1. Powdery mildew fungus (Podosphaera xanthii)
Likelihood: HighPrimary pathogen on cucumber leaves and stems that produces powdery white spores visible on the upper leaf surface. Spores germinate and spread under warm daytime temperatures and moderate humidity; they do not require free water on the leaf surface to infect but will take advantage of prolonged leaf wetness and dense canopies.
Identification
- remove_circle_outlineWhite or grayish powdery patches primarily on the upper leaf surface that can be rubbed off.
- remove_circle_outlineEarly circular spots that expand and coalesce into large patches causing leaf yellowing and curling.
- remove_circle_outlineIn severe cases, stems and occasional fruit surfaces show powdery growth and surface blemishes.
- remove_circle_outlineSymptoms often begin on older, lower leaves in the interior of the canopy.
