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Cucurbit Powdery Mildew

This foliar, fungal disease is common wherever cucurbits are grown, including in the northeastern U.S.  This is because the pathogen produces an abundance of asexual spores (the powdery growth) easily dispersed by wind, thus it can spread widely, and the pathogen can produce a sexual spore in fall that enables it to survive over winter.  It is arguably the most important disease of cucurbits.

Effectively managing powdery mildew is essential for producing a high-quality cucurbit crop.  Leaves affected by powdery mildew die prematurely which results in fewer fruit and/or fruit of low quality (poor flavor, sunscald, poor storability).  Powdery mildew is managed with resistant varieties and fungicides.  Avoiding the pathogen or creating less favorable environment are not viable management practices.  An integrated program with both management tools is the best approach for achieving effective control because the pathogen is adept at evolving new strains resistant to individual tools: resistant varieties and specific fungicides.  It is more difficult for new pathogen strains to develop when an integrated program is used, and effective control is more likely.  Powdery mildew management program often needs adjustments as the pathogen and management tools frequently change.

The Cucurbit Powdery Mildew photo gallery page has additional information as well as photographs.

cuccurbit powdery mildew on whole plant

Research Topics, Results and Reports

Fungicides and resistant varieties have been evaluated through replicated experiments conducted since 1989 under field conditions at the Cornell University research facility on Long Island.

Fungicide Evaluations – Conventional Products

Fungicide evaluations conducted each year on Halloween-type pumpkin at LIHREC include fungicides at risk for resistance tested alone.  This is neither a recommended nor labeled commercial use pattern for these fungicides; it is done in efficacy evaluations to determine inherent activity of new products and if resistance has affected control of products in commercial use.  Fungicides are applied weekly using a tractor-sprayer to field-grown pumpkin typically starting after reaching the threshold of 1 of 50 older leaves with symptoms in most plots.  Efficacy is assessed by comparing to non-treated plants (control plots) and usually also plants treated with a recommended alternation among labeled fungicides (grower standard without including the recommended protectant fungicide in each application).  A focus has been fungicides at risk for resistance because their targeted activity on fungi, the result of having single site mode of action, means they can move through leaves without causing phytotoxicity and provide control on the underside of leaves where the powdery mildew pathogen develops best.  This research has documented year-to-year variation in efficacy of some fungicides reflecting occurrence of resistance in the pathogen population.  Differences in inherent efficacy among fungicides has also been documented.  These results combined with results from research on fungicide resistance (see below) guide fungicide recommendations for growers.

Table with some results.

Publications:

