| Resumo: | A mathematical model is presented which aims to establish the economic thresholds for the flower generation of olive moth, Prays oleae (Bern.) in Tràs-os- Montes (north-eastern Portugal). The model is based on observations taken between 1993 and 1998, on olives of the oil variety Cobrançosa, grown under rain-fed conditions and without pesticide treatments for several years. It takes into account factors such as cost and efficacy of spraying, environmental impact, expected yield, price and crop losses. According to this model the control of the pest is justified when the percent of flower infestation is between 4.0 % and 6.0 % during the years of intermediate and high expected yields, (i.e., about 2400 kg/ha) and between 8.0 % and 11.0 % in the years of lower expected yields (i.e. approximately 1000 kg/ha) for prices usually practised in the region.
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