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Organic disease management: Powdery mildew in cucurbit crops

Evaluations of Biopesticides and other Organic Fungicides

Replicated experiments conducted under field conditions at the Cornell University research facility on Long Island have mostly been evaluations of products approved for or in development for organic production.

Applications were started after finding symptoms (IPM threshold is 1 affected out of 50 older leaves examined) and made on a weekly schedule using a tractor-sprayer to a susceptible pumpkin variety, except where noted otherwise.  Powdery mildew severity was assessed weekly on upper and lower leaf surfaces.  Achieving control on lower leaf surfaces (underside) is challenging with contact organic fungicides because of the difficulty of delivering spray material there, especially in pumpkin and other larger-leaved cucurbit crop types.  Powdery mildew develops best on the lower leaf surface and its development there will cause leaves to die prematurely, albeit not as quickly as when no fungicides are applied. Some products tested were not an organic formulation. Others are not available.  For more details about the procedures and results, including data table, see report pdf files linked below in reference section by year of report publication (plus letter when multiple reports in same year), which is one year after experiment conducted.

Products evaluated singly:

Applied alone each time. Rate is per acre unless specified otherwise. Year is when published in list of reports below.

  • Actinovate 6 oz effective on upper surface only (2007).
  • Armicarb 100 4 lb was effective on upper surface and slightly on lower (2002c).
  • Copper (Badge X2, Basic Copper 53, Nordox, and NuCop HB) provided good control in zucchini on upper leaf surfaces, ineffective on lower; no significant differences. Another product, Cueva, was ineffective at 2 qt/A (2014).
  • JMS Stylet-oil 5 qt/100 gal very effective on upper leaf surface, some to good efficacy on lower (2002c, 2004b, 2005a when applied with compost tea which alone was ineffective). Moderately effective on upper surfaces (2003, 2006).
  • Kaligreen 4-5 lb moderate to good efficacy on upper surfaces (2003, 2002c).
  • LifeGard 4.5 oz/100 gal somewhat effective on upper leaf surfaces; preventive schedule. Resistant acorn squash variety used (2019c).
  • Microthiol Disperss 80W 4-5 lb/A very effective on upper leaf surfaces, numerically best organic product (JMS Stylet-oil equally effective in 2002c); variable efficacy on lower: none (2003), some (2005b, 2006), good (2002c). At least 50% control on both surfaces (2007). Very effective on upper surface, some control on lower (not in 2016); slightly better than Tritek (2017b, 2018, 2019a; last conducted with winter squash).
  • Mildew Cure 1% (was named GC-3 organic fungicide) very effective on upper leaf surfaces, some efficacy on lower (2005b).  Ineffective; provided some control early in disease development based on assessment after 2 applications when severity low (2006).  Effective on upper surface only (2007).
  • Milstop 2.5-3 lb/A effective on upper but not lower surface (2007). Ineffective on both leaf surfaces in pumpkin (2008c) and cantaloupe (2008b) but effective on upper in butternut squash (2008a); when experiment repeated, effective on both leaf surfaces in cantaloupe (2010b), effective only on upper in butternut squash (2010a).
  • Organocide 2 fl oz/gal very effective on upper leaf surfaces, some efficacy on lower (2005b).  Effective on upper surfaces, provided some control on lower surface early in disease development based on rating after 2 applications when severity low (2006). Effective only on upper surface in pumpkin (2008c) and in butternut squash (2008a) but ineffective in cantaloupe (2008b); when experiment repeated, effective on both leaf surfaces in cantaloupe (2010b) and in butternut squash (2010a). Organocide more effective than Milstop in one experiment (2008a).
  • Oso pre-cursor (Polyoxin 2.5% 28 and 71 oz) effective on upper surface and slightly on lower leaf surface (2008d).
  • OxiDate 128 fl oz/100 gal ineffective applied following the IPM or a curative schedule starting with three consecutive applications when powdery mildew reached a level of being easily seen but not severe (average severity on older leaves was 1% on upper surfaces and 2% on lower surfaces). IPM treatment provided some control early in disease development based on assessment after 3 applications when severity low (2005b). Similar results with applications twice weekly (2006).
  • Proud-3 4 qt/A (thyme oil) effective on upper surface only (2007). Not available in several states including NY (2019).
  • Regalia pre-cursor (Milsana) 1% effective on upper surface, not on lower (2002c).
  • Regalia pre-cursor (MOI-106) 1% somewhat effective on upper surface, provided limited control on lower surface early in disease development based on rating after 4 applications when severity moderately low (2009).
  • Serenade AS 6 lb ineffective (2003) to moderately effective on upper surfaces (2002c).
  • Serenade 1 gal/A effective on upper surfaces, applied with compost tea, which was ineffective applied alone (2004, 2005a).  Also effective on lower surfaces (2005a).
  • Serenade Opti 20 oz/A ineffective (2017a).
  • Sonata 2 qt/A ineffective applied alone (2004, 2005a), effective combined with compost tea (which was ineffective applied alone) on lower leaf surface (2004) and both leaf surfaces (2005a).
  • Sporan (aka Sporatec) 1.5 qt/A + NuFilm P ineffective. Provided some control early in disease development based on assessment after 3 or 2 applications when severity low (2005b, 2006).
  • Trilogy 1% moderately effective on upper leaf surfaces, no efficacy on lower (2004) or limited efficacy (2006).
  • Tritek 2% v/v very effective on upper surface but not as effective as Microthiol Disperss, some control on lower (2017b, 2018, 2019a; last conducted with winter squash).

