The side effects of lime sulphur on predaceous arthropods, i.e. Typhlodromus pyri, and other leaf occupying arthropods

Abstract

Conclusions and further studies The significant reduction of T. pyri and of larvae of predaceous gall midges, the complete loss of mite-diversity and the possible enhancement of P. ulmi and other harmful mites (i.e. C. vitis) are clear disadvantages of lime sulphur. Densities of T. pyri between 0.5 and 1 mite per leaf as mentioned to be necessary for controlling harmful mites (BOURQUIN 1989, FORTMANN 1993, HARZER 1993, KARG 1992, KOHLER ET AL. 1991), were never reached in lime sulphur treatment, while the untreated control always showed densities above this value. On the other hand low densities of predaceous mites are quite normal in intensively sulphur treated, biological orchards and are often replaced by other mite predators, like predatory bugs (Miriadae, Anthocoridae) or the coccinellid beetle Stethorus punctillum (HÄSELI & BOSSHARD 1994). Therefore further studies should include these arthropods, because lime sulphur may also have adverse effects on them (BORIANI 1994, BROWN 1978). Furthermore the lowest application strategy in terms of frequency and concentrations for scab control should be examined to minimise the quantity of applied lime sulphur (ZIMMER 2000). In addition the effects of different application methods, for example by sprayer or overhead irrigation on beneficial arthropod as well as on scab should be studied (KELDERER ET AL. 2000). The side effects of lime sulphur should not be considered separated from other used fungicides, moreover the whole spraying program should be included, because wettable sulphur (MILAIRE ET AL. 1974) and clay powder (HÄSELI & BOSSHARD 1994) also harm arthropods. For agronomic interests but also from the points of view of the registration of lime sulphur and the public image of organic apple growing, the question is: whether lots of preventive applications with copper, sulphur and clay powder have more adverse effects on beneficial arthropods than fewer curative applications of lime sulphur by using an infestion prediction model. Only by further studies under realistic farming conditions it is estimable, whether the use of lime sulphur in organic orchards can be accepted. In the common enthusiasm about this new curative fungicide, we should not forget the important role of beneficial arthropods. In this context the registration without any indication in the EU should be critically discussed