Downy mildew was found on cucumbers in Wayne County, Ohio, from two separate locations last week. One sample came from an unsprayed private garden near Wooster and another from a 2-A commercial field in West Salem. Disease incidence in the commercial field was about 1%; it had been sprayed on June 8 with Previcur Flex + protectant. The severity on infected leaves was moderate but sporulation in the lesions was high.

This is significantly (about 2-3 weeks) earlier than we have seen in the past few years. It is also surprising since the weather has been very dry and sunny in the locations downy mildew was found. However, recent cool nights and heavy dews were apparently sufficient for an outbreak.

Although so far we have only found downy mildew in Wayne County, previous experience leads us to expect it is likely to be present in other northern counties. Therefore cucumber growers in northern Ohio should begin downy mildew preventative fungicide programs if they have not already done so.

Melons, particularly cantaloupes, are next to cucumbers in susceptibility to downy mildew. Preventative fungicide programs should also be initiated at this time. Please send us samples to your local OSU Extension Office if you suspect downy mildew in cucumbers, melons or other vine crops.

A detailed factsheet can be found here:
http://go.osu.edu/DownyMildew2
From Dr. Sally Miller – Vegetable Disease Specialist, Ohio State University Extension
SUGGESTED DOWNY MILDEW MANAGEMENT PROGRAMS FOR CUCUMBERS AND MELONS:
Fungicide application:
Protection before disease appears: Apply one of the following fungicides on a 7-10 day schedule, tank mixed with Bravo, Manzate or Dithane: Presidio, Ranman, Previcur Flex, Tanos, Curzate or Gavel (Gavel already contains mancozeb). Alternate products. The application interval can be lengthened under dry conditions. Use the shorter interval under cool, moist conditions.
Management after disease appears: Apply one of the following fungicides on a 5-7 day schedule, tank mixed with Bravo or Dithane: Presidio, Ranman, Previcur Flex, or Tanos. Alternate products. The application interval can be lengthened under dry conditions. Use the shorter interval under cool, moist conditions. See product labels for fungicide rates.
Most recent research has shown that fungicides can be ranked as follows for efficacy against downy mildew: Presidio = Ranman > Previcur Flex > Curzate > Gavel > Mancozeb = Bravo.
Note that the fungicides recommended above have different preharvest intervals (PHI). Keep this in mind when fungicides are applied after harvesting begins.
Product PHI (days)
Bravo Weather Stik 0
Ranman 0
Previcur Flex 2
Tanos 3
Dithane or Manzate 5
Gavel 5
Presidio 2
Curzate 3

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