Seasonal dynamics of economic injury levels for Tetranychus urticae Koch (Acari, Tetranychidae) on Cucumis sativus L.

Abstract

: Economic injury level (EIL) for Tetranychus urticae Koch on glasshouse cucumbers was established in two ways: EILs based on the number of T. urticae introduced to cucumber early in the growing season and EILs based on mite density and feeding durations (i.e. cumulative mite-days) in each of four growing seasons. The relationship between yield loss and T. urticae infestation level varied among four growing seasons. One mite introduced to cucumber early in the growing season could reduce the cucumber yield by 5.03, 3.20, 1.12 and 2.86 g per plant in spring, summer, autumn and winter, respectively. One mite-day (i.e. one mite feeding in a day) reduced cucumber yield by 0.0123, 0.0074, 0.0035 and 0.0073 g per plant in spring, summer, autumn and winter, respectively. When the seasonal dynamics of market values of cucumber was considered, EILs were the lowest in spring and the highest in autumn. When four seasonal data were combined, EILs can be calculated as EIL = C/(0.00276 × K) for the number of T. urticae introduced early in the growing season and EIL = C/(6.8342 × 10−6 × K) for cumulative mite-days, where K is efficacy of control measure and C the management cost. This study demonstrated the seasonal dynamics of EILs for T. urticae on glasshouse cucumbers, suggesting that decision making for T. urticae management on cucumber needs to be seasonally different under the glasshouse condition.