User-friendly methodology for risk assessment of Tetranychus urticae (Acari: Tetranychidae) in greenhouse rose production
Abstract: Two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae) is one of the most polyphagous arthropod herbivores and is a major pest in grenhouse roses. For a better control a method for estimating the risk of T. urticae in grenhouse roses is needed. An assay was carried in a grenhouse located in Northwest of Portugal, 138 terminal leaflets were hand-picked from the Rosa hybrida cv. “White Naomi” and cv. “Red Naomi” and observed at stereomicroscope. A scale was proposed and validated with 8040 field observations. The methodoly proposed consists in the observation of 20 terminal leaflets from maintenance layer, randomly chosen in each homogeneous greenhouse area, and a quick on site scoring of each leaflet in 0, 1 or 2, ((0) beeing pest absent, (1) the presence of 1 or 2 mobile forms or eggs and (2) the presence of 3 or more mobile forms or eggs). The comparation beetween the mean calculated and the proposed economic threshold (ET) = 1 defines the decision making in control. An easy to use and reliable methodoly and scale are proposed for T. urticae risk assessement in greenhouse roses.