Plant Disease Management Handbook

Cause The fungi or fungus-like microorganisms, Pythium spp., Fusarium spp., and Rhizoctonia solani, attack young seedlings of many vegetables, including members of the genus Brassica. These soilborne microorganisms can persist indefinitely in soil or plant debris. If seedlings are affected before emergence, it appears as poor germination.

A Chinese cabbage plant exhibiting swollen roots at the base of the plant due to clubroot. Photo by Cynthia M. Ocamb, 2020.
Image related to Cabbage and Cauliflower (Brassica sp.)-Light Leaf Spot
Image related to Cabbage and Cauliflower (Brassica sp.)-Black Leg (Phoma Stem Canker)

Cause The soft-rot bacterium, Erwinia carotovora subsp. carotovora (syn. = Pectobacterium carotovorum subsp. carotovorum), enters through growth cracks or wounds caused by cold temperatures, insects, other disease organisms, or by mechanical means.

Image related to Cabbage and Cauliflower (Brassica sp.)-Black Spot (Leaf, Stem, or Pod Spots)

By K. F. Ward, L. du Toit, and C. M. Ocamb