A four year study investigated some soil-inhabiting pests which cause damage to sugar-beet seedlings. Sampling methods are discussed and a convenient and quick flotation technique for extracting arthropods from soil samples, and other methods, are described. Soil sampling sugar-beet fields in Spring, at many pest-infested sites, showed that blaniulid millipedes, pygmy beetle (Atomaria linearis) and onychiurid Collembola migrate from the subsoil and inter-row spaces and move progressively into the rows where they aggregate around sugar-beet seedling roots. 'Drilling-to-a-stand', with the concomitant wider seed spacing, sometimes increased numbers of millipedes and pygmy beetle per seedling root-zone, but never, onychiurid Collembola. Seedling roots at 9 in. spacing were usually damaged more than those from seed spaced at either 1 in. or 1.5 in. but the narrowest spacing sometimes improved seedling growth. Seedlings were smaller on plots receiving a pre-emergence herbicide but numbers of root-zone pests and damage was not affected. The damage to seedlings caused by millipedes is described in detail; it was also confirmed that Onychiurus spp. Collembola could kill seedlings in the laboratory and were generally the most common soil-inhabiting pest. Some factors which may affect damage by soil-inhabiting pests in the field and laboratory were reported. Timing of sowing could affect seedling survival; raw and pelleted seed was differentially attractive to some pests; soil compaction was sometimes beneficial. The biology and life-history of millipedes (Brachydesmus superus) and two common blaniulids: Blaniulus guttulatus and Boreoiulus tenuis was studied both in the field and in the laboratory. Two autumn surveys plotted the distribution of millipedes in the major sugar-beet growing areas in England. Some aspects of millipede behaviour were studied in the laboratory; soil temperature levels affected both their orientation and pattern of feeding behaviour; vertical and horizontal soil columns tested their reaction to soil moisture status. Studies on the effect of different insecticides showed that seed-treatments may be effective in the laboratory but their performance in the field, against millipedes, was inconsistent. Many insecticides, in seed or furrow formulation, killed pygmy beetle; the currently recommended insecticide, gamma-BHC, performed consistently well but was toxic to a mite predator of Onychiurus.
|Date of Award||1975|