Abstract
The effect of two types of granular organic fertilizers, fish meal pellet and rape seed meal pellet, on the damage caused to spinach by Tyrophagus similis Volgin(Acari: Acaridae)was investigated. From April to July 2013, spinach was cultivated three times in greenhouses in Hokkaido. The area was divided into 3.24 m2 plots, and the fertilizers were applied at the rate of 40 kg/10 a in the early two-leaf stage of spinach. The mites were confirmed to adhere to the fertilizer pellets immediately after they were applied until harvest time, with the likelihood of this tendency increasing with each day after application. The mites were rarely captured in acarid bait traps from immediately after fertilizers were applied to just before harvest in the treated plots, although they were captured in high densities in untreated plots. The first evidence of damage to spinach in each treated plot was recorded after 1 to 2 weeks in untreated plots. The extent of damage was much lower in the treated plots at harvest time. These results suggested that T. similis preferred organic fertilizers to a greater extent than spinach and that the use of organic fertilizers prevented the mites’ infestation on spinach. In addition, other insect pest species, such as seed-corn maggot(Delia platura(Meigen)), were absent from each treated plot.
