Managing Colorado potato beetles (Coleoptera : Chrysomelidae) and Europeancorn borers (Lepidoptera : Pyralidae) in potato with foliar applications of Bacillus thuringiensis Berliner

Application timing and rate combinations of Bacillus thuringiensis Berliner used for protecting Irish potato, Solanum tuberosum L., from defoliation b y the Colorado potato beetle, Leptinotarsa decemlineata (Say), and stem inj ury by the European corn borer, Ostrinia nubilalis (Hubner), were investiga ted. Significant reductions in defoliation levels during bloom, populations of first-generation potato beetle adults, and the percentage of stems inju red by corn borers at the end of the season in B. thuringiensis-treated pot ato were considered criteria for a successful management strategy. Although Colorado potato beetle infestations were managed effectively with B. thuri ngiensis, European corn borer populations were not reduced to a commerciall y acceptable level. In each of 3 yrs, neither an increase in the number of applications (from 1 to 4) nor an increase in rate (from 0.9 to 3.8 liters/ ha) of B. thuringiensis subsp. kurstaki improved the level of corn borer co ntrol. In contrast, results indicated that 1 application of B. thuringiensi s subsp. tenebrionis, timed when there was >1 large potato beetle larva per stem, using a 4.7 liters/ha rate protected the potato crop during the bloo m stage. However, this strategy may not be sufficient to prevent significan t revels of defoliation by first-generation potato beetle adults during pos t-bloom or reduce the size of this population, which will infest next seaso n's crop. For this reason, the B. thuringiensis subsp. tenebrionis timing a nd rate regimen described above may be most effective in fields where the o verwintering potato beetle population is predicted to be low to moderate (e .g., <1 adult per 5 stems), whereas two applications may be most effective in fields where densities are greater.