Copper Efficacy Field Trials for Control of Pseudomonas syringae pv. tabaci in Nicotiana tabacum Production

Abstract

Since 2015, Pseudomonas syringae pv. tabaci tox− has become the most significant foliar disease in the dark tobacco growing regions of Kentucky and Tennessee. Streptomycin sulfate, the main control mechanism that growers utilize to combat this bacterial disease, has evidence of resistance at 200 ppm. Field trials were established to evaluate the efficacy of copper-based products for control of angular leaf spot compared with streptomycin sulfate. Field trials were conducted from 2020 to 2022 at the West Farm of Murray State University in Murray, KY, to evaluate the efficacy of streptomycin sulfate, cuprous oxide, copper sulfate pentahydrate, and copper octanoate. In all years, the moderately susceptible dark tobacco variety KT D8LC was planted and inoculated with a streptomycin-sensitive isolate of P. syringae pv. tabaci. Tobacco treated with five applications of copper octanoate had a lower area under the disease progress curve (AUDPC) than tobacco treated with streptomycin sulfate in 2020 and 2022. Data analysis showed that in one of the three years, tobacco treated with cuprous oxide had a higher yield compared with tobacco treated with streptomycin sulfate. Tobacco treated with cuprous oxide had a higher quality grade index compared with streptomycin sulfate in 2020. Although no treatment eliminated this bacterial disease, copper products, particularly cuprous oxide and copper octanoate, are suitable alternatives to streptomycin sulfate for management of angular leaf spot.