Cucurbit Downy Mildew Update – 12 June, 2012

Cucurbit downy mildew remains active in the Southern United States, with recent reports in the Carolinas and in Maryland.  While the risk for Ontario remains low at this time, direct-seeded cucumber growers should start a preventative fungicide program no later than vine development.  Under wet weather conditions, or periods of prolonged leaf wetness due to heavy dewfall, be prepared to start earlier if necessary.

For growers of transplanted cucumbers and melons, begin a preventative disease management program as soon as the crop is transplanted in the field.

Under low risk conditions, apply a broad spectrum fungicide every 7-10 days.  If downy mildew is confirmed in the Great Lakes basin, or if weather conditions are conducive to its spread, switch to a targeted downy mildew product every 5-7 days.

Broad Spectrum Fungicides Targeted Downy Mildew Fungicides
  • chlorothalonil (Bravo 500)
  • mancozeb (Dithane DG, Penncozeb 80 WP, Manzate Pro-stick)
  • cyazofamid + surfactant (Ranman 400SC)
  • propamocarb/chlorothalonil (Tattoo C)
  • fluopicolide + chlorothalonil (Presidio + Bravo 500)

Always rotate between fungicides from different chemical families. Do not make sequential applications of any one fungicide.

• Use a minimum spray volume of 30-60 gallons per acre.

• Apply a preventative fungicide before a rainfall event

• Apply a preventative fungicide prior to overhead irrigation.

Foliar fungicides in the strobilurin or QoI family (group # 11) pose a high risk of developing resistance and have not performed consistently in research trials. Due to the highly infectious nature of this disease, group 11 fungicides are not recommended for downy mildew control in Ontario.

Visit the IPMpipe website at: http://cdm.ipmpipe.org/ for a map of confirmed downy mildew infections across North America.

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