Clubroot management in oilseed rape: field factors
Maintaining a relatively high soil pH (>7), addressing poor field drainage, managing levels of common clubroot hosts and preventing spread of the disease (via movement of infected soil) are among the most influential management strategies.
Maintain drainage to reduce clubroot spread
Clubroot zoospores move through soil water. Wet soils – particularly compacted, poorly drained soils and flood-prone fields – are associated with increased clubroot risk, especially if autumn soil temperatures are warm (above 15°C). Therefore, maintain fields in a well-drained state to reduce clubroot risk and provide other benefits, such as improved land workability.
Limit movement of infected soil and organic material
In addition to water, movement of infected soil and organic material is a major cause of clubroot introduction and spread, both within and between fields. On average, farm equipment transfers 250 kg of soil, most of which is deposited close to gateways and field entrances. Ensure farm staff and contractors follow good hygiene protocols and strict biosecurity procedures. Plan machinery movements to avoid travel from infested to clean fields. Restrict access to severely infested fields. On rented land, ensure tenants understand and manage risks in the same manner as farmer-owned land.
Where non-agricultural personnel need to access land, ensure they have sufficient biosecurity awareness, as contamination risks can be relatively high. For example, civil infrastructure projects can involve a high level of machinery movement. In such situations, additional hygiene measures may be necessary, such as hardstanding and wash-down facilities for vehicles and machinery.
Infected animal manures, composts, green mulches and straw can also introduce spores. It is important to understand the infection risk associated with these materials. Avoid the movement of feed swedes and turnips onto clean land. Risk associated with digestate use is low, particularly if it is compliant with PAS100 or PAS110 standards. However, take extra care when spreading high volumes.
Keep soil above pH 7 to decrease clubroot severity
Crops grown in acidic soils (lower pH numbers) are at greater risk of developing severe symptoms. Check soil pH routinely, particularly before establishing a susceptible crop. Aim to maintain the pH to above 7; even small increases (0.5–1 pH units) can decrease clubroot severity. Agricultural lime products, which are associated with a spike in pH and available calcium at drilling, can significantly reduce clubroot infection. High doses of lime (applied at 8 t/ha) can reduce clubroot severity by 25%.
As boron also has some activity against clubroot, correct any deficiencies in the soil.
Control clubroot-hosting weeds and volunteers
Cruciferous weeds, such as charlock and shepherd’s purse, are common hosts to clubroot, along with volunteer oilseed rape. Consequently, manage these weeds within and between susceptible crops. Early weed control (7–14 days post emergence), by either herbicide application or shallow disking, reduces the number of resting spores in the soil.
Clubroot hosts include field weeds, such as shepherd’s-purse