نبذة مختصرة : The olive moth, Prays oleae (Bernard) (Lepidoptera: Yponomeutidae), is one of the most destructive pests of olive groves in the Mediterranean basin. In recent years, the interest in evaluating the economic importance of P. oleae has been increasing, being loss assessment essential to the development of integrated pest management programs (IPM). Reliable economic thresholds for the pest are associated to any IPM practice, since enables the growers to reduce the input of pesticides and even target their use, when necessary. The purpose of this study was to establish economic thresholds against the fruit generation of P. oleae (Bern.) in Trás-os-Montes region (north-eastern Portugal), where the olive moth is a key pest of olive (Bento et al., 1997; Bento, 1999). The study was carried out in olives of the oil-producing variety "Cobrançosa, Verdial Transmontana and Madural", grown on non irrigated conditions and without pesticide treatments for several years. Data of Cobrançosa variety were recorded every year from 1993 to 2006. Olive infestation was determined in 25 fruits taken from 25 trees selected at random in orchard, weekly collected, from the time of fruit setting until the end of the egg-laying period. Crop losses due to preharvest fruit drop were evaluated on 25 olive trees from fruit setting until harvest. A mathematical model is developed which aims to establish the economic thresholds for the olive moth in Portugal. The model takes into account several factors such as: cost and efficacy of spraying, environmental impact, expected yield, price and crop losses.
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