Early symptoms of downy mildew on a cucumber leaf. Image by Francesca Rotondo.
Downy mildew was found on cucumbers in central Wayne County, OH today. This is a bit early for downy mildew in this state, indicating that unless we experience an extended dry spell, downy mildew disease pressure may be significant this growing season. Don’t be fooled by the hot weather – the downy mildew pathogen prefers moderate temperatures, but as long as there is rainfall to drop the spores onto one’s crop and high humidity, the pathogen does just fine. It hides in the crop canopy on the underside of leaves, which protect them from the sun. Moderate nighttime temperatures provide the opportunity for the pathogen to infect the leaves.
Underside of cucumber leaf showing sporulation of the downy mildew pathogen. Image by Francesca Rotondo.
Management recommendations are cited in yesterday’s post.
Oval sporangia (spores) of the downy mildew pathogen, Pseudoperonspora cubensis. Micrograph by Francesca Rotondo.