Author ORCID Identifier
Year of Publication
Doctor of Philosophy (PhD)
Agriculture, Food and Environment
Plant and Soil Sciences
Dr. William A. Bailey
Dr. Kiersten Wise
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 in dark tobacco production in Kentucky and Tennessee. Dark tobacco producers utilize one main tool, streptomycin sulfate, 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 spray trials were developed to evaluate the efficacy of alternative active ingredients compared to the grower’s standard, streptomycin sulfate. Two separate field trials were conducted in 2020, 2021, and 2022 to evaluate the efficacy of 10 different chemical control options for the management of angular leaf spot. The first field trial investigated streptomycin sulfate, laminarin, cuprous oxide, Reynoutria sachalinensis, peroxyacetic acid, polyoxin D zinc salt, Ulocladium oudemansii strain U3, and acibenzolar-S-methyl for the management of angular leaf spot. The second field trial was established to evaluate the efficacy of streptomycin sulfate, cuprous oxide, copper sulfate pentahydrate, and copper octanoate for management of angular leaf spot. In all trials and years, dark tobacco variety KT D8LC was utilized, as this tobacco variety had previously shown 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 to ensure disease pressure.
Field trials that evaluated streptomycin sulfate, laminarin, cuprous oxide, Reynoutria sachalinensis, peroxyacetic acid, polyoxin D zinc salt, Ulocladium oudemansii strain U3, and acibenzolar-S-methyl, data analysis showed that the streptomycin sulfate performed similarly to the untreated control in most trials. No treatment eliminated this bacterial disease. Untreated tobacco, tobacco treated with polyoxin D zinc salt or peroxyacetic acid had significantly higher area under the disease progress curve than other treatments during the three-year study. No significant yield differences were observed in 2020 for area under the disease progress curve. In 2022, there were significant differences in yield. Tobacco treated with cuprous oxide followed by Reynoutria sachalinensis and the recommended spray regimen had significantly higher yields compared to 10 of the remaining 12 treatments. 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.
Field trials that evaluated the efficacy of streptomycin sulfate, cuprous oxide, copper sulfate pentahydrate, and copper octanoate data analysis showed that in two of the three years, tobacco treated with cuprous oxide had numerically higher yields compared to tobacco treated with streptomycin sulfate. In 2021 and 2022, tobacco treated with cuprous oxide also had numerically higher quality grade index compared to streptomycin sulfate, and in 2020, these differences were significant.
An observational study was conducted in 2020, 2021, and 2022 to evaluate possible correlations between grower management practices, environmental factors, and angular leaf spot. Ninety fields were monitored in this three-year study. Fields were located in seven counties in Western Kentucky and northwestern Tennessee. Growers were not asked to implement new practices or change any current practices in their management program. Four fields were confirmed to have ALS in 2020, eight fields were confirmed in 2021, and four fields were confirmed in 2022. Correlations occurred between angular leaf spot presence and three nutrients found in plant tissue: phosphorus, boron, and copper; and three nutrients found in soil: sulfur, manganese, and copper. An increased probability of angular leaf spot was also found to occur if the average temperature increases by 1°C . With one degree C increase in average air temperature, the chance of angular leaf spot being detected increases by approximately 47%.
Further research needs to be conducted in years with higher frequencies of angular leaf spot to make grower recommendations regarding nutrient recommendations. Increasing frequency of fields containing angular leaf spot are needed to make further correlations between environmental and management factors.
Digital Object Identifier (DOI)
Webb, Andrea Brooke, "EVALUATION OF CHEMICAL CONTROL OPTIONS, ENVIRONMENTAL FACTORS, AND MANAGEMENT PRACTICES ASSOCIATED WITH ANGULAR LEAF SPOT (PSEUDOMONAS SYRINGAE PV. TABACI)" (2023). Theses and Dissertations--Plant and Soil Sciences. 164.