Fosetyl-aluminium injection controls root rot disease affecting Quercus suber in southern Spain

Abstract

In Spain, natural and managed cork oak woodlands are severely affected by decline caused by the root rot oomycetes Phytophthora cinnamomi and Pythium spiculum. The need for environmental-friendly disease management makes the use of resistance inducers a suitable option. As the use of phosphite is prohibited in Spain, trunk injections of fosetyl-aluminium were tested in a seminatural cork oak woodland (dehesa). Sixty cork oaks in three different defoliation classes (asymptomatic, slight, and moderate defoliation) were selected for fosetyl- aluminium or control (water) trunk injections, and periodically checked for defoliation and presence of both pathogens in roots and rhizosphere soil. Three years after treatments, fosetyl-aluminium injection significantly decreased defoliation in treated cork oaks in comparison with water-injected controls, regardless of the initial defoliation class considered. Changes in inoculum density in the rhizosphere or presence of the two pathogens in roots were not significantly dependent on treatment. However, a trend to a lower presence of pathogens in roots of treated oaks was observed with increasing soil inoculum densities. Fosetyl-aluminium, a phosphonate fungicide registered in the European Union, was experimentally proved to protect cork oaks against root rot caused by P. cinnamomi and Py. spiculum, even exhibiting a therapeutic effect on preexisting infections. This effective measure can therefore be used to fight against this highly destructive disease in seminatural woodlands and in protected natural ecosystems.