Damages on sugar beets by the pygmy mangold beetle (Atomaria linearis) - danger thresholds -

Longtime observations (since 1955) on the occurrence of the pygmy mangold beetle (Atomaria linearis Steph.) show it still being an important early pest with sugar and fodder beets. Nevertheless, the since 1974 developed, now on the market available seed pellets containing carbofuran (30 g a.i./100,000 pellets) can avoid damages in case of light and medium infestation. Damage threshold of untreated seeds: seeds not treated with insecticide are endangered when at time of emergence an average of more than 2.3 beetles per 100 ml of root ball occur. Emergence rate and degree of infestation (D.o.I.) are in this case approximately the same with pellets containing carbofuran (CP) or not. Already in case of an average of 3.5 beetles/100 ml root ball the emergence rate of untreated pellets as against CP is reduced by 19.2 per cent and the D.o.I. goes down to 0.62 with non-treated ones. In case of an average of 7.1 beetles the emergence rate goes down to 35.2 per cent, the D.o.I. increasing to 0.53 - i.e. each hypocotyl showing an average of two bites. Pot trials with untreated seeds have confirmed these results: here the damage threshold was 2 beetle/pot (giving 5 plants/pot). When over 5 beetles/top the number of plants/pot diminished to an extent similar to the field trials. Damage threshold of CP: trials with current CP have shown that with an average of up to 13.6 beetles/100 ml root ball an even emergence still occurs with a D.o.I. of only 0.86 - i.e. each plant has suffered an average of less than a bite. Only with 20 and more beetles a clear emergence diminution of abt. 10 per cent and an increasing of the D.o.I. to 0.54 can be observed - i.e. an average of two bites/plant. By additional application of insecticide granules (e.g. curaterr with 0.4-0.5 g/meter of seed row) the emergence rate cannot be increased but the seed conditions of the young plants are improved. This can be as well achieved through additional spraying right after emergence