Cause A bacterium, Pseudomonas syringae pv. maculicola, causes this disease, also known as bacterial leaf spot on cauliflower, broccoli, and Brussels sprouts. Bacteria survive on infested seed and crop residues as well as in soil. Cool, wet weather, common west of the Cascade Range, favors disease development before harvest in the fall.
Symptoms Tiny black to purplish spots appear on outer leaves. Yellow halos appear around the spots, and they eventually grow together to form light brown, papery areas. Symptoms may vary depending on the pathogen strain present in the field.
Cultural control
- Plant pathogen-free seed.
- Avoid sprinkler irrigation in the seedbed once the crop has germinated and established. In the greenhouse, ebb and flow irrigation is preferred to overhead sprinkling.
- Shred and turn under diseased crop refuse promptly after harvest to hasten breakdown of infected plant material.
- Do not plant Brassica crops the following year if the field has a significant level of infection.
Chemical control
- Cueva at 0.5 to 2 gal/100 gal water on 7- to 10-day intervals. May be applied on the day of harvest. 4-hr reentry. O
Biological control Efficacy unknown in Oregon.
- Cease at 3 to 6 quarts in 100 gal water. For greenhouse plants only. Preharvest interval is 0 days. 4-hr reentry. O
Reference Wiebe, W.L., and Campbell, R.N. 1993. Characterization of Pseudomonas syringae pv. maculicola and comparison with P. s. tomato. Plant Disease 77:414-419.