Programs with multiple products evaluated:

  • Microthiol Sulfur (4 lb/A) followed by Armicarb (4 lb/A) alt copper (not organic formulation) effective on upper leaf surfaces of susceptible and resistant varieties of pumpkin (2001b) and cantaloupe (2001a) and also lower surface of susceptible cantaloupe.
  • Microthiol Sulfur (4 lb/A) followed by copper alt Kaligreen (4 lb/A) effective on upper leaf surfaces of susceptible and resistant varieties of pumpkin (2002b) and cantaloupe (2002a) and also lower surface of pumpkin and resistant cantaloupe.
  • Cueva 2 qt/A + Double Nickel 2 lb/A alt. Timorex Gold 0.6 fl oz/gal (4,6) somewhat effective on upper leaf surfaces; efficacy not improved by applying LifeGard 4.5 oz/100 gal weekly starting 2 wks before symptoms seen. Resistant acorn squash variety used (2019c).
  • LifeGard 4.5 oz/100 gal (twice before symptoms) then Milstop 3 lbs/A alt Serifel 8 oz/A alt Suffoil-X 1% v/v appeared to be effective until the last assessment. Data nor analyzed due to loss of 2/4 plots. Other treatments tested consisted of biopesticide + conventional fungicides. Resistant acorn squash variety used (2019b).

Products evaluated that are not commercially available:

  • AgriLife 0.5% moderately effective on upper leaf surfaces, provided some control on lower surface early in disease development based on assessment after 2 applications when severity low (2006). AgriLife 3% effective on both surfaces (2007).
  • Eco E-Rase 1% (jojoba oil) very effective on upper leaf surfaces, some efficacy on lower especially in 2006 (2005b, 2006, 2007).
  • Genica BP 300 2.27% effective on upper surface only (2007, 2008d).

