Cultivation techniques as means to control pests in organic oilseed rape production

A field trial was conducted to compare the effectiveness of different husbandry practices in controlling pests in organic winter oilseed rape production. In oilseed rape, considerable damage and harvest losses can be caused by the cabbage stem flea beetle (Psylliodes chrysocephala), the pollen beetle (Meligethes spp.), the cabbage stem weevil (Ceutorhynchus pallidactylus), the oilseed rape stem weevil (C. napi), the cabbage seed weevil (C. obstrictus syn. assimilis) and the Brassica pod midge (Dasineura brassicae). A farming system that integrates means to promote natural enemies (mulching, a seed rate of 3.5 kg/ha, field margin weed strips, trap crop strips, drilling in a wide row (50 cm) and use of a hoeing machine for weed control in autumn and spring = mulching/hoeing treatment) was compared to a standard system (ploughing, conventional drilling technique, comb harrowing in autumn and spring, a seed rate of 5.0 kg/ha, no weed-strips or trap crop strips = ploughing/comb harrowing treatment). A third system, a mulching/comb harrowing treatment (mulching, a seed rate of 5.0 kg/ha, with weed- and trap crop strips) was also compared. The results were as follows: • An acceptable yield was achieved. In the ploughed treatment the yield was 2.65 t/ha; 20% higher than in the mulching treatments. • Trap crop strips (cv. Express) which were sown in the treatments with mulching showed (compared to field edges without trap crop strips) a higher infestation by the Brassica pod midge, the cabbage seed weevil and the pollen beetle than the crop plants within the field (cv. Oase). For the cabbage stem weevil however no significant differences were recorded. • While the Brassica pod midge achieved the highest reproduction rate within the mulching/hoeing treatment, for all other pests the highest reproduction rate was recorded in the ploughing/comb harrowing treatment. • The highest abundance of predators active on the soil surface was recorded in the mulching/comb harrowing treatment. Due to the higher abundance of natural enemies, the reproduction rate of all pest species (except the pollen beetle) was lowest in the mulching/comb harrowing treatment. Thus, in this treatment considerably more larvae had to be invested to produce one mature individual of the new pest generation. All treatments showed advantages and disadvantages: the ploughing/comb harrowing treatment achieved the highest yield, but also the highest hatching rates of pests of the new generation (except the Brassica pod midge). The mulching/comb harrowing treatment promoted natural enemies, but there is a higher risk of yield losses due to weeds. In the mulching/hoeing treatment, the reduction of the weed risk by mechanical means was followed by a reduction in numbers of natural enemies. Furthermore, in this treatment a higher infestation by the Brassicae pod midge and other occasional pests occuring in autumn (e.g. Athalia rosae, Plutella xylostella, Myzus persicae) was recorded. This one-year field trial clearly demonstrated that organic oilseed rape cultivation is potentially possible if relevant husbandry practices are considered and used in an appropriate way.