, then Actinovate, Regalia alternated with Cueva, Regalia + Cueva, MilStop + Optiva (active ingredient marketed as Serenade ASO subsequently), Double Nickel + Cueva, Optiva alternated with Cueva, and Optiva.

2012:  Tomato plants did not grow well perhaps because the fertilizer used did not provide adequate nutrients and/or the ryegrass living mulch was able to utilize fertilizer placed under the plastic mulch. This likely affected disease development. Both Septoria leaf spot and powdery mildew have been severe in other experiments in this location. No differences were detected among treatments.

2011:  Environmental conditions were atypical for the region during late Aug and Sep with a hurricane plus rain occurring on many more days than usual. Rain provided favorable conditions for disease development, especially Septoria leaf spot (splashing water disperses pathogen spores and wet leaf tissue is favorable for infection), but not for applying fungicide treatments or for plant growth. Research plants were damaged by the strong winds and intensive rainfall occurring during the storms, especially during Hurricane Irene on 28 Aug. The main damage was defoliation. Rain fell on 10 days during Aug, delivering a total of 10.6 inches. Another major rainfall of 3.4 inches occurred over 6-8 Sep. Symptoms of Septoria leaf spot were first observed on 24 Aug, and powdery mildew on 12 Sep. No significant differences were detected among treatments. None of the treatments provided significant suppression of either disease that developed, including Bravo (active ingredient is chlorothalonil), the conventional fungicide included as a check primarily for assessing application timing. These results with Bravo provide support for the conclusions that environmental conditions impacted the success of this experiment. Severity of powdery mildew on 27 Sep was numerically lower than the non-treated control for all treatments. The value was lowest for MilStop. Bravo was next lowest, then Timorex Gold (subsequently replaced by Timorex ACT). Severity of Septoria leaf spot on 27 Sep was numerically lower than the non-treated control for plants treated with Bravo, Sonata alternated with the copper fungicide Nordox, and Nordox alone.

2009:  Septoria leaf spot was the main disease. Symptoms were first observed on 3 Aug when plants were trellised and first immature fruit were present. Powdery mildew developed later and remained at a low level. Conditions were favorable for Septoria leaf spot. Symptoms became more severe in all treatments, including the conventional fungicide standard, than in a similar experiment conducted in 2008. Based on canopy severity on 29 Sep, the conventional fungicide standard was providing 77% control. Despite the high disease pressure, three treatments controlled Septoria leaf spot as effectively as the conventional standard: Organocide (at low label rate) alternated with Kocide 3000, Actinovate alternated with Kocide, and Taegro alternated with Kocide (63-79%). All four fungicides were ineffective used alone. Other biopesticides tested that were ineffective: Regalia SC, Companion, and Sporatec (subsequently replaced by Sporan). Treatments providing the best control of Septoria leaf spot generally had the highest yields; however, the means did not always differ significantly from the nontreated control.

2008:  Conditions were not ideal for tomato production in 2008 with several severe rainstorms that included hail and strong winds as well as heavy rain. Diseases developed naturally. Symptoms were not seen until 9 Sep when first ripe fruit were seen. The third or fourth application was made for each of the biopesticide treatments on 10 Sep. Dates of first observations were 10 Sep for powdery mildew, 15 Sep for Septoria leaf spot and 3 Oct for late blight. All treatments provided some suppression of powdery mildew based on the incidence assessment on 6 Oct. Septoria leaf spot was suppressed by all treatments except Taegro and Sporatec AG (subsequently replaced by Sporan). Degree of control was not as high as that obtained for powdery mildew, even with the standard organic fungicide (the copper Kocide 3000) and with the conventional fungicide program (Actigard alternated with Kocide 3000 + Dithane and Flint included twice). Incidence and severity of Septoria leaf spot was numerically higher than for powdery mildew on nontreated plants for most assessments. Actinovate SP was moderately effective for powdery mildew and for Septoria leaf spot. Companion provided control of both powdery mildew and Septoria leaf spot. Regalia SC (tested as the experimental MOI-106) provided excellent suppression of powdery mildew (91 to 99%). Septoria leaf spot was also suppressed based on most assessments. Based on the 6 Oct assessments, level of control was significantly better when Regalia was applied in alternation with Kocide 3000 rather than used every week: 59% versus 20% control for severity and 84% versus 50% for incidence. Organocide provided good control of Septoria leaf spot based on incidence data (47 to 62%) and excellent control of powdery mildew (79 to 97%). Control was improved, sometimes significantly, when Organocide was applied at half the rate tank-mixed with Kocide 3000 at the lowest labeled rate. Sporatec applied with the adjuvant BioLink controlled powdery mildew but not Septoria leaf spot. Degree of control of powdery mildew ranged from 61 to 88%. However, excellent control of both diseases was obtained when Sporatec was applied with Saf-T-Side: 65 to 91% for Septoria and 91 to 100% for powdery mildew. Degree of control was not significantly different from the organic standard. Taegro exhibited some suppression of powdery mildew based on the 6 Oct incidence data. It was ineffective for Septoria leaf spot.