  1. McGrath, M. T.   Effect of timing of Bayleton application(s) on control of pumpkin powdery mildew, 1989.  Fungicide and Nematicide Tests 45:130.
  2. McGrath, M. T.   Evaluation of fungicides and effect of timing of Bayleton applications on control of pumpkin powdery mildew, 1990.  Fungicide and Nematicide Tests 46:164.
  3. McGrath, M. T.   Efficacy of fungicides applied preventatively or based on disease occurrence for managing powdery mildew of pumpkins, 1991.  Fungicide and Nematicide Tests 47:124.
  4. McGrath, M. T.   Fungicides and integrated use of genetic and chemical control for managing powdery mildew of summer squash, 1991.  Fungicide and Nematicide Tests 47:133.
  5. McGrath, M. T., Ghemawat, M. S., and Staniszewska, H.   Efficacy of fungicides applied preventively or following disease detection for managing powdery mildew of pumpkin, 1992.  Fungicide and Nematicide Tests 48:173.
  6. McGrath, M. T., Ghemawat, M. S., and Staniszewska, H.   Fungicides and integrated use of genetic and chemical control for managing powdery mildew of summer squash, 1992.  Fungicide and Nematicide Tests 48:183.
  7. McGrath, M. T., and Staniszewska, H.   Efficacy of fungicides applied preventively or following disease detection for managing powdery mildew of pumpkin, 1993.  Fungicide and Nematicide Tests 49:142.
  8. McGrath, M. T., and Staniszewska, H.   Fungicides and integrated use of genetic and chemical control for managing powdery mildew of crookneck summer squash, 1993.  Fungicide and Nematicide Tests 49:149.
  9. McGrath, M. T., and Staniszewska, H.   Fungicides and integrated use of genetic and chemical control for managing powdery mildew of straightneck summer squash, 1993.  Fungicide and Nematicide Tests 49:148.
  10. McGrath, M. T.   Evaluation of a biocontrol agent and biocompatible fungicides for managing powdery mildew of winter squash, 1994.  Biological and Cultural Tests 10:149.
  11. McGrath, M. T.   Evaluation of full-season and reduced-sprays fungicide programs initiated after disease detection for managing powdery mildew of pumpkin, 1994.  Fungicide and Nematicide Tests 50:146-147.
  12. McGrath, M. T.   Fungicides and integrated use of genetic and chemical control for managing powdery mildew of summer squash, 1994.  Fungicide and Nematicide Tests 50:157-158.
  13. McGrath, M. T.   Evaluation of fungicide programs initiated after disease detection for managing powdery mildew of pumpkin, 1995.  Fungicide and Nematicide Tests 51:143-144.
  14. McGrath, M. T.   Fungicides and integrated use of genetic and chemical control for managing powdery mildew of squash, 1995.  Fungicide and Nematicide Tests 51:149-150.
  15. McGrath, M. T., and Shishkoff, N.   Evaluation of a biocontrol agent and biocompatible fungicides for managing powdery mildew of melon, 1995.  Biological and Cultural Tests 11:106.
  16. McGrath, M. T.   Evaluation of a biocontrol agent and biocompatible fungicides for managing powdery mildew of pumpkin, 1996.  Biological and Cultural Tests 12:160.
  17. McGrath, M. T.   Evaluation of fungicide programs initiated after disease detection for managing powdery mildew of pumpkin, 1996.  Fungicide and Nematicide Tests 52:138.
  18. McGrath, M. T., and Shishkoff, N.   Evaluation of a biocontrol agent and biocompatible fungicides for managing powdery mildew of melon, 1996.  Biological and Cultural Tests 12:144.
  19. McGrath, M. T., and Shishkoff, N.   Evaluation of fungicide programs initiated after disease detection for managing powdery mildew of pumpkin, 1997. Fungicide and Nematicide Tests 53:227-228.
  20. McGrath, M. T., and Shishkoff, N.   Evaluation of fungicide programs for managing powdery mildew of pumpkin, 1998.  Fungicide and Nematicide Tests 54:230-231.
  21. McGrath, M. T.   Evaluation of fungicide programs for managing powdery mildew of pumpkin, 1999.  Fungicide and Nematicide Tests 55:253-254.
  22. McGrath, M. T., and Shishkoff, N.   Evaluation of fungicide programs for managing powdery mildew of muskmelon, 1999.  Fungicide and Nematicide Tests 55:176-177.
  23. McGrath, M. T.   Alternative fungicides to Bravo evaluated on muskmelon cultivars differing in susceptibility to powdery mildew, 2000.  Fungicide and Nematicide Tests 2001:V75.
  24. McGrath, M. T.   Alternative fungicides to Bravo evaluated on pumpkin cultivars differing in susceptibility to powdery mildew, 2000.  Fungicide and Nematicide Tests 2001:V77.
  25. McGrath, M. T., and Shishkoff, N.   Evaluation of fungicide programs for managing powdery mildew of pumpkin, 2000.  Fungicide and Nematicide Tests 2001:V76.
