Effects of climate change on the dispersion of white grub damages in the Austrian grassland

Summary

Recent changes in occurrence of agricultural pests in Austria might already reflect climate change phenomena. In this study, an inventory of white grub (Melolontha melolontha, Amphimallon solstitiale and Phyllopertha horticola) damages in Austrian grassland including organic cultivation was performed by questioning plant protection consultants of 74 Agricultural County Chambers. Altogether, a cumulated 14.800 hectares of white grub damages were recorded. From 2000 onwards, a steady increase of white grub damages occurred with a climax in the year of heat and drought 2003. The infested fields extended along the alpine main ridge from Vorarlberg up to the alpine foreland. Additionally, southern slopes of the Danube valley in Upper and Lower Austria were affected. Very likely, the damages were mainly due to the garden chafer P. horticola. From 2004 to 2006, the extent of damages decreased again all over Austria. By studying meteorological data, it became obvious that the damaged areas were mainly situated in regions with a strong precipitation deficit. On-farm investigations performed in 2007 strengthened the hypothesis that drought and elevated soil temperatures might be the decisive factors for a strong development of grub populations and subsequent feeding damages. Additionally, drought can increase the effects of grub damage by delaying the regeneration of the damaged sward. A strongly damaged sward on slopes can be dangerous for the farmers e.g. by slipping machines.