Spider mite is the most concerned pest in apple production. This study compared and analyzed the historical changes of two mite pests, Tetranychus urticae koch and Panonychus ulmi (Koch) in 16-30 representative apple orchards in the major apple production area; Gyeongnam, Gyeongbuk, and Jeonbuk province of Korea from 1992 to 2007. Monthly sampling of 100 leaves per orchard provided the basic data of population density of two mite species. Among those orchards, chemical spray history was also analyzed from four orchards, which could be representatives of IPM practitioners.
It was found that overall population densities of T. urticae were higher than those of P. ulmi for 16 years. Before 2000, T. urticae was dominant over P. ulmi in most orchards. However since 2000, P. ulmi have occurred more than or as much as T. urticae.. Moreover, although there was large fluctuation of occurrences of two mite species over the years and localities, spider mite pressure appeared to decrease, in general. It seemed to relate the timing of ground cover management with pheromone-based IPM implementation nationwide from late 90s.
Panonychus ulmi appeared to rise in April and July in general, fall in August, and go up again in the late season; September-October, while T. urticae appeared to begin to rise in June with July or August peak and sometime with late season second peak in October.
Application frequency of acaricide has been dropped from four times in the late 1990s to 2.5 times in the late 2000s.

• Kyung Hee Choi(Apple Experiment Station, National Horticulture Research Institute, RDA)
• Soon Won Lee(Apple Experiment Station, National Horticulture Research Institute, RDA)
• Dong Hyunk Lee(Apple Experiment Station, National Horticulture Research Institute, RDA)
• Dong Ah Kim(Apple Experiment Station, National Horticulture Research Institute, RDA)
• Chuleui Jung(School of bioresource Sciences, Andong National University)