Urbana, Illinois, USA
July 31, 2015

Downy mildew of cucurbits is a destructive disease of cucurbits, including pumpkins. According to a University of Illinois vegetable and fruit pathologist, infection in a pumpkin field has shown up in Illinois.  

Mohammad Babadoost explained that downy mildew of cucurbits was recently diagnosed by colleague Daniel Egel in a watermelon field in Lawrence County, Ill., on July 23. “I was hoping that the disease would not spread to other parts of the state. But yesterday (July 30), we observed severe infection by downy mildew pathogen in a processing pumpkin field in Mason County, Ill.,” Babadoost said. “The pathogen will likely spread to other parts of the state.”

Downy mildew of cucurbits, caused by Pseudoperonospora cubensis, is a very destructive disease of cucurbits. “The present strain of the pathogen will likely infect all cucurbit crops, including cucumber, gourd, muskmelon, pumpkin, squash, and watermelon,” Babadoost said.  “Weather conditions in Illinois are very conducive for development of downy mildew.”

Downy mildew affects leaves only. Symptoms of downy mildew vary with the host and the environmental conditions. Babadoost explained that the first symptom is usually the appearance of indistinct pale green areas on the upper leaf surface. The pale green areas soon become yellow in color and angular to irregular in shape, bounded by the leaf veins.

“As the disease progresses, the lesions may remain yellow or become brown and necrotic. During moist weather, the corresponding lower leaf surface is covered with a downy, pale gray to purple mildew. Often an upward leaf curling will occur,” he added.

If you don’t have the disease in your field yet, Babadoost recommends including chlorothalonil (e.g., Bravo Weather Stik) in weekly sprays. If downy mildew is observed in the field, spray cucurbit crops with one the following fungicide combinations at weekly intervals: Revus 2.09SC or Previcur Flex 6SC or Tanus 50WG or Ranman 3.6SC or Gavel 75DF or Zampro 525F plus chlorothalonil. 

For additional information, contact Babadoost at babadoos@illinois.edu or 217-333-1523. 

Website: http://www.uiuc.edu

Published: July 31, 2015