Further Studies on the Influence of Fungicide Sprays on the Balance of Phytophagous and Predacious Mites on Apple in South-East England

Abstract

The importance of the fungicide used for Apple Scab control in affecting the development of harmful populations of the Fruit Tree Red Spider Mite, Metatetranychus ulmi (Koch), has been noted by Gilliatt (1935), Cutright (1944) and Pickett et al. (1946). The advent of the relatively specific organic fungicide glyodin (Chandler and Thurston, 1949) offered a hope of scab control with a minimum of side-effects on arthropod populations and hence of assessing the role of predators in the control of M. ulmi. In a preliminary trial in Kent (Collyer and Kirby, 1955), on plots sprayed with one or another of four fungicides in 1951–3, higher populations of M. ulmi developed following lime sulphur sprays than after glyodin or captan ; wettable sulphur gave an intermediate result. Conversely, higher populations of predacious mites (Typhlo- dromus spp.) were present on glyodin- or captan-treated trees than on trees receiving lime sulphur. No apparent differences in populations of predatory insects resulted from the fou...