Eur. j. plant pathol. Eur. j. plant pathol. Potential control of forest diseases by solutions of chitosan oligomers, propolis and nanosilver Silva-Castro I. Martín-García J. Diez J.J. Flores-Pacheco J.A. Martín-Gil J. Martín-Ramos P. Universidad de Zaragoza 2018 research-article