CHEMICAL CONTROL OF BLACK SHANK (PHYTOPHTHORA NICOTIANAE) IN STRIP-TILLAGE DARK FIRE-CURED TOBACCO

Abstract

Black shank, a soil-borne disease caused by Phytophthora nicotianae, is one of the most devastating oomycetes affecting dark tobacco worldwide. Field trials were conducted in 2018 and 2022 at an established black shank site near Hopkinsville, KY, to evaluate the efficacy of mefenoxam, fluopicolide, and oxathiapiprolin for management of black shank in dark fire-cured tobacco. Black shank field trials at this location have been conducted each year since 2006. KT D6LC, a dark-fired cultivar with moderate resistance to race 0 and race 1 black shank, was used in 2018 and 2022. Black shank infection was much greater in 2022, resulting in greater stand and yield loss in 2022 compared to 2018. Rainfall amount and timing differences between the 2 years likely contributed to these differences in final stand and yield. Final stand and total yield ranged from 80.7 to 99.3% and 2,374 to 2,882 kg ha−1, respectively, in 2018, and from 10.3 to 81.8% and 238 to 2,637 kg ha−1, respectively, in 2022. In both years, all oomyceticide treatments increased final stand and yield compared to untreated tobacco. In 2018, highest final stand came from tobacco that received mefenoxam or oxathiapiprolin plus mefenoxam at transplanting alone or followed by fluopicolide and mefenoxam after transplanting, or fluopicolide followed by mefenoxam after transplanting. Total yield was similar for tobacco treated with any oomyceticide treatment and higher than the yield of untreated tobacco in 2018. In 2022, tobacco treated with oxathiapiprolin plus mefenoxam in transplant water either alone or followed by fluopicolide and mefenoxam had significantly higher final stand and yield than all other treatments. Across both years, it was evident that oomyceticide applications made in transplant water, particularly oxathiapiprolin plus mefenoxam, had the greatest impact on black shank management in dark fire-cured tobacco.