Economic trade-offs with canola-based crop rotations in the presence of clubroot (Plasmodiophora brassicae)

Clubroot (Plasmodiophora brassicae) is a soil-borne disease of Brassica crops, including canola (Brassica napus) on the Canadian Prairies. Intensive canola cropping can expedite disease severity, leading to escalated yield loss and lost profits. This study examined the long-term economic implications for two canola-based crop rotations in the presence of clubroot in the Edmonton, Alberta area. Clubroot disease severity was modelled over time to incorporate rotation and clubroot resistance effects on canola yield. The first part of the analysis compared annual returns from hard red spring wheat production to canola with different disease severity index levels. Clubroot disease severity index levels of 35% or more resulted in wheat having higher returns than canola. The second part of the analysis used a bio-economic model with a clubroot sub-model to compare crop rotations. The two-year rotation of canola-wheat was optimal if clubroot disease was low, otherwise canola-wheat-field pea had higher long-term net returns. With a susceptible cultivar, annual net returns averaged $140 ha-1yr-1 higher for the three-year than the two-year rotation. When a clubroot resistant cultivar was introduced, but resistance broke over time, the three-year rotation had higher annual returns of $56ha-1yr-1. Pre-emptive and early use of more break-years between canola crops was critical whether growing susceptible or clubroot resistant cultivars to maintain profitable canola production over time. This result is consistent with agronomic recommendations for canola production.