Chemical Efficacy Field Trials for <i>Pseudomonas syringae</i> pv. <i>tabaci</i> (Angular Leaf Spot) in <i>Nicotiana tabacum</i>

Pseudomonas syringae pv. tabaci tox – is the causal agent of angular leaf spot in dark tobacco. Since 2015, angular leaf spot has become the most significant foliar disease of dark tobacco production in Kentucky and Tennessee. Dark tobacco producers utilize streptomycin sulfate as their primary chemical control for the management of this bacterial disease. Resistance to streptomycin sulfate in P. syringae pv. tabaci isolates from dark tobacco fields in western Kentucky was first observed in 2015. Field trials were developed to evaluate the efficacy of alternative active ingredients compared with streptomycin sulfate. Field trials were conducted in 2020, 2021, and 2022 to evaluate the efficacy of streptomycin sulfate, laminarin, cuprous oxide, Reynoutria sachalinensis, peroxyacetic acid, polyoxin D zinc salt, Ulocladium oudemansii strain U3, and acibenzolar-S-methyl for control of angular leaf spot. In all trials, dark tobacco variety KT D8LC was utilized, as this tobacco variety had previously shown high susceptibility to angular leaf spot. There are no dark tobacco varieties resistant to angular leaf spot. Plots in all years were inoculated with a streptomycin sulfate-sensitive isolate of P. syringae pv. tabaci. Data analysis showed that the streptomycin sulfate performed similarly to most other treatments. No treatment completely eliminated this bacterial disease, but based on these results, cuprous oxide and U. oudemansii strain U3 are suitable for management of angular leaf spot. Implementing a spray regimen with varying active ingredients and modes of action is key in preventing pathogen resistance and decreasing the intensity of angular leaf spot.