Cucumber downy mildew (CDM) was confirmed on a cucumber sample from a production field in Wilson County on June 8 of 2020. Leaves presented approximately 20% disease (Figure 1 and 2), and 30% of the field was affected.
Angular, chlorotic lesions on the upper surface of cucurbit leaves and gray sporulation on the underside are characteristic symptoms and signs of CDM (Figure 1). For confirmation, sporangiophore structures typical of the causal agent (Pseudoperonospora cubensis), were observed on the underside of the leaf using a hand lens (Figure 2).
Figure 1. Angular, yellow lesions on topside of the leaves that are bound by leaf veins (Mike Adams, NC State Vegetable Pathology Lab)
Figure 2. Dark spores on underside of the leaf (Mike Adams, NC State Vegetable Pathology Lab).
