Clubroot

Affected plants develop swollen, distorted galls on roots in place of normal root structure. Above ground, plants are often stunted and may wilt in warm or dry weather despite adequate soil moisture, because damaged roots cannot supply the plant's water needs. Poor stands often appear in patches within a field.

Resting spores in soil germinate to release zoospores that swim through soil water to infect root hairs. A secondary infection cycle within root cortical tissue produces the characteristic galls. As galls decay, they release enormous numbers of new resting spores that can persist in soil for many years even without a susceptible host.

• Resting spores can remain viable in soil for many years
• Zoospore movement through soil requires water, so moist or poorly drained soil favours infection
• Infested soil moved on equipment, footwear, or planting material can introduce the pathogen to new fields

Clubroot affects brassica crops broadly. Cabbage, broccoli, cauliflower, and kale are notable hosts, along with many other brassica vegetables and some brassica weeds that can maintain soil inoculum between susceptible crops.

• Acidic soil pH, which favours spore germination and disease development
• Persistently moist or poorly drained soil
• Short rotations with brassica crops, allowing soil spore populations to build
• Movement of infested soil on equipment, footwear, or planting material

Because clubroot spores can persist in soil for years, prevention emphasises reducing conditions that favour the pathogen and limiting its introduction and spread between fields.

• Raise soil pH toward neutral or slightly alkaline through liming where appropriate for the cropping system
• Improve field drainage where persistent moisture is a factor
• Use long rotations away from brassica hosts where clubroot has been present
• Use clubroot-resistant varieties where available, and sanitise equipment moving between fields