Comparison between the application of insecticides and the use of polyethylene-nets in controlling cabbage root fly Delia radicum on Chinese cabbage
1992
Merz, F. (Landesanstalt fuer Pflanzenschutz, Stuttgart (Germany))
The use of the polyethylene-nets Bionet K and Rantai K had proved effective against cabbage root fly (Delia radicum) in radish. From 1988 to 1990 the efficacy of the nets was further investigated in Chinese cabbage. Covering the plants with nets was compared with spraying the insecticides Lannate 25-WP (Methomyl, 230 g a.i./ha), Nexion stark (Bromophos, 230 g a.i./ha), E 605 forte (Parathion, 105 ga.i./ha) or Ecombi (Oxydemeton-methyl, 120 g a.i./ha + Parathion, 105 a.i./ha). The cabbage root fly larvae damaged 20 - 100 per cent of the untreated field-sown or planted Chinese cabbage. Bionet K and Rantai K protected the plants almost completely from the root fly damage. In one field trial the nets were also effective against caterpillars. But on three fields there was severe damage caused by Mamestra brassicae and Noctua pronuba. Larvae of the cabbage butterfly (Pieris rapae) were only found in the untreated plots. However, in these trials the Chinese cabbage plants were covered one or two weeks after planting. It is concluded that the caterpillars emerged from eggs laid in this period. Further tests will be necessary to investigate the possibility of oviposition through the nets and the role of butterflies emerging from puparia in the soil. The foliar sprayings of insecticides were less effective against the root flies. The effectiveness against caterpillars was high in fields where the crops had been sprayed two times. One treatment was ineffective. Net covers on Chinese cabbage plants had only negligible effect on Alternaria spp. infection. Compared to the insecticide application the nets proved economic
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