  26. McGrath, M. T.   Evaluation of fungicide programs for managing powdery mildew of pumpkin, 2001.  Fungicide and Nematicide Tests 57:V86.
  27. McGrath, M. T., and Landers, A.   Efficacy of Bravo for powdery mildew control in muskmelon as affected by nozzle type and sprayer, 2001.  Fungicide and Nematicide Tests 57:V49.
  28. McGrath, M. T., and Landers, A.   Efficacy of Bravo for powdery mildew control in pumpkin as affected by nozzle type and sprayer, 2001.  Fungicide and Nematicide Tests 57:V85.
  29. McGrath, M. T.   Alternative fungicides to Bravo evaluated on muskmelon cultivars differing in susceptibility to powdery mildew, 2001.  Fungicide and Nematicide Tests 57:V48.
  30. McGrath, M. T.   Alternative fungicides to Bravo evaluated on pumpkin cultivars differing in susceptibility to powdery mildew, 2001.  Fungicide and Nematicide Tests 57:V84.
  31. McGrath, M. T.   Efficacy of genetic control and chemical control for managing powdery mildew in winter squash, 2001.  Biological and Cultural Tests 17:V22.
  32. McGrath, M. T., and Shishkoff, N. Evaluation of fungicide programs for managing powdery mildew of pumpkin, 2002. Fungicide and Nematicide Tests 58:V023.
  33. McGrath, M. T. Protectant fungicides for managing powdery mildew of pumpkin, 2002. Fungicide and Nematicide Tests 58:V022.
  34. McGrath, M. T. Efficacy of genetic control and chemical control for managing powdery mildew in butternut-type winter squash, 2002. Biological and Cultural Tests 18:V016.
  35. McGrath, M. T. Efficacy of genetic control, used alone and combined with fungicides, for managing powdery mildew in acorn-type winter squash, 2002. Biological and Cultural Tests 18:V015.
  36. McGrath, M. T. Efficacy of Bravo for powdery mildew control in muskmelon and pumpkin as affected by nozzle type and sprayer, 2003. Fungicide and Nematicide Tests 59:V057.
  37. McGrath, M. T. Efficacy of genetic control, used alone and combined with fungicides, for managing powdery mildew in acorn-type winter squash, 2003 Biological and Cultural Tests 19:V018.
  38. McGrath, M. T. Efficacy of genetic control and chemical control for managing powdery mildew in butternut-type winter squash, 2003. Biological and Cultural Tests 19:V019.
  39. McGrath, M. T. Evaluation of biofungicides and compost tea for managing powdery mildew of pumpkin, 2003. Fungicide and Nematicide Tests 59:V055.
  40. McGrath, M. T. Evaluation of fungicide programs for managing powdery mildew of pumpkin, 2003. Fungicide and Nematicide Tests 59:V056.
  41. McGrath, M. T. Comparison of powdery mildew resistant pumpkin and winter squash under reduced-fungicide program, 2004. Biological and Cultural Tests 20:V011.
  42. McGrath, M. T. Evaluation of biofungicides and compost tea for managing powdery mildew of pumpkin, 2004, Fungicide and Nematicide Tests 60:V050.
  43. McGrath, M. T. Evaluation of biofungicides for managing powdery mildew of pumpkin, 2004. Fungicide and Nematicide Tests 60:V051.
  44. McGrath, M. T. Evaluation of fungicide programs for managing pathogen resistance and powdery mildew of pumpkin, 2004. Fungicide and Nematicide Tests 60:V049.
  45. McGrath, M. T. Experimental fungicides compared to fungicides registered for managing powdery mildew of winter squash, 2004. Fungicide and Nematicide Tests 60:V056.
  46. McGrath, M. T., and Davey, J. F. 2006. Evaluation of biofungicides for managing powdery mildew of pumpkin, 2005. Fungicide and Nematicide Tests 61:V036.
  47. McGrath, M. T., and Davey, J. F. 2006. Evaluation of copper fungicides for managing powdery mildew of pumpkin, 2005. Fungicide and Nematicide Tests 61:V037.
  48. McGrath, M. T., and Davey, J. F. 2006. Evaluation of fungicide programs for managing powdery mildew of pumpkin, 2005. Fungicide and Nematicide Tests 61:V038.
  49. McGrath, M. T., and Davey, J. F. 2006. Experimental fungicide compared to fungicide registered for managing powdery mildew of winter squash, 2005. Fungicide and Nematicide Tests 61:V039.
  50. McGrath, M. T., and Davey, J. F. 2007. Evaluation of biofungicides for managing powdery mildew of pumpkin, 2006. Plant Disease Management Reports 1:V145.
  51. McGrath, M. T., and Davey, J. F. 2007. Evaluation of fungicides for management of powdery mildew on pumpkin, 2006. Plant Disease Management Reports 1:V144.
  52. McGrath, M. T., and Davey, J. F. 2007. Evaluation of fungicides for the management of powdery and downy mildews of winter squash, 2006. Plant Disease Management Reports 1:V140.
  53. McGrath, M. T., and Fox, G. M. 2008. Evaluation of fungicides for managing powdery mildew in pumpkin, 2007. Plant Disease Management Reports 2:V142.
