These are symptoms of clubroot disease, which affects the brassica family. In greenhouse production, methods of soil treatment such as soil solarisation help to kill the fungus. Soil solarisation is done by leaving a clear plastic polythene sheet on the soil surface for four-to-six weeks during the hot season. Soil solarisation should be done before planting. Consider your soil type as this is an important factor in the development and spread of cabbage clubroot.

Source: Daily Nation July 03, 2020 21:00 UTC