Die Wirksamkeit von Einflugbarrieren gegen die Besiedelung von Broccoli und Kohlrabi durch die Kohldrehherzgallmücke Contarinia nasturtii (Diptera: Cecidomyiidae).

Summary

Abstract: The effect of exclusion fences on the colonization of broccoli and kohlrabi by the Swede midge, Contarinia nasturtii (Diptera: Cecidomyiidae).
The Swede midge Contarinia nasturtii (Diptera: Cecidomyiidae) is an important and wide spread pest in Europe. In Swiss organic vegetable production only the expensive product “Audienz“ (active matter: Spinosad) is permitted. In addition, netting the entire crop surface can exclude the Swede midges from crops, but it has a negative influence on the microclimatic conditions and the labour and capital cost are often too high. Since it is known, that several vegetable key pest species spread within the crop or only a few centimetres above it, the use of vertical exclusion fences has been developed in Canada. The objective of our study was to exclude C. nasturtii from the crops by using a similar, but cheaper prototype of exclusion fence.
The studies were undertaken on two fields (broccoli and kohlrabi) and the effect of the fences (fenced in area: 15x20m for broccoli, 7.5x20m for kohlrabi; height of fences: 1.4m with a 0.25m overhang; 4 replications each field) was compared with an untreated control and with a treatment of „Audienz“ (3 applications, 0.5l/ha). At harvest the damages were assessed by classifying the symptoms of 100 plants per treatment and replication in three (kohlrabi) or four (broccoli) categories. Inside the fences 100 plants near the fence and 100 plants in the centre were visually controlled.
The exclusion fences significantly reduced the damages caused by the Swede midge. The treatment of “Audienz“ reduced the damages, too, but in the broccoli trial, “Audienz“ had a significantly lower effect than the fences. The effectiveness of “Audienz” with 36.4% (broccoli) and 58.3% (kohlrabi), respectively, was lower than the effectiveness of the fences: 69.1% and 60.0% near the fence and 77.8% and 78.9% in the centre. The results are discussed.