Infection and susceptibility
Ideal conditions for clubroot infection are:
- acidic soils
- high soil moisture
- warm temperatures (20-25°C)
- presence of susceptible brassica host.
Infection can occur in soils where the ideal conditions are not met however the disease will be less severe.
Infection in the plant’s root hairs takes place soon after brassica plants contact infested soil. Further infective spores are rapidly produced in the plant roots and the characteristic swelling of the roots occurs. The spores can infect adjacent roots and nearby brassica plants. Plants are susceptible to the clubroot pathogen at all growth stages.
Brassica crops vary in their susceptibility to clubroot. Chinese cabbage is very sensitive to the disease. Cauliﬂower is less susceptible but more susceptible than broccoli and head cabbage. There is also different tolerance to clubroot between varieties within each species.
As there are several strains, crop tolerance to one strain of clubroot may not mean the crop is tolerant to other strains of this disease.
Farm hygiene is very important in preventing the spread of the clubroot pathogen to new properties and reducing the risk of the disease spreading to non-infested areas on infested properties. The disease can be transported in soil on machinery, farm implements, footwear, livestock or vehicles. Clubroot spores can also be spread in water.
Good on-farm hygiene practices include:
- Thoroughly clean all equipment that enters and leaves a farm, using high pressure washing, to ensure that soil is not being transported.
- Work from the least infested areas of the farm to those that are the most infested.
- Purchase high quality seedlings from a reputable source and avoid placing racks and trays on the ground.
- Where possible, irrigation dams should not receive run-off from infested paddocks. Where this is not possible, irrigation water should be taken from the surface, in the stillest part of the dam. Clubroot spores will settle to the bottom, so avoid taking the muddy water from near the bottom of a dam.
- Erect signs asking visitors to respect your farm hygiene. Visitors and workers should report to a designated area, such as the office, prior to entering the farm and be aware of your farm hygiene protocols.