A Bolting-Resistant Strain of Detroit Beet |
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| Authors: | A A Jackson |
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| Institution: | Department of Horticulture, Wye College |
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| 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 four fungicide treatments, and the tentative conclusion was drawn that in this experiment these insects were less likely than the predacious mites to be a cause of the markedly different M. ulmi populations. However, as the plots were small and the trees very close, any differences in insect numbers caused by the treatments would soon be adjusted. A second large-scale trial was made at a more suitable site at Mellow Purgess Farm, Stondon Massey, near Brentwood, Essex in 1952–6, where plots were much larger, allowing several guard rows, and the trees were much younger and smaller, facilitating thorough spraying and representative sampling. Also, this relatively isolated orchard had received very few spray applications in the past and had never suffered from mite infestations at an economic level; Typhlodromus mites and several insect predator species were already present. |
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