Efficacy of Liquid Brassica Seed Meal Formulations Against <i>Phytophthora cinnamomi</i> in Laboratory and Field Conditions in an Ink‐Diseased Cork Oak Forest

ABSTRACT Oak decline, driven by Phytophthora cinnamomi , poses a significant threat to oak forests worldwide. Biofumigation using defatted brassica seed meals has emerged as a promising biocontrol strategy within integrated pest management strategies. The efficacy of biofumigation by Brassica carinata defatted seed meal in suppressing several soil‐borne pathogens, including oomycetes, has been demonstrated by several studies. However, specific studies employing different formulations and doses are needed to support the release of a standard protocol of use. In this study, the efficacy of two commercial products based on B. carinata against P . cinnamomi and the impact on the soil microbial community were explored in mesocosm and open‐field experiments conducted in an ink‐diseased cork oak forest in central Italy. Dry pellets and a liquid formulation were first tested in a mesocosm in natural soil with P . cinnamomi inoculum, demonstrating the greater efficacy of the latter. Further experiments carried out in mesocosms and open fields showed that the liquid formulation at a final concentration of 2% of liquid concentrate of defatted seed meal of B. carinata in water was able to completely kill the inoculum down to a depth of 15 cm. At the same concentration, the product effectively protected cork oak seedlings in artificial inoculation experiments. These results underscore the potential of biofumigation as a sustainable alternative to chemical fumigation, promoting its integration into comprehensive disease management strategies for sustainable forestry practices.