The paper presents the results of three-year investigations (1999-2001) upon the effect of different method of plant protection on the yielding of spring rape, ‘Star’ (conventional) and ‘Margo’ (F₁ hybrid). Throughout the research period the highest yield was recorded following the application of full chemical control (Butisan 400 SC + Decis 2.5 EC + Ronilan 500 SC). Classifying the biotic agents from the most to the least grain-yield decreasing, the following order was noted: insects – weeds – diseases, which was due to a high reduction of generative organs, mainly by pollen beetle (Meligethes aeneus F.), seen as a lower number of siliques on the main stem and the number of seeds per silique. Multiple regression analysis showed that the yield of seeds was determined mainly by the number of siliques on the main stem and on lateral branches.

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