Downy Mildew on brassica (cabbage & broccoli) seedlings

Description: Scattered, irregular-shaped, sunken, gray-black lesions on a mixed sample of cabbage and broccoli seedlings. Symptoms ranged from subtle (broccoli) to more severe (cabbage).


Tests done: The diagnostician had already recognized this as downy mildew (based on experience), but I decided to place leaves in a moist chamber to induce sporulation just to double-check.

Final Diagnosis: Downy mildew caused by Peronospora parasitica. Forgot to take a picture of the diagnostic sporangiophores and sporangia! The University of Florida has a good factsheet describing symptoms, although the accompanying photos seem over-exposed.

References used: Compendium of Brassica Diseases