Phytophthora agathidicida is a cryptic pathogen that primarily infects kauri (Agathis australis) roots, causing kauri dieback with a very long latent period from infection to symptom expression. Current methods of pathogen detection involve collecting soil samples for baiting or DNA analysis of Phytophthora species, but confirming pathogen presence through soil testing and implementing management is typically only done on symptomatic trees. Determining infection at an earlier stage could significantly improve the management of kauri dieback. This study aimed first, to determine if P. agathidicida infection could be detected using hyperspectral and thermal imaging in potted kauri trees under glasshouse conditions. Second, it was determined whether these methods could detect the impact of foliar phosphite application for controlling disease. Leaf gas exchange, water use, and hyperspectral and thermal imaging were all used to corroborate changes in plant physiology following infection by P. agathidicida and treatment with phosphite. All physiological metrics detected disease before the end of the trial with stomatal conductance being the most sensitive. Vegetation and thermal indices could detect disease with mixed success depending on the index. Application of foliar 7.5 g/L phosphite (Foschek®) + 0.2% v/v Du-Wett® resulted in a temporary significant reduction in plant water use, stomatal conductance and photochemical reflective index that recovered in the following weeks. Glasshouse data suggest remote sensing data may be a useful tool for managing kauri dieback under field conditions. These findings will be discussed along with the extension and validation of this work in a large scale, multi-year field trial on mature kauri trees.