The disease triangle: Moisture means sclerotinia

The three points of the disease triangle are host, pathogen and environment. When it comes to sclerotinia stem rot in canola in Western Canada, the disease triangle hinges on one component: Environment.

Host: CHECK With 22 million acres of canola alone, host crops are widespread across the Prairies. Sclerotinia stem rot (white mould) also infects soybeans, sunflowers and pulse crops.

Pathogen: CHECK With a history of large canola crops (and other host crops such as soybeans and sunflowers) all across the Prairies and with fairly regular incidence rates of sclerotinia stem rot (sometimes very high), the pathogen is everywhere. With moisture, resting sclerotia will germinate, produce apothecia and release spores in high numbers.

Environment: ????? If conditions are moist from three weeks before flowering and through flowering, apothecia will be present and release spores at the right time for infection. If crop canopy is thick, yield potential is high and moisture (humidity if not rain) continues, infection could be very high. However, if conditions are dry and crops are thin, infection could be very low. When it comes to sclerotinia stem rot infection (and the fungicide decision), environment is everything.

Further reading:

Sclerotinia risk assessment and fungicide planning
Sclerotinia stem rot management