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Basil Downy Mildew

Research Topics, Results and Reports

Replicated experiments have been conducted since 2010 under field conditions at the Cornell University research facility on Long Island. Plots were single beds with one or two staggered rows of basil at 9-inch plant spacing. Naturally-occurring inoculum was relied on. Fungicides were applied with a backpack sprayer beginning before or after symptoms were found in the field, which included basil planted before the experiments to serve as a spreader row. A boom with a single (TJ60-4004EVS) nozzle delivering spray to the top of plants was used in 2010 and 2011. Starting in 2012, this boom was used for the first applications until basil plants were large enough to use a boom with two drop nozzles directed to the side of plants as well as a nozzle delivering spray over the top of the plant. This boom was used to improve coverage achieved with a single nozzle directed to the top of plants. Most fungicide treatments were applied on a weekly schedule. Percent affected leaves (with sporulation of the pathogen visible on the underside) was assessed rather than severity (except in 2010) because any amount of symptoms renders a leaf unmarketable.

Fungicide Evaluations – Conventional Products – When tested singly, the most effective fungicides in the 2013 experiment were Zampro*, Revus, Orondis (pka Zorvec)*, and Ranman (*not registered yet). ProPhyt was effective in 2013 but not 2012 when another phosphorous acid fungicide, K-Phite, also was ineffective. Presidio was ineffective. Only Orondis and Zampro were effective in the 2012 experiment. Revus was ineffective in 2010 and 2011 when a single-nozzle boom was used. Limited efficacy detected in these experiments is at least partly due to the stringent assessment used: when assessing percent leaves affected, the severity of disease on the leaves is not taken into considered in the assessment. Best control (90-100%) was obtained with combination programs that were applied on a preventive, weekly schedule using a boom with drop nozzles in 2014 and also 2015 (2015a report). The programs included Ridomil, Quadris, Ranman, Revus, and K-Phite or Quadris, Ranman, Revus, and Orondis. K-Phite was applied at lowest label rate with all applications of the other fungicides based on the current opinion that this is the best use pattern for phosphorous acid fungicides. Many of these fungicides in different combinations in another experiment provided poor control at least partly due to an unintended lapse in the spray schedule with 13 days between applications and rainfall 9 days after the previous application (2015b report). Excellent control was obtained with 4 fungicide programs with Orondis, Revus, and Prophyt indicating this combination of chemistry was more important than specific timing for each fungicide (2016 report).  Ranman applied in alternation with Revus + K-Phite was not quite as effective (89% vs 99% control).

2016 2015a | 2015b | 2014 | 2013 | 2012 | 2011 | 2010

View article in the journal Plant Disease on this work.

Fungicide Evaluations – Organic Products – Products evaluated singly were Actinovate, BioGuard*, Companion*, Organocide*, Oxidate, Procidic, Regalia, Sporatec*, Sonata*, and Timorex Gold* (*product not registered or not labeled for this use).  All provided little to no control based on percentage of leaves with symptoms, which is a rigorous assessment measure, but realistic reflecting the level of control needed to produce a marketable crop. All products tested singly were applied on a preventive, 7-day schedule with the exception of OxiDate, which was applied twice weekly in 2011. Applications were made with a single nozzle boom over the top of plants in 2010 and 2011, when the focus of evaluations was on products approved for organic production and other biopesticides. However, control of downy mildew was not achieved with the organic products tested singly in 2012 and the combination programs tested in 2013, 2014, and 2015, which were all applied with a boom with three nozzles per plant, two of which were drops. The combination program consisted of Regalia applied to soil starting at transplanting followed by Actinovate alternated with Trilogy applied to foliage in 2013 and 2014 or MilStop + Double Nickel alternated with Regalia + Double Nickel + Cueva and then Trilogy applied to foliage in 2015. The foliage sprays were made approximately twice weekly in 2014 and 2015 (2015a report), and started at least 24 days before symptoms were found in the experiment. These combination programs were also tested on a moderately resistant variety, Eleonora; but using this integrated program (fungicides applied to a resistant variety) also did not result in successful control. No treatments were effective in another experiment with organic products (Double Nickel, Double Nickel + Regalia, Procidic, and Sil-Matrix) and a non-organic biopesticide (Oso) all applied in alternation with a copper fungicide, Cueva (2015c report).  Cueva was effective in the 2016 experiment based on defoliation ratings.  Procidic was not effective in this field experiment but was in a greenhouse experiment with plants dipped in fungicide solution to examine efficacy without inadequate spray coverage being a confounding factor. Acknowledgment: this research was mostly funded by the IR-4 Project, Biopesticide and Organic Support Program

20162015a | 2015c | 2014 | 2013 | 2012 | 2011 | 2010

Plant Resistance Evaluations – Breeding Lines and Experimental Varieties–Excellent suppression of downy mildew was achieved in 2013 and 2014 with some resistant experimental varieties developed at Rutgers. They performed at least as well as resistant breeding lines and inherently resistant spice basil types. No symptoms were observed on some in 2014. A commercial resistant variety, Eleonora, exhibited some suppression.  Experimental varieties from Enza Zaden USA, Inc. and PanAmerican Seed performed better than Eleonora in 2015.  M4828Z has been commercialized and named Everleaf Genovese and Pesto Party (marketing name for Burpee).  In 2018 degree of control of downy mildew provided by four resistant varieties developed at Rutgers and being marketed by VanDrunen Specialty Seeds was 48% for Obsession, 64% for Devotion, 80% for Passion, and 81% for Thunderstruck, based on AUDPC values compared with Martina.  No symptoms or signs of downy mildew were found on any plants of Amazel (Proven Winners) or Prospera (Genesis Seeds).  Cultivar ranking based on average rating from 12 growers was Amazel (9.1 for appearance, 6.3 for taste, 8.6 for marketability), Passion (7.6, 6.8, 7.6), Prospera (7.5, 6.5, 6.6), Obsession (6.8, 6.2, 6.6), and Thunderstruck (5.9, 6.4, 5.2). All ratings and comments.

2018 2018 Photos2015d | 2014a | 2014b | 2013a | 2013b

Results from Monitoring Program started in 2009

First observations of basil and cucumber downy mildews at LIHREC.

Onset of downy mildew development at LIHREC is very regular, with first symptoms found between 4 and 19 August since 2009; in contrast, first symptoms of downy mildew were found in cucumber from 17 July to 7 September over the years.


Basil Cucumber
2009 5 Aug 27 Jul
2010 10 Aug 7 Sep
2011 19 Aug 1 Aug
2012 16 Aug 17 Jul
2013 6 Aug 22 Jul
2014 18 Aug 2 Sep
2015 10 Aug 10 Aug
2016 15 Aug 8 Aug
2017 4 Aug 31 Jul
2018 7 Aug 14 Aug
2019 16 Aug 19 Aug
2020 17 Aug 17 Aug

Extension presentations

  • Downy  Mildews  of Basil,  Spinach, &  Other  Crops handout and presentation at PASA Conference Feb 2018
  • Field Studies on Managing Basil Downy Mildew in New York.  Proceedings and presentation at 2019 New Jersey Agricultural Convention and Trade Show Feb 2019

Research presentations

Photo gallery

Extension articles and meeting proceedings


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