BIOLOGICAL AND MICROBIAL CONTROL Plant-Related Factors Influence the Effectiveness of Neoseiulus fallacis (Acari: Phytoseiidae), a Biological Control Agent of Spider Mites on Landscape Ornamental Plants

The predatory mite Neoseiulus fallacis (Garman) was evaluated as a biological control agent of herbivorous mites on outdoor-grown ornamental landscape plants. To elucidate factors that may affect predator efÞciency, replicated tests were conducted on 30 ornamental plant cultivars that varied in relationship to their generalized morphology (e.g., conifers, shade trees, evergreen shrubs, deciduous shrubs, and herbaceous perennials), production method (potted or Þeld grown), canopy density, and the prey species present on each. Plant morphological grouping and foliar density appeared to be the most inßuential factors in predicting successful biological control. Among plant morphological groups, N. fallacis was most effective on shrubs and herbaceous perennials and less effective on conifers and shade trees. N. fallacis was equally effective at controlling spider mites on containerized(potted)andÞeldgrownplants, and therewasnodifference incontrolofmitesonplants with Tetranychus spp. versus those with Oligonychus or Schizotetranychus spp. Moderate to unsuccessful control of spider mites by N. fallacis occurred mostly on tall, vertical plants with sparse canopies. Acceptable spider mite control occurred in four large-scale releases of N. fallacis into production plantings of Abies procera, Thuja occidentalis ÔEmeraldÕ, Malus rootstock, and Viburnum plicatum ÔNewportÕ. These data suggest that N. fallacis can be an effective biological control agent of multiple spidermite species in a range of low-growing and selected higher growing ornamental plants.