Farm typology to manage sustainable blackleg resistance in oilseed rape

Blackleg—Leptosphaeria maculans—is a major worldwide pest for oilseed rape. Blackleg is an airborne pathogen spreading over several kilometres and surviving for at least 3–5 years on crop residues. In oilseed rape, the classical control strategy against blackleg is varietal resistance. However, genetic diversity is decreasing in agricultural crops. Moreover, at the farm level, management of oilseed resistance to blackleg must be adapted to take into account specific farm household objectives and organisation. Therefore, the different types of oilseed management should be identified. Here, we built a typology of oilseed rape management focusing on blackleg management. We used a methodology based on expert knowledge to analyse 32 farms of three French regions. Our results show that eight types of oilseed rape management were identified and can be discriminated according to the risk of blackleg resistance breakdown. We thus identified three categories, high, low, and medium risks. High risk management types have both a low level of oilseed rape management flexibility and a high level of inputs. Low risk systems are systems where oilseed rape is only a minor part of farmer sales and where inputs are minimised. Medium risk systems are systems where oilseed rape is integrated in the rotation, and where input use is optimised by taking into account the short rotation and the expected revenue. Our typology therefore allows to define practices not only on classical agronomic criteria but also on crop sales part in the farm and on input levels