Clubroot of cabbage

Clubroot is a devastating soil-borne disease affecting cruciferous crops, caused by the obligate parasite Plasmodiophora brassicae. This pathogen infects the roots of cabbage, broccoli, cauliflower, Brussels sprouts, kale, and other related species. It is considered one of the most challenging diseases for growers globally due to the long persistence of its resting spores in the soil environment.

The primary symptom of clubroot is the formation of characteristic galls or swellings on the roots, which disrupt the plant's ability to transport water and nutrients. Above-ground symptoms include stunted growth, wilting during warmer parts of the day, and yellowing of the lower leaves. As the disease progresses, the galls decay, which eventually kills the plant and releases millions of new spores into the soil.

The development of Plasmodiophora brassicae is favored by acidic soil conditions and high moisture levels. Resting spores can remain viable in the soil for many years, even in the absence of a host crop. The disease can be spread through contaminated soil transported by farm machinery, infected nursery transplants, drainage water, or movement of infested soil from one field to another.

The economic impact of clubroot is substantial, as it can cause complete crop failure in heavily infested areas. Once the soil is contaminated, it remains a long-term risk for any brassica crops. Beyond direct yield losses, the infection affects the quality and uniformity of the produce, often rendering the crop unmarketable or unsuitable for mechanical harvesting.

Management of clubroot is focused on long-term prevention since there are no complete curative treatments for infested soil. Effective strategies include:

• Practicing strict crop rotation (at least 6-8 years between host crops).
• Increasing soil pH to 7.2 or higher using lime applications.
• Using clubroot-resistant varieties whenever available.
• Ensuring excellent field drainage to prevent waterlogging.
• Thorough cleaning of machinery and tools between different fields.