LABORATORY EVALUATION OF THE SIDE-EFFECTS OF PESTICIDE MIXTURES USED IN APPLE ORCHARDS ON THE PREDATORY MITE TYPHLODROMUS-PYRI SCHEUTEN

In laboratory studies, the initial and acute toxicity of different mix tures of pesticides and their effect on the reproduction rare of the p redatory mire Thyphlodromus pyri Scheuten were compared to sole applic ations of one kind of pesticides using standardized glass-plate-rests. Mortality after 1 and 6 days and reduction of the reproduction rare w ere registered. The pesticide mixtures were derived from commonly used combinations in apple orchards. The effects of the pesticide combinat ions were investigated by comparing the observed and expected effectiv e mortalities. The expected effective mortality was based on the sum o f the mortalities of the two pesticides. A synergistic effect was assu med when the observed effective mortality was significantly greater th an the expected effective mortality. An increase of mortality caused b y the summation of the toxicity of each pesticide was observed using t he combinations Dithane Ultra + Benocap and Delan + Pirimor. A synergi stic effect could be detected using the combination of Systane 6W + Po lyram WG, Omnex plus + Rubirox and Systane 6W + Rubitox. Although Kara thane used solely or as a mixture with Polyram Combi showed the same a cute toxicity after 6 days, an increase of 44 % above the expected ini tial toxicity could be observed only 1 day after application. Other pe sticide mixtures showed no significant increase of effective mortality of the mites when mixtures were compared to each pesticide. The repro duction ion rate of the predatory mires was significantly decreased wh en the mixtures Polyram Combi + Karathane, Omnex plus + Rubitox, Systa ne 6W + Rubitox and Insegar + Pirimor are compared to each pesticide u sed solely.