Western flower thrips (WFT), Frankliniella occidentalis (Pergande), on table grapes in the Hex River Valley wasmonitored and its seasonal occurrence was investigated over three seasons. At the start of the growing season, bluesticky traps suspended from the overhead trellising structure to hang outside and under the vine canopy yieldedsimilar WFT numbers. However, as the season progressed and vine canopies became denser, more WFT were caughton traps hanging outside the canopy in full sunlight than on traps hanging under the vine canopy. Female WFTbecame active in the vineyards after bud break and their numbers increased rapidly during flowering, peakingbetween October and January and declining rapidly thereafter. WFT were present in pre-bloom inflorescences andshoot tips before flowering, which means that monitoring should commence as soon as the first inflorescences areformed. No consistent relationship was found between economic damage at harvest and WFT numbers on stickytraps during flowering and berry set. Sticky traps should therefore only be used to determine the presence orabsence of WFT in vineyards. The trap results suggest that there could be a constant influx of thrips into vineyardsfrom alternate host plants in the surrounding area during the growing season. In vineyards with a history of WFTdamage, control measures should be considered as soon as WFT is detected in order to prevent halo spot damage