2006:  The objective of this study was to evaluate applications of AgriLife (2 rates) and an OMRI-approved copper fungicide (Champion) for control of foliar diseases of tomato. AgriLife used in this experiment is a citrus acid product that reportedly promotes plant health. It was discontinued. There is a copper fungicide called Agri-Life registered in the U.S. in 2020.  AgriLife was applied to the ground early in plant growth as well as to foliage throughout the growing season.  Powdery mildew and Septoria leaf spot were first observed in the field on 13 Sep. All 3 treatments were ineffective on all assessment dates for Septoria leaf spot. All were equally effective for powdery mildew on upper leaf surfaces based on AUDPC values. AgriLife (1:50) and Champion WP (2 lb/A) were the most effective treatments for powdery mildew on lower leaf surfaces; AgriLife (1:100) provided significantly less control but still reduced disease compared to the control based on AUDPC values. Plants treated with AgriLife (1:50) yielded significantly less based on fruit weight than the other treatments suggesting this dose applied throughout the growing season was too high. There were not significant differences among treatments in total number of fruit per plant.

2005:  The objective of this study was to evaluate hairy vetch plus rye mulch used alone or combined with applications of AgriLife for control of foliar diseases of tomato by comparing these treatments to tomatoes grown in bare ground (rototilled). See paragraph above for information about AgriLife. As in that study, AgriLife was applied to the ground early in plant growth as well as to foliage throughout the growing season. Leaf mold developed naturally and was first observed in the field on 6 Sep. Neither leaf mold incidence nor severity were lower for tomato grown in hairy vetch mulch than tomato grown in bare ground. Hairy vetch mulch has suppressed disease in other experiments and been shown to activate defense genes in tomato. In the current experiment there may not have been sufficient hairy vetch biomass since it was grown with rye. Vetch plus rye is a commonly used combination cover crop. Tomato plants treated with AgriLife had numerically lowest disease ratings at all assessments with incidence on 27 Sep being significantly lower than the vetch mulch or bare ground treatments. There were no significant differences in yield among treatments.

2003 and 2004:  Main objective was to evaluate compost tea used alone, with a microbial biopesticide (Sonata which was one of few marketed then), or with organic fungicides applied after symptoms seen as ‘rescue’ treatments (2004 experiment; JMS Stylet Oil for powdery mildew and a copper fungicide). Compost tea was examined because organic growers were interested in knowing its efficacy, and documented efficacy could support development of a commercial product. Applying a compost tea produced on farm to manage a disease in crops that will be sold is an illegal pesticide application in the U.S. The linked reports have information about how the compost tea was produced and tested.  Plants were grown using organic production practices in a field at LIHREC dedicated to organic research.

2004:  Powdery mildew was first observed on 20 Aug. Septoria leaf spot and bacterial speck were seen on 1 Sep. No significant differences were detected among treatments in disease severity or yield. Thus, additional nitrogen fertilizer did not increase yield and the foliar disease control treatments were ineffective for the diseases that occurred. Based on the analysis of tea prepared on 9 Sep, fungal activity was low (0.91 and 0.45 ppm for tea from brewer and nozzle, respectively) while active bacterial biomass was in a good range (16 and 54.4 ppm, respectively), thus the tea is considered bacterial with good fungal biomass. The leaf-based compost had very high fungal activity before the experiment was started (99.8 ppm on 28 April); it was only 36.8 ppm on 8 Sep. Active bacterial biomass increased from 47.8 ppm in April to 69.4 ppm in Sep. The leaf organism assay revealed that leaf coverage with bacteria and fungi was inadequate on leaves collected immediately before tea application. Leaves collected about 1 hour after tea was applied were 76% covered by bacteria and 17% covered by fungi, which is considered very good. A tea with more fungal activity may be needed to suppress fungal diseases. Effective control with compost tea may necessitate modifying application timing, such as applying late in the day and/or starting earlier in crop development, perhaps including a seed treatment.

