STRIP-MANAGEMENT IN RAPE CROP - IS WINTER RAPE ENDANGERED BY NEGATIVEIMPACTS OF SOWN WEED STRIPS

With crop rotation as a fundamental element of the LPM and organic pro duction, crop plants and their pests change beside permanent sown weed strips. Rape pests which are known to populate the fields from the ed ges might be augmented by sown weed strips. To evaluate whether weed s trips have a negative impact on rape crop, insect pests and their anta gonists were studied in a winter rape held near Berne, Switzerland, di vided into two parts by a sown weed strip. They were registered at dif ferent distances from the weed strip and from the opposite field bound ary in 1993. The pollen beetle Meligethes sp. and the cabbage weevils Ceutorhynchus assimilis Payk., C. napi Gyll. and C. pallidactylus Mars h. and the brassica pod midge Dasineura brassicae Winn. were significa ntly more frequent near the held boundary than in the middle of the fi eld and close to the sown weed strip. This could be because a sown wee d strip does not act as a real field edge. For the investigated rape p ods, little difference was observed as to the rate of infestation of C . assimilis. It was astonishing that only a few predators were caught by sweep netting in the whole held as well as close to the weed strip. A higher number of parasitoids near the sown weed strip could not be found either, which was probably due to their high mobility. The low r ate of parasitization of the rape pests was only once assessed clearly higher near the weed strip than in the rest of the field. Therefore, flower visiting predators and parasitoids might not have been efficien tly increased the weed strip. Generally, no negative impact of the wee d strip on rape crop was found and therefore sown weed strips could be suitable areas in a farming with crop rotation to diversity an agroec osystem.