Inhibition of Downy Mildew, Powdery Mildew and Black Rot and Differential Expression of Defence‐Related Genes in Conventional and Non‐Conventional Treatments

Climate change makes the development and survival of grapevine pathogens increasingly unpredictable, posing challenges for winegrowers. This study evaluated the ability of plant extracts to prevent Plasmopara viticola, Erysiphe necator and Guignardia bidwellii in order to reduce the use of chemical control. A trial was conducted during two consecutive growing seasons in an experimental vineyard of the University of Trás-os Montes e Alto Douro, including four foliar treatments: nettle extract (NE), Japanese knotweed extract (JKE), conventional treatment (CT) and a water control (C). Disease incidence and severity were assessed in leaves and berries, together with the expression of six defence-related genes. NE and JKE showed partial effectiveness in reducing disease severity in leaves, in some cases approaching the performance of CT, but their impact on berry infections was limited. Both extracts induced the activation of several defence-related genes, indicating an elicitor effect that varied between years and phenological stages. The results indicate that these plant extracts may contribute to grapevine defence activation, although their direct disease control capacity, particularly in berries, remains limited. Therefore, these extracts may be more effective when incorporated into an integrated disease management programme rather than used as stand-alone treatments.