Downy mildew was confirmed on a pumpkin sample from Pike County, OH today. This is the second southern Ohio county with a recent downy mildew outbreak. Pumpkins and squash in southern and central Ohio need to be protected from downy mildew with fungicides. Downy mildew has been widespread in northern and central Ohio in cucumbers and melons much of the summer, but has not been reported yet in squash or pumpkins. Both crops should be scouted regularly for downy mildew symptoms in northern Ohio counties. There is evidence that many of the fungicides previously used for downy mildew management have become ineffective due to the development of insensitivity in the downy mildew pathogen. It is critical to include a protectant fungicide, e.g. chlorothalanil, in a tank mix with a downy mildew fungicide such as Ranman. Ranman must be alternated with a fungicide with a different mode of action, such as Zing!, which also contains chlorothalanil in a premix with zoxamide. Dr. Mohammad Babadoost of the University of Illinois has noticed that commercial pie pumpkins treated with Bravo Weather Stik (chlorothalanil) develop symptoms, but the pathogen does not sporulate well in the lesions, resulting in much slower spread than in non-sprayed pumpkins. We don’t know if the southern and central Ohio downy mildew pathogen “type” is the same as the Illinois type, and will respond in the same way, but if so growers may benefit from the use of chlorothalanil in a protectant program for pumpkin downy mildew.
Keep in mind that pumpkins also need to be protected from powdery mildew. Quintec and Torino are two of several effective fungicides to manage this disease.