White leaf spot is a fungal disease common to Brassicas. remove any diseased plants immediately to prevent disease spread and build-up in the planting location. When present, avoid overhead sprinkler irrigation if possible as this causes water-splash spread which makes the disease worse. Only work in garden beds when leaves are dry to prevent spread of disease through contact with hands, tools or clothing.
Pests
Flea beetles will feed on the leaves which may cause the harvest to be unmarketable. Use row covering protect plants from egg-laying adults.