A Tentative Economic Injury Level for Greenhouse Whitefly on Cucumber Plants in the Protective Cultivation

This study was conducted to estimate the economic injury level (EIL) and economic threshold (ET) of the greenhouse whitefly (Trialeurodes vaporariorum) on cucumber plants in greenhouse cultivation. The growth, damage and yield of cucumber plants caused by T. vaporariorum were investigated after introduction of the adults at different densities (0, 5, 10, 20, 40, 80, and 160 adults per plant). The rate of damaged leaves was not significantly different among the treatment plots with different initial densities at 32 d after the adult introduction, while it significantly increased according to increasing initial density at 56 d and 84 d after adult introduction. The total yield of cucumber was 22.5, 19.5, 11.3, 9.8, 8.2, 5.2, and 4.6 kg per 20 plants in T. vaporariorum introduced plots of 0, 10, 20, 40, 80, and 160 adults per plant, respectively. The fruit damage significantly occurred from 63d after T. vaporariorum adult introduction, and it reached 0, 4.1, 7.5, 10.6, 18.2, 26.7, and 38.5% at harvest (84 d after adult introduction) in the above plots, respectively. The relationship between the initial adult density and % fruit damage at harvest was well described by a nonlinear logistic equation. Using the estimated equation and an empirical gain threshold 5%, EIL was estimated at 6.2 adults per plant. Also, ET was calculated at 80% of EIL: 5.0 adults per plant. Until a more elaborate EIL-model is developed, the present result may be used tentatively for T. vaporariorum management in cucumber fields.