2003:  Symptoms of powdery mildew were first observed in one plot on 3 Sep. Septoria leaf spot was seen on 8 Sep. These diseases became widespread in the field by 22 Sep causing severely affected leaves to die. Leaf mold was also seen; incidence was too low to rate. No significant differences were detected among treatments; however, disease severity was numerically lowest where Sonata and compost tea were applied. Based on the organismal analysis conducted by Soil Foodweb NY, the compost tea used in this experiment was primarily bacterial, although the ingredients used were anticipated to produce a fungal-dominant tea. Both active and total bacterial biomass were high (33.8 and 576 ppm). Bacterial biomass was higher for the compost tea sample from the nozzle, likely reflecting that Nu-Film-P can be a food source for bacteria. Active and total fungal biomass was only 1.28 and 1.73 ppm, respectively. A compost tea with more fungal activity may be needed to suppress fungal diseases of tomato. Additionally, the organisms in compost tea may be better able to establish on leaves when applied before night rather than in the morning. First fruit were noted on 25 July. At that time, high nitrogen plants, those that had received peanut meal, were observed to be larger and greener than those that had not. Compost tea treatments did not have a detectable impact on plant appearance. High nitrogen plants produced numerically more marketable fruit (at least 2.5 inch in diameter) than those that did not (13 vs 10 per plant), but this difference was not statistically significant.

 

Publications listed below have more information about research results summarized above, including table with results.  Click on publication year to download report; all are available at Plant Disease Management Reports website.

  1. McGrath, M. T. and Downing, C. T.  2023.  Evaluation of biopesticides and copper for bacterial speck in tomato, 2022.  Plant Disease Management Reports 17:V064.
  2.  McGrath, M. T. and Yakaboski, A.  2021.  Efficacy of biopesticides for managing bacterial speck in tomato seedlings, 2020.  Plant Disease Management Reports 15:V064.
  3. McGrath, M. T. and Sexton, Z. F.  2020.  Efficacy of fungicides for managing bacterial speck in tomato, 2019.  Plant Disease Management Reports 14:V072.
  4. McGrath, M. T. and LaMarsh, K. A.  2015.  Comparison of organic copper fungicides for foliar diseases in tomato, 2014.  Plant Disease Management Reports 9:V025.
  5. McGrath, M. T. and LaMarsh, K. A.  2014.  Evaluation of biopesticides for foliar diseases in organically-produced tomato, 2013.  Plant Disease Management Reports 8:V194.
  6. McGrath, M. T. and LaMarsh, K. A.  2013.  Evaluation of biopesticides for managing foliar diseases in organically-produced tomato, 2012.  Plant Disease Management Reports 7:V106.
  7. McGrath, M. T., and Hunsberger, L. K.  2012. Evaluation of biopesticides for foliar diseases in organically-produced tomato, 2011. Plant Disease Management Reports 6:V100.
  8.  McGrath, M. T., and Fox, G. M. 2010. Efficacy of biopesticides for managing foliar diseases in organically-produced tomato, 2009.  Plant Disease Management Reports 4:V115.
  9. McGrath, M. T., and Fox, G. M. 2009. Efficacy of biopesticides for managing foliar diseases in organically-produced tomato, 2008.  Plant Disease Management Reports 3:V127.
  10. McGrath, M. T., and Davey, J. F. 2007. Evaluation of a health-promoting product and a copper fungicide on foliar diseases in organically-produced tomato, 2006. Plant Disease Management Reports 1:V147.
  11. McGrath, M. T., and Davey, J. F. 2006. Evaluation of hairy vetch plus rye mulch and a health-promoting product on leaf mold in organically-produced tomato, 2005. Fungicide and Nematicide Tests 61:V024.
  12. McGrath, M. T., and Moyer, D. D.  2005. Evaluation of compost tea and biofungicide Sonata for foliar diseases in organically produced tomatoes, 2004. Fungicide and Nematicide Tests 60:V052.
  13. McGrath, M. T., and Moyer, D. D.  2004. Evaluation of compost tea and biofungicide Sonata for foliar diseases in organically produced tomatoes, 2003. Fungicide and Nematicide Tests 59:V053.