Evaluation of Seed, In-Furrow, and Soil Treatments for the Management of Powdery Scab ( Spongospora subterranea f. sp. subterranea ) of Potato in New Brunswick, Canada

Two field experiments were conducted in New Brunswick, Canada, in 2020 and 2021 to test the efficacy of various fungicides, soil amendments, and plant byproducts in managing powdery scab ( Spongospora subterranea f. sp. subterranea) of potato ( Solanum tuberosum) in previously infested potato fields. Disease-free ‘Calwhite’ potato seed was used. In 2020, 14 treatments were used, including fungicides, biostimulants, and fertilizers. Treatments did not affect emergence or vigor. Fluazinam single dose (1×) and double dose (2×), mancozeb single dose (1×), or cyazofamid in-furrow significantly reduced the percentage of diseased tuber weight (%DTW) by 70.3, 62.6, 54.9, or 75.1% and increased marketable yield (MY) by 22.1, 26.5, 41.6, and 30.5%, respectively. Boron significantly reduced %DTW by 66.9% and increased MY by 23.9%. The trial was repeated in 2021 using nine treatments. In-furrow fluazinam, mancozeb, or cyazofamid reduced %DTW by 43.7, 39.7, or 54.4% and increased MY by 75.5, 57.0, and 65.9%, respectively. Boron also significantly increased MY. The second-year trial confirmed that in-furrow application of fluazinam, mancozeb, or cyazofamid is more suitable in managing powdery scab and increasing MY in disease-infested fields, and boron soil treatment is a promising alternative for chemical treatments. The difference in MY is solely due to the powdery scab disease severity.