Some of the most prominent exotic pathogens in temperate forest regions belong to the genus Phytophthora. The pathogen, which is nourished by the enzymatic destruction of living plant cells, can cause mortality in more than 150 plant species including many temperate forest trees. However, a number of studies have demonstrated ways in which Phytophthora can be directly or indirectly controlled using methods to deploy the biological elicitors Bacillus amyloliquefaciens and Trichoderma atroviride, and biochemical compounds biochar, salts of phosphorous acid, copper oxychloride, fosetyl-aluminium, metalaxyl, monoammonium phosphate, phosphite, potassium phosphonate, and urea by foliar sprays, trunk injection or bark application, and soil amendments. This systematic review has followed a rigorous literature search procedure followed by meta-analysis to identify and analyse the efficacy of existing Phytophthora treatments with an emphasis on those that induce a natural resistance in temperate trees such as phosphorous acid and phosphite based compounds. Results showed that treatments reduced Phytophthora infection symptoms compared to controls in all but one of the experiments reviewed. Trunk injections demonstrated the highest cumulative efficacy with a pooled effect size of 1.85 ± 0.56 (Hedge’s g ± 95% confidence interval). Foliar sprays had the second highest efficacy with a pooled effect size of 1.11 ± 0.28. Finally, soil amendments had the lowest cumulative efficacy with a pooled effect size of 0.61 ± 0.36. This review supports the use of treatments on trees in nurseries, urban forests, orchards and arboreta; however, success is dependent upon the application of optimal doses.