Enhancement and release of predaceous arthropods to control aphids in organic apple orchards | [Amélioration et relargage d'arthropodes prédateurs pour lutter contre les pucerons dans les vergers biologiques de pommiers]
1999
Wyss, E. ((Research Institute of Organic Agriculture, Frick (Suisse)))
As an indirect strategy to control apple aphids, weed strips consisting of 20 endemic flower species were integrated in an organic apple orchard to attract antagonists of apple aphids. During the flowering time of the weeds significantly more predators of aphids were found in the trees of the strip-managed part of the orchard than in the control. With the decrease of flowering in the weed strips in autumn the number of predators of aphids on the trees dropped, as well. However, several polyphagous spider species were frequent in apple trees at that time. There were significantly more spiders and spider webs recorded in trees in the strip-managed part than in trees in the control. Therefore, more aphids were caught in spider webs in autumn when aphids were returning from their sommer host plants to the apple trees. The higher number of aphidophagous and polyphagous predators during the critical periods led to a three to five times lower number of apple aphids in the strip-managed part than in the control part of the orchard. In addition to the enhancement some predators of aphids were tested for inundative releases during the period of hatching of the fundatrices in spring. Results of studies in fieldcages showed that released larvae of Adalia bipunctata L. and Episyrphus balteatus L. significantly reduced the number of aphids. In 1997, first studies of controlled release in orchards showed similar results for A. bipunctata in high predator-prey-ratios (5:1 and 1:1) independent of the presence of ants
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