  54. McGrath, M. T., and Fox, G. M. 2008. Evaluation of an integrated management program with fungicides and a resistant cultivar for managing powdery mildew in zucchini squash, 2007. Plant Disease Management Reports 2:V148.
  55. McGrath, M. T., and Fox, G. M. 2008. 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.
  56. McGrath, M. T., and Fox, G. M. 2008. Evaluation of integrated management programs with biofungicides and a resistant cultivar for managing powdery mildew in muskmelon, 2007. Plant Disease Management Reports 2:V078.
  57. McGrath, M. T., and Fox, G. M. 2008. Evaluation of integrated management programs with biofungicides and a resistant cultivar for managing powdery mildew in pumpkin, 2007. Plant Disease Management Reports 2:V141.
  58. McGrath, M. T., and Fox, G. M. 2009. Efficacy of fungicides for managing cucurbit powdery mildew and treatment impact on pathogen sensitivity to fungicides, 2008. Plant Disease Management Reports 3:V125.
  59. 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.
  60. McGrath, M. T., and Fox, G. M. 2010. Efficacy of fungicides for managing cucurbit powdery mildew and treatment impact on pathogen sensitivity to fungicides, 2009. Plant Disease Management Reports 4:V147.
  61. McGrath, M. T., and Fox, G. M. 2010. Integrated programs with biopesticides and a resistant cultivar evaluated for powdery mildew in butternut squash, 2009. Plant Disease Management Reports 4:V024.
  62. McGrath, M. T., and Fox, G. M. 2010. Integrated programs with biopesticides and a resistant cultivar evaluated for powdery mildew in muskmelon, 2009. Plant Disease Management Reports 4:V025.
  63. McGrath, M. T., and Fox, G. M. 2010. Integrated programs with biopesticides and a resistant cultivar evaluated for powdery mildew in pumpkin, 2009. Plant Disease Management Reports 4:V114.
  64. McGrath, M. T., and Hunsberger, L. K. Efficacy of fungicides for managing cucurbit powdery mildew and pathogen sensitivity to fungicides, 2010.  Plant Disease Management Reports 5:V104.
  65. McGrath, M. T., and Hunsberger, L. K.   Efficacy of fungicides for managing powdery mildew in muskmelon, 2010.  Plant Disease Management Reports 5:V103.
  66. McGrath, M. T., and Hunsberger, L. K. Efficacy of fungicides for managing cucurbit powdery mildew and pathogen sensitivity to fungicides, 2011. Plant Disease Management Reports 6:V080.
  67. McGrath, M. T., and Hunsberger, L. K. Efficacy of Vivando for managing powdery mildew in cucurbit crops, 2011. Plant Disease Management Reports 6:V007.
  68. McGrath, M. T. and LaMarsh, K. A.   Efficacy of fungicides for managing powdery mildew in pumpkin, 2012.  Plant Disease Management Reports 7:V013.
  69. McGrath, M. T. and LaMarsh, K. A.   Comparison of organic and conventional copper fungicides for powdery mildew in zucchini, 2013. Plant Disease Management Reports 8:V193.
  70. McGrath, M. T. and LaMarsh, K. A.   Efficacy of fungicides for managing powdery mildew in pumpkin, 2013.  Plant Disease Management Reports 8:V204.
  71. McGrath, M. T. and LaMarsh, K. A.   Efficacy of fungicides for managing powdery mildew in pumpkin, 2014.  Plant Disease Management Reports 9:V030.
  72. McGrath, M. T.   Efficacy of fungicides for managing powdery mildew in pumpkin, 2015.  Plant Disease Management Reports 10:V040.
  73. McGrath, M. T. and Sexton, Z. F.   Efficacy of biopesticides for managing powdery mildew in pumpkin, 2016.  Plant Disease Management Reports 11:V025.
  74. McGrath, M. T. and Sexton, Z. F.   Efficacy of fungicides for managing powdery mildew in pumpkin, 2016.  Plant Disease Management Reports 11:V024.
  75. McGrath, M. T. and Sexton, Z. F.   Evaluation of management programs without chlorothalonil for powdery mildew in pumpkin, 2016.  Plant Disease Management Reports 11:V026.
  76. McGrath, M. T. and Sexton, Z. F.   Efficacy of fungicides for managing powdery mildew in pumpkin, 2017.  Plant Disease Management Reports 12:V067.
  77. McGrath, M. T. and Sexton, Z. F.   Evaluation of fungicides to reduce chlorothalonil use for powdery mildew on pumpkins, 2017.  Plant Disease Management Reports 12:V073.
  78. McGrath, M. T. and Sexton, Z. F.   Efficacy of fungicides for managing powdery mildew on pumpkin, 2018.  Plant Disease Management Reports 13:V119.
  79. McGrath, M. T. and Sexton, Z. F.   Evaluation of fungicides to reduce chlorothalonil use for powdery mildew on squash, 2018.  Plant Disease Management Reports 13:V122.
  80. McGrath, M. T. and Sexton, Z. F.   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.
  81. McGrath, M. T. and Sexton, Z. F.   Efficacy of organic fungicides for managing powdery mildew on acorn squash, 2018.  Plant Disease Management Reports 13:V121.

