Biocontrol of apple aphids apple orchards E10
Research Institute of Organic Agriculture, Bernhardsberg, CH-4104 Oberwil, Switzerland
|To attract antagonists of apple aphids in an
organic apple orchard in Switzerland we have integrated weed strips consisting of 20
endemic flower species. In the year before the experiment, in 1991, the apple aphids and
the predators of aphids were homogenously distributed in the orchard. In April 1992, weed
strips were sown between the tree rows and along the border of one part of the orchard;
the other part served as control.
In both parts of the orchard, randomly chosen trees were controlled visually and by beating tray samples in weekly intervals in 1991 to 1994. During the flowering time of the weeds significantly more predators of aphids were found on 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 on apple trees at that time. There were significantly more spiders and spider webs recorded on trees in the strip-managed part than on 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 leaded to a three to five times lower number of apple aphids in the strip-managed part than in the control part of the orchard.
The weed strip-management in apple orchards was an adequate measure in two years of low to normal abundance of aphids. However, in one year of high abundance, aphid population exceded the economical threshold.
Wyss, E. (1995): The effects of weed strips on aphids and aphidophagous predators in an apple orchard. Entomologia Experimentalis et Applicata, 75, 43-49.
Wyss, E.; Niggli, U. & Nentwig, W. (1995): The impact of spiders on aphid populations in a strip-managed apple orchard. Journal of Applied Entomology, 119, 473-478.