Clubroot is a common disease of the Brassica family, caused by the soil-born pathogen Plasmodiophora brassicae that can infect cabbage, broccoli, cauliflower, Chinese cabbage, and others. It can survive for years in the soil as resting spores before the presence of a susceptible host stimulates germination of these spores.
Infection begins in the root hairs and later the main roots become swollen and will often develop galls. Infected roots become dysfunctional, leading to yellowing, wilting and stunting of plants and ultimately general decline and death. The infected roots, often resembling thick fingers, make identification of the disease relatively easy.
Spores are spread by the movement of infected soil on implements, footwear and livestock. They are also waterborne so can spread in run-off water from infected areas. When soil conditions are favourable and a susceptible host is present, the resting spores germinate and produce zoospores which are mobile in soil water. These “swim” to root hairs and the disease cycle begins. Germination can occur between 120C and 270C with soil temperatures between 180C and 250C ideal.
There are no means of eradicating the disease from infested soil and no chemical treatment. There are however management practices that can minimize its’ impact.
Crop rotation is very important, planting the same family of crop in the same field should be avoided for a period of at least 4 years. For rotation to be effective, it is important to eliminate any alternate hosts during the intervening years.
Limit movement of machinery, people and livestock between infected and clean areas. If infected areas are to be worked, clean any machinery thoroughly before moving to another area. Where possible, infected areas should be worked last in a day and the cleaned equipment allowed to dry overnight. No soil or infected plant material should leave the suspect area. Hygiene measures such as footbaths or dedicated footwear for use in infected areas can be implemented. All staff and visitors must be made aware of the threat and all sanitation protocols.
Waterways should be regularly maintained to prevent any water from infected areas getting into clean areas.