Fungicide Resistance – Summary Results

Procedures and Reports are below

Resistance to FRAC code 1 fungicides (ex. Topsin M) and FRAC code 11 fungicides (ex. Flint, Quadris) has been found at a high frequency for many years.  Both are qualitative type of resistance which means pathogen isolates are either sensitive or resistant to all fungicides in these chemistry groups.  None are recommended.

Resistance to FRAC code 7 fungicides has also been found to be common.  Resistance is partial among fungicides in this chemistry group which means pathogen isolates are fully resistant to some fungicides (ex. Endura, Pristine, Merivon) but sufficiently sensitive to others (ex. Luna fungicides) that they are able to suppress resistant isolates.  This reflects differences in how these fungicides bind to the active site in the fungus.

Resistance to FRAC code 3 fungicides was first detected in 1989 and was associated with control failure of Bayleton, the fungicide in use then.  This fungicide has been replaced by several fungicides in this chemistry group that vary in inherent activity but are all more effective than Bayleton reflecting the quantitative type of resistance to this chemistry.  The pathogen has not exhibited further development of resistance (increased insensitivity) to FRAC code 3 fungicides thus they remain an important component of fungicide program for cucurbit powdery mildew. Recommended fungicides include Proline, Procure, Rhyme, and Luna Experience which also has a FRAC code 7 ingredient.

Resistance to FRAC code 13 fungicide (Quintec) was first detected in 2015.  While detected in pathogen isolates collected at the end of powdery mildew development (September), resistance has not been detected early (July) and Quintec has continued to provide good control of powdery mildew until 2019.  This fungicide is recommended used sparingly and early in powdery mildew development.

Resistance to FRAC code U6 fungicide (Torino) was detected in 2017.  Detection was associated with control failure in the fungicide efficacy trial at LIHREC. Resistance has been detected since, including early in powdery mildew development in 2019 (July).  This fungicide is no longer recommended.

Pathogen isolates with resistance to multiple fungicide chemistry groups have been found.  Their presence complicates managing resistance and powdery mildew. Resistant isolates have been detected in plantings not treated with any targeted fungicides indicating they can compete with sensitive isolates (no fitness cost to resistance).

Resistance has not been detected to FRAC code 50 fungicides (ex Vivando).

Fungicide Resistance – In-Field Seedling Bioassays

The bioassay entails treating potted seedlings at about the 3-leaf stage with different fungicide doses, putting them in field locations next to plants naturally affected by powdery mildew for a day, then keeping them in a greenhouse until symptoms develop when upper surface of each leaf is assessed for severity based on percent coverage with visible symptoms. Efficacy of each treatment is assessed by comparing severity to that on non-treated control plants.

Detailed description of procedure.

infected seedlings in pots

Fungicide Resistance – Laboratory Leaf Disk Bioassays

Pathogen isolates (individuals) are obtained from single powdery mildew colonies (lesions) on field-grown leaves. They are maintained on cotyledons in petri dishes until tested in a bioassay. For the bioassay, seedlings at the cotyledon stage are treated with different fungicide doses, the next day leaf disks are cut from the cotyledons and placed on water agar in a Petri dish, then the disks are inoculated by transferring spores from a culture to the center of each disk. About 10 and 14 days later severity is assessed on each disk. Typically isolates either do not grow or grow well often not showing obvious reduction in growth compared to non-treated disks

Detailed description of procedure.

leaf disk assay for powdery mildew

Publications about fungicide resistance:

