Downy mildew on pumpkins in Ohio

Downy mildew was found this week in organic pumpkins in Harrison County. Options for downy mildew control are limited in organic cucurbits, and at this point in the growing season the damage may not significantly affect yield. Downy mildew affects pumpkin leaves but not vines or fruit.  The main danger, once fruits have matured, is defoliation and subsequent sunburn of the fruit. If plants are defoliated, and sunny weather is expected, fruits should be removed from the field and stored in the shade.

Previously this summer we found downy mildew on cucumbers and cantaloupes in our sentinel plots and on commercial farms.  The disease appeared on cucumbers/melons much later in the growing season than expected, first detected on August 22.  The strain of the downy mildew pathogen that appears early, usually in early July, is thought to originate in greenhouses in the Great Lakes region.  This strain only affects cucumbers and melons, and we don’t know why the early introductions did not happen this year. The strain that infects all cucurbits originates in the South, always arrives in August or later, and is likely the main culprit this year. We are currently testing isolates to identify the strain type from plants we’ve collected in Ohio.



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