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ISHS Acta Horticulturae 1207: V International Symposium on Tomato Diseases: Perspectives and Future Directions in Tomato Protection

Evaluation of biopesticides and biorationals on bacterial canker and bacterial spot disease levels in tomato fresh-market production in North Carolina

Author:   F.J. Louws
Keywords:   Clavibacter, Xanthomonas, tomato, disease control, late blight
DOI:   10.17660/ActaHortic.2018.1207.33
The dynamics of bacterial speck (Pseudomonas syringae pv. tomato; Pst), bacterial canker (Clavibacter michiganesis subsp. michiganesis; Cmm) and bacterial spot (Bsp; Xanthomonas) have shifted over time in fresh-market tomato production systems in North Carolina. Cmm occurs sporadically on farms and, in most cases, the symptoms are restricted to hotspots in fields that show the “secondary” phase of the disease, resulting in “firing” of the foliage and “bird's eye” fruit spot. Recently, systemic infections and plant death have been uncommon. Twelve or more years ago, Pst was the primary foliar bacterial pathogen. Recently, however, Bsp has become widely distributed and can cause extensive defoliation, although the fruit spot phase is uncommon. Evidence suggests that, around 2000, the primary pathogen was Xanthomonas euvesicatoria, but it has since shifted to Xanthomonas perforans. Bsp sprays include the use of streptomycin on transplants followed by copper tank-mixed with mancozeb and rotated with acibenzolar-S-methyl (Actigard 50WG) in the field, but control is inadequate under conditions that favor disease progress. A replicated field study evaluated 12 treatments, including several biopesticides and biorationals. Cmm-infested plants were planted within six plant plots to allow natural spread. Cmm damage to foliage ranged from 2 to 20%. Plots sprayed with water only and inoculated with Cmm tended to have the largest area-under-the-disease-progress curve (AUDPC) values; plots sprayed with water and not inoculated had the lowest, and all other treatments tended to fall in between. Natural inoculum of Xanthomonas overtook the plots by the end of the season. Bsp severity values showed differences between treatments, with the non-treated (water only) plots tending toward the greatest levels of disease and Cease (Bacillus strain) + MilStop (potassium bicarbonate), Double Nickel (Bacillus strain) and Cueva (copper) providing the best control. When disease pressure was high, none of the treatments conferred sufficient control. Additional work is needed to design integrated pest management (IPM) programs that mitigate high Bsp pressure.

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