Baseline sensitivity of septoria leaf blotch to SDHI fungicides

Since recently, a new class of fungicides is available to control Septoria leaf blotch of wheat, the so-called carboxamides or SDHI. The risk of resistance development in Mycosphaerella graminicola to SDHI fungicides is estimated to be medium to high. Therefore the implementation of an anti-resistance strategy is necessary to preserve the efficacy of these fungicides. Sensitivity studies may be necessary in case field efficacy weakens. Thus, a method was established to conduct large-scale sensitivity tests in our laboratory. The sensitivity to three SDHI active substances (boscalid, bixafen and isopyrazam) of 117 Swiss M. graminicola strains was measured in vitro. These data describe the «baseline sensitivity» (initial sensitivity level prior to the introduction of the fungicides) and may be used in case of control failures to detect potential shifts in sensitivity. At the moment, to prevent resistance emergence and build up, SDHI fungicides are applied on cereals only once per crop and are used only in mixtures with partners having a different mode of action.