  1. McGrath, M. T., and Hausbeck, M. K.   Insensitivity of Sphaerotheca fuliginea to triadimefon in a commercial pumpkin field in Michigan.  Plant Disease 77:319.
  2. McGrath, M. T.   Increased resistance to triadimefon and to benomyl in Sphaerotheca fuliginea populations following fungicide usage over one season.  Plant Disease 80:633-639.
  3. McGrath, M. T, Staniszewska, H., Shishkoff, N., and Casella, G.   Fungicide sensitivity of Sphaerotheca fuliginea populations in the United States.  Plant Disease 80:697-703.
  4. McGrath, M. T., and Shishkoff, N.   Resistance to triadimefon and benomyl: dynamics and impact on control of cucurbit powdery mildew.  Plant Disease 85(2):147-154.
  5. McGrath, M. T.   Fungicide resistance in cucurbit powdery mildew: Experiences and challenges.  Plant Disease 85(3):236-245. (Feature article).
  6. McGrath, M. T., and Shishkoff, N. First report of the cucurbit powdery mildew fungus (Podosphaera xanthii) resistant to strobilurin fungicides in the United States. Plant Disease 87:1007.
  7. Lebeda, A., McGrath, M. T., and Sedlákova, B.   Fungicide resistance in cucurbit powdery mildew fungi. Chapter 11. Pages 221-246 In Fungicides. Carisse, O. (Ed.).  InTech Publishers, Vienna, Austria.  (ISBN 978-953-307-266-1).
  8. McGrath, M. T.   Challenge of fungicide resistance in managing vegetable diseases in United States and anti-resistance strategies.  Chapter 16.  Pages 191-207.  In Fungicide Resistance in Crop Protection: Threat and Management.  Thind, T. S. (Ed.).  CABI International, Wallingford, UK.
  9. McGrath, M. T.   Cucurbit powdery mildew in the USA.  Chapter 25.  Pages 401-417.  In Fungicide Resistance in Plant Pathogens: Principles and a Guide to Practical Management.  H. Ishii and D. W. Hollomon (Eds.).  Springer Japan KK, Tokyo.
  10. McGrath, M. T. and Wyenandt, C. A.   First detection of boscalid resistance in Podosphaera xanthii in the United States associated with failure to control cucurbit powdery mildew in New York and New Jersey in 2009.  Plant Health Progress 18:93.
  11. McGrath, M. T.   First report of resistance to quinoxyfen in Podosphaera xanthii, causal agent of cucurbit powdery mildew, in the United States.  Plant Health Progress 18:94.
  12. Wyenandt, C. A., McGrath, M. T., Everts, K. L., Rideout, S. L., Gugino, B. K., and Kleczewski, N.   Fungicide resistance management guidelines for cucurbit downy and powdery mildew control in the mid-Atlantic and Northeast regions of the United States in 2018.  Plant Health Progress 18:1-3.
  13. McGrath, M. T. and Sexton, Z. F.   Fungicide sensitivity of cucurbit powdery mildew pathogen population on Long Island, NY, determined with seedling bioassay, 2017.  Plant Disease Management Reports 12:V153.
  14. McGrath, M. T. and Sexton, Z. F.   Poor control of cucurbit powdery mildew associated with first detection of resistance to cyflufenamid in the causal agent, Podosphaera xanthii, in the United States. Plant Health Progress 19:222-223.
  15. Leadbeater, A., McGrath, M. T., Wyenandt, C.A., and Stevenson, K. L.   An Overview of Fungicide Resistance and Resistance Management – History and Future Trends.  Chapter 1.  Pages 3-19.  In Fungicide Resistance in North America, Second Edition.  APS Press, St Paul.
  16. McGrath, M. T., Sexton, Z. F., and Nadel, S.   Fungicide sensitivity of cucurbit powdery mildew pathogen populations on Long Island, NY, determined using a seedling bioassay, 2018.  Plant Disease Management Reports 13:V161.
  17. McGrath, M. T., Wyenandt, C.A., and Stevenson, K. L.   Occurrence of Fungicide Resistance in Pathogens of Non-Solanaceous Vegetable Crops.  Chapter 23.  Pages 309-332.  In Fungicide Resistance in North America, Second Edition.  APS Press, St Paul.

Fungicide Evaluations – Biopesticides and other Organic Products – on another webpage

Plant Resistance Evaluations – New and Experimental Varieties – coming soon

 

 

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