Strip‐management in rape crop: is winter rape endangered by negative impacts of sown weed strips?

Abstract

Abstract: With crop rotation as a fundamental element of the IPM and organic production, crop plants and their pests change beside permanent sown weed strips. Rape pests which are known to populate the fields from the edges might be augmented by sown weed strips. To evaluate whether weed strips have a negative impact on rape crop, insect pests and their antagonists were studied in a winter rape field near Berne, Switzerland, divided into two parts by a sown weed strip. They were registered at different distances from the weed strip and from the opposite field boundary in 1993. The pollen beetle Meligethes sp. and the cabbage weevils Ceutorhynchus assimilis Payk., C. napi Gyll. and C. pallidactylus Marsh and the brassica pod midge Dasineura brassicae Winn. were significantly more frequent near the field boundary than in the middle of the field and close to the sown weed strip. This could be because a sown weed strip does not act as a real field edge. For the investigated rape pods, 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 field 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 rate 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 efficiently increased the weed strip. Generally, no negative impact of the weed strip on rape crop was found and therefore sown weed strips could be suitable areas in a farming with crop rotation to diversity an agroecosystem.