The olive tree (Olea europea L.) is the most important fruit species of the Slovenian Istria where the olive tree cultivation has a long lasting tradition. The intensive olive tree cultivation in Slovenia has been reborn after 1991 when the old olive plantations have been renewed. Today the olive tree is the second most important fruit species in Slovenia as it covers 1242 ha, 242,55 ha of which are cultivated in the organic way. The biggest concern to the olive tree plantators are the diseases and pests, the most important one being the olive fruit fly (Bactrocera oleae [Gmelin]). The latter can cause up to 90 % of reduction in the yield of olives when the weather conditions are appropriate and when there is no defence against it. When using the integrated and organic farming methods the numbers of the olive fruit fly are measured with yellow board fly catchers and phermone traps. When at least three flies are caught or when at least 5% of the fruit has been attacked by flies on the integrated olive tree plantations only the registered inseciticide may be used against them in the prescripted manner and therefore additional losses can be prevented. The regulations on organic olive tree cultivation allow the usage of only two prescripted insecticides which are to be applied when the above-mentioned pest reaches a certain state, if not the insecticides are without effect. In Italy and some other countries around the world they have tried to limit the olive fruit fly with a parasitic wasp but the effects in the natural habitat are very hard to estimate. Research in the coming years will enable even more opportunities and better quality olive tree cultivation in an organic way.
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