Managing Colorado Potato Beetles (Coleoptera: Chrysomelidae) and European Corn Borers (Lepidoptera: Pyralidae) in Potato with Foliar Applications of Bacillus thuringiensis Berliner

Abstract

Application timing and rate combinations of Bacillus thuringiensis Berliner used for protecting Irish potato, Solanum tuberosum L., from defoliation by the Colorado potato beetle, Leptinotarsa decemlineata (Say), and stem injury by the European corn borer, Ostrinia nubilalis (Hübner), were investigated. Significant reductions in defoliation levels during bloom, populations of first-generation potato beetle adults, and the percentage of stems injured by corn borers at the end of the season in B. thuringiensis-treated potato were considered criteria for a successful management strategy. Although Colorado potato beetle infestations were managed effectively with B. thuringiensis, European corn borer populations were not reduced to a commercially 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 control. In contrast, results indicated that 1 application of B. thuringiensis 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 bloom stage. However, this strategy may not be sufficient to prevent significant levels of defoliation by first-generation potato beetle adults during post-bloom or reduce the size of this population, which will infest next season's crop. For this reason, the B. thuringiensis subsp. tenebrionis timing and rate regimen described above may be most effective in fields where the overwintering 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.