Reports with results listed above

  • McGrath, M. T.  2001a.  Alternative fungicides to Bravo evaluated on muskmelon cultivars differing in susceptibility to powdery mildew, 2000.  Fungicide and Nematicide Tests 2001:V75.
  • McGrath, M. T.  2001b.  Alternative fungicides to Bravo evaluated on pumpkin cultivars differing in susceptibility to powdery mildew, 2000.  Fungicide and Nematicide Tests 56:V77.
  • McGrath, M. T.  2002a.  Alternative fungicides to Bravo evaluated on muskmelon cultivars differing in susceptibility to powdery mildew, 2001.  Fungicide and Nematicide Tests 57:V48.
  • McGrath, M. T.  2002b. Alternative fungicides to Bravo evaluated on pumpkin cultivars differing in susceptibility to powdery mildew, 2001.  Fungicide and Nematicide Tests 57:V84.
  • McGrath, M. T.  2002c.  Evaluation of fungicide programs for managing powdery mildew of pumpkin, 2001.  Fungicide and Nematicide Tests 57:V86.
  • McGrath, M. T.  2003. Protectant fungicides for managing powdery mildew of pumpkin, 2002. Fungicide and Nematicide Tests 58:V022.
  • McGrath, M. T.  2004. Evaluation of biofungicides and compost tea for managing powdery mildew of pumpkin, 2003. Fungicide and Nematicide Tests 59:V055.
  • McGrath, M. T.  2005a. Evaluation of biofungicides used with compost tea for managing powdery mildew of pumpkin, 2004, Fungicide and Nematicide Tests 60:V050.
  • McGrath, M. T.  2005b. Evaluation of biofungicides for managing powdery mildew of pumpkin, 2004. Fungicide and Nematicide Tests 60:V051.
  • McGrath, M. T., and Davey, J. F. 2006. Evaluation of biofungicides for managing powdery mildew of pumpkin, 2005. Fungicide and Nematicide Tests 61:V036.
  • McGrath, M. T., and Davey, J. F. 2007. Evaluation of biofungicides for managing powdery mildew of pumpkin, 2006. Plant Disease Management Reports 1:V145.
  • McGrath, M. T., and Fox, G. M. 2008a.  Evaluation of integrated management programs with biofungicides and a resistant cultivar for managing powdery mildew in butternut squash, 2007. Plant Disease Management Reports 2:V079.
  • McGrath, M. T., and Fox, G. M. 2008b.  Evaluation of integrated management programs with biofungicides and a resistant cultivar for managing powdery mildew in muskmelon, 2007. Plant Disease Management Reports 2:V078.
  • McGrath, M. T., and Fox, G. M. 2008c.  Evaluation of integrated management programs with biofungicides and a resistant cultivar for managing powdery mildew in pumpkin, 2007. Plant Disease Management Reports 2:V141.
  • McGrath, M. T., and Fox, G. M. 2008d.  Evaluation of fungicides for managing powdery mildew in pumpkin, 2007. Plant Disease Management Reports 2:V142.
  • McGrath, M. T., and Fox, G. M. 2009. Evaluation of a biopesticide (MOI-106) and Rally for managing powdery mildew on pumpkin, 2008.  Plant Disease Management Reports 3:V124.
  • McGrath, M. T., and Fox, G. M. 2010a. Integrated programs with biopesticides and a resistant cultivar evaluated for powdery mildew in butternut squash, 2009.  Plant Disease Management Reports 4:V024.
  • McGrath, M. T., and Fox, G. M. 2010b. Integrated programs with biopesticides and a resistant cultivar evaluated for powdery mildew in muskmelon, 2009.  Plant Disease Management Reports 4:V025.
  • McGrath, M. T., and Fox, G. M. 2010c. Integrated programs with biopesticides and a resistant cultivar evaluated for powdery mildew in pumpkin, 2009. Plant Disease Management Reports 4:V114.
  • McGrath, M. T. and LaMarsh, K. A. 2014.  Comparison of organic and conventional copper fungicides for powdery mildew in zucchini, 2013. Plant Disease Management Reports 8:V193.
  • McGrath, M. T. and Sexton, Z. F.  2017a.  Efficacy of biopesticides for managing powdery mildew in pumpkin, 2016.  Plant Disease Management Reports 11:V025.
  • McGrath, M. T. and Sexton, Z. F.  2017b.  Evaluation of management programs without chlorothalonil for powdery mildew in pumpkin, 2016.  Plant Disease Management Reports 11:V026.
  • McGrath, M. T. and Sexton, Z. F.  2018. Evaluation of fungicides to reduce chlorothalonil use for powdery mildew on pumpkins, 2017.  Plant Disease Management Reports 12:V073.
  • McGrath, M. T. and Sexton, Z. F.  2019a.  Evaluation of fungicides to reduce chlorothalonil use for powdery mildew on squash, 2018.  Plant Disease Management Reports 13:V122.
  • McGrath, M. T. and Sexton, Z. F.  2019b.  Efficacy for powdery mildew on acorn squash of conventional and organic fungicide programs with biopesticides that induce systemic resistance, 2018.  Plant Disease Management Reports 13:V120.
  • McGrath, M. T. and Sexton, Z. F.  2019c.  Efficacy of organic fungicides for managing powdery mildew on acorn squash, 2018.  Plant Disease Management Reports 13:V121.

Acknowledgment: this research was mostly funded by the IR-4 Project, Biopesticide and Organic Support Program

 

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