Prevention of vole damage in organic pomiculture

Summary

Vole damage is one of the most difficult phytosanitary problems to solve in organic
pomiculture. A survey conducted in 2002 among German fruit growers showed that 90
% of the farms suffered from this damage. The water vole (A. terrestris) revealed to be
the main pest in 80 % of the orchards. 61 % of the farmers announced a high interest in
the development of new preventive and control methods. To stop immigration of voles
into orchards a mechanical barrier system was developed and tested at two study sites
in Baden-Wuerttemberg and Rhineland-Palatinate. At each location barrier systems with
wire mesh (mesh size 10 mm) and polyolefine-foil were installed arround two 0.7 ha
study plots. Two unprotected plots were used as a control. The barriers were anchored
20 cm deep into the soil. 30 cm of the material protruded over the surface. Automatic
gates were installed for the entrance of vehicles. 4 persons needed approximately one
day to install a barrier around a plot with the size of 1 ha. Not only was the wire mesh
cheaper than the foil, it was permeable for wind, water and small beneficial organisms.
After installing the barrier systems, voles were removed from all plots. Snap trap boxes
were ranged along the outside of the barriers to catch migrating voles. A total of 33
water voles and 1263 common voles (M. arvalis) were captured on both study sites from
October 2002 to November 2003. During the study period a total of 5 water voles
immigrated into the first control plot and 6 settled into the other plot. Four water voles
entered two of the barrier protected plots by using fresh mole galleries. The other
protected plots stayed free from water voles. Simultaneous to the field studies, trials in
two enclosures were carried out in Muenster. The barriers kept all water voles outside
the protected plots. The results showed a high efficacy of the developed barrier system.