Symptoms
Shiny white, blister-like pustules on the undersides of leaves, with pale yellow patches on the upper surface above them. Heavy infection distorts and swells stems and flower heads (stagheads).
Prevention
Space plants for airflow, avoid overhead watering and remove infected leaves early. Rotate crops and clear cruciferous weeds that host the pathogen.
Treatment
Organic
Spray a copper-based fungicide at first pustules and remove blistered leaves. Improve airflow and keep foliage dry to slow spread.
Chemical (last resort)
Apply metalaxyl or a mancozeb-based fungicide at early symptoms during humid weather. Rotate oomycete-active groups and observe PHI on leafy crops.
Affects 1 crop
Sources
MARDI Brassica Production Guide; DOA IPM Manual