From 2003 to 2015, 66 products representing 59 active ingredients were tested through the IR-4 Program as drench or foliar applications against nine Phytophthora species causing root rots and stem/leaf blights. Phytophthora species tested included: P. cactorum, P. cinnamomi, P. citricola, P. cryptogea, P. dreschleri, P. nicotianae/parasitica, P. palmivora, P. plurivora, P. ramorum, P. syringae, and P. tropicalis. Control of Phytophthora cinnamomi root rot was achieved primarily with drench applications onto azaleas. When this pathogen was tested on rhododendrons, the data were either inconclusive or the products did not perform as well as on azaleas with the exception of Magellan and Fenamidone. For Phytophthora dreschleri root rot, the good to excellent efficacy was achieved with several products including BioPhos, Segway, Stature DM, and Terrazole. For Phytophthora nicotianae, consistent efficacy across crops was difficult to achieve, but the best performers included Adorn, Aliette, Alude, Biophos, Fenamidone, Insignia, Micora Segway, Stature DM, Subdue MAXX, and Vital. The best control of Phytophthora citricola blight was achieved with foliar applications of the phosphorus acid generators Aliette, Biophos and Magellan. For Phytophthora ramorum blights, Subdue MAXX provided the most consistent control. Adorn, Fenamidone, Insignia, Segway, and Stature also provided good control. For Phytophthora tropicalis, the best control was achieved with Adorn and Stature. Micora and Segovis provided effective control of Phyotopthora plurivora in two rhododendron experiments.
