| Tomato is an economically important segment of agricultural production in the United States. Bacterial leaf spot (BLS) causes serious losses in tomato and pepper in the Midwest. Four Xanthomonas species cause BLS on these crops. In a four-year survey covering 16 counties in Ohio and one county in Michigan focused on the causal bacteria of BLS in processing tomatoes, fresh market tomatoes and peppers, a total of 240 strains were isolated, containing 169, 45, and 26 strains of X. gardneri, X. perforans, and X. euvesicatoria, respectively. The predominant species in processing and fresh market tomatoes was X. gardneri. Xanthomonas euvesicatoria was the most abundant species in peppers. Of all strains collected in this survey, 98%, 68% and 4% were insensitive to 30, 100, and 200 microg/ml copper sulfate, respectively.;Bactericides and a plant resistance activator were evaluated for efficacy in reducing BLS disease intensity in the greenhouse and field. In a greenhouse simulating a commercial seedling production environment, both acibenzolar-S-methyl and aluminum Tris O-ethyl phosphate reduced bacterial populations relative to the negative control in one of the two trials. In the second trial, lower seedling density contributed to reduced BLS severity compared to higher seedling density. In field trials, both acibenzolar-S-methyl and isothiazolone in combination with the surfactant (Activator 90) significantly reduced the yield of fruits with BLS symptoms compared to the non-treated control in one of the two years of the study. The addition of Activator 90 improved the efficacy of acibenzolar-S-methyl and copper sulfate in reducing BLS on fruit in one of two years. However, fruits from plants treated with isothiazolone plus Activator 90 exhibited more large BLS lesions in one of the years than the non-treated control. The percentage of fruits with BLS symptoms, foliar BLS severity at the end of field experiment, and area under the disease progression curve for foliar BLS were not affected by the addition of Activator 90 in either year. The addition of non-ionic surfactant to a copper-based bactericide increased the surface tenacity of copper in a controlled environment. When exposed to different humidity regimes, tomato seedlings had 4.6 times more BLS lesions with the high initial (80%) relative humidity in comparison to low initial relative humidity (30--45%). For every 24 hours of high humidity in the first 8 days post inoculation, the number of BLS lesions on seedlings increased by 10%.;The effects of colored pulsed xenon lights on suppression of BLS caused by X. gardneri were tested. Blue strobe light treatment suppressed bacterial populations on seedlings in one of two experiments. The formation of large BLS lesions on fruits in the field was lower in plants treated as seedlings with blue, amber, and red strobe light in one of two years than in plants exposed to natural light. However, BLS foliar severity was higher, relative to the control, in the plants that received inoculum indirectly and were exposed to blue light as seedlings in 2014. Blue light had the most significant impact on seedling growth, including reduced seedling height and increased dry weight compared to the control. |
