Clubroot disease, caused by the pathogen Plasmodiophora brassicae, is a common disease that affects the brassica family, such as Cabbage and Brussels sprouts, causing swollen, distorted roots and stunting plant growth. Clubroot typically strikes from mid-summer to late autumn when the soil is moist and warm and can persist in the soil for up to 20 years.
While many people describe clubroot as a fungal infection, it’s actually a protist, an organism distinct from animals, land plants, or fungi. It is closely related to slime molds that can affect lawns. It produces resting spores, and in the presence of roots from a plant of the brassica family, the spores germinate, infecting the roots. The pathogen produces more resting spores in the roots of the plant, which eventually rot, releasing them back into the soil.
Symptoms
- Above ground: Plants are stunted in growth with purplish foliage and will often wilt in hot weather. Badly infected plants will often die.
- Below ground: The roots of the plant will become swollen and distorted with very few finer roots.
Controlling and Treating ClubRoot
- Clubroot can be easily spread by the plants themselves. When buying plants, ensure they come from a guaranteed clubroot-free source, and be extra cautious when swapping plants with friends.
- Raising the pH level of the soil can reduce the effects of clubroot. This can be done by regularly applying lime to your soil. Apply roughly 270-500g per square meter every year. You can apply lime to the surface of the soil in the winter months. This will give the lime time to take effect before you start planting in the spring.
- Improving soil drainage can also help. Add plenty of organic matter or even build raised beds, for example.
- Regularly clean and disinfect tools, wheelbarrows, and footwear.
- Certain varieties of the brassica family exhibit resistance to clubroot. For instance, Cryptus F1 (Brussels sprouts) and Tall Green Curled (Kale) show some resistance, so it’s worth seeking out these varieties if you are suffering from clubroot.
- Unfortunately, no chemicals are available to treat clubroot.