The effects of overhead irrigation and leaf structure on foliar microarthropods including Neoseiulus cucumeris

Neoseiulus cucumeris is a foliar predatory mite of immature thrips used in greenhouses.  We conducted two trials assessing the effects of leaf structure and irrigation events on populations of mites and thrips. In our first trial, N. cucumeris was applied in a sprinkle formulation containing bran flakes, yeast, mold mites, and the predatory mite to basil and rosemary plants.  Mites were allowed to disperse for two hours before overhead irrigation was applied. Sampling intervals were before mite application, before the irrigation event, immediately after the irrigation event, and 24 hours after the irrigation event.  In the second trial, basil, cilantro, oregano and tomato plants were used.  N. cucumeris was applied and dispersed overnight before watering.  Sampling intervals were the same as before with the addition of six hours after the irrigation event. Plants were selected based upon their differences in leaf structure, simple versus compound, and the presence or absence of hairs and trichomes.  In the first trial, mold mites were negatively affected by watering; however, predatory mites were not.  In the second trial, populations of mold mites on basil and cilantro were reduced, but not the populations on oregano or tomato.  Predatory mites were not affected by watering on cilantro and tomato; however, predatory mites on basil and oregano were.  Overhead irrigation had little to no effect on thrips populations in both trials. We conclude that overhead irrigation may have a deleterious effect on microarthropods within the plant canopy depending upon leaf structure.