Economic Injury Levels and Control Threshold of Tetranychus kanzawai Kishida(Acari, Tetranychidae) Infesting Korean Black Raspberry (Rubus coreanus Miquel)

摘要

Economic injury levels (EILs) and economic control threshold (ET) were estimated for the Tea red spider mite, Tetranychus kanzawai Kishida(Acari, Tetranychidae) in Rubus coreanus Miquel. T. kanzawai density increased until the early-July and thereafter decreased in all plots except the non-innoculation plot where initial density of the mite were different each 0,5,10,20 and 40 adults per plant branch on May 7 in 2008. And the occurrence of the densities were increased higher innoculated density thandifferent innoculation density. The yield was decreased with increasing initial mite density and thereby the rates of yield loss was increased with increasing initial mite density. And T. kanzawai occurrence density, yields and the rates of yield loss, where initial density of the mite were different each 0,2,5,10 and 20 adults per plant branch on May 8 in 2009 were similar tendency to 2008 year results. The relationship between initial T. kanzawai densities and the yield losses was well described by alinear regression, Y = 0.6545X + 3.0425 (R~2 = 0.93) in 2008, Y = 0.903IX + 2.0899(R~2 = 0.96) in 2009. Based on the relationship, the number of adults per plant branch(EILs) which can cause 5% loss of yield was estimated to be approximately 3.0 in 2008and 3.2 in 2009. And the ET was estimated to be approximately 2.4 in 2008 and 2.6 in 2009. The relationship between initial T. kanzawai densities and occurrence density of mid-May considering the best spray timing against T. kanzawai was well described by a linear regression, Y = 0.471X + 2.495(R~2 = 0.95) in 2008, Y = 0.9938X + 3.1858(R~2 = 0.96) in 2009. Based on the relationship, the number of adults per leaf(ET) in mid-May which can cause 5% loss of yield was estimated to be approximately 3.6 in 2008 and 5.8 in 2009.