Barbara Bowen

Phosphite is of major importance in controlling root disease caused by Phytophthora cinnamomi. It acts both directly and indirectly on the pathogen. In order to maximise the efficacy of phosphite we need to understand how the physiological status of the plant at the time of phosphite application affects control. The physiological status of plants is not constant but varies over time depending on developmental gene expression (e.g. leaf phenology, flowering/fruiting and senescence) and interactions with the environment (e.g. temperature, moisture, light, fire, nutrients and other biota). In Mediterranean environments in particular, plants experience stresses due to extremes in water availability and the incidence of wild fire is high. Furthermore, individuals and species of plants are not in synchrony due to differences in recruitment, ontogeny, longevity and rest periods. Therefore, from a management perspective when considering all of these stresses native plant communities are subjected to, it is critical to know when to apply phosphite to ensure optimal disease control. We examined each of the key environmental stresses (water excess, water deficit, fire and flowering) independently, on the efficacy of phosphite to control disease.