Long-term experiments with reduced tillage in spring cereals. II. Effects on pests and beneficial insects

In four field experiments run for 7 years (1994-2000), the infestation of pests and the activity of carabids and staphylinids were compared in autumn ploughed and reduced tillage (no-tillage or spring harrowing) plots. Andersen (Crop Prot. 18 (1999) 651) reported the results from the first 4 years, while this paper deals with the results from the last 3 years. Herbicide treatments were added in the last 3 years, leading to fewer differences in pests and beneficial insects between the two treatments. This indicates that the effect of the weed cover, a secondary effect of the tillage regime, was more important than the direct effect of the tillage itself. The agromyzid Chromatomyia fuscula and the bird-cherry oat aphid, Rhopalosiphum padi were more numerous in autumn ploughed plots, probably due to healthier plants. Generally, more carabids were captured in reduced tillage, but no such difference was found for staphylinids. Several carabid and staphylinid species were correlