Mite population and damage caused by broad mites (Polyphagotarsonemus latus [Banks]) infesting bell pepper (capsicum annuum L.) at different seedling developmental stages

Abstract

Because of their small size, broad mites are unnoticeable until they cause serious damage to apical leaves in pepper seedlings. Changes in broad mite population and seedling damage over time were measured after artificial mite infestations of seedlings with unfolded cotyledons, or with unfolded two, or four true leaves. With infestations occurring at these seedling developmental stages, symptoms of elongation and curling of apical leaves were observed five days after infestation. The mite populations first increased exponentially as days after seeding (DAS) increased and populations developed more rapidly in older seedlings that were infested. At 38 DAS (transplanting age, with 6 leaves unfolded in uninfested seedlings), seedling damage was greater in those infested at younger developmental stages. Mite population in seedlings infested at two and four leaves were still increasing at 38 DAS. Damage increased more rapidly with increased cumulative mite-days in seedlings infested at the cotyledonary stage. The relative growth loss caused by one mite-day was generally greatest shortly after infestation occurred. At 38 DAS, cotyledonary-infested and 2-leaf-infested seedlings showed necrosis in cotyledons and leaves while in 4-leaf-infested seedlings, symptoms of mite damage were just starting to be noticeable. This may indicate that transplants with no symptoms, which are a potential source of infestation in greenhouse-grown crops, become infested at the end of the transplant production cycle. Ongoing research is being conducted to evaluate the effectiveness of broad mite control using biological control at different seedling developmental stages and under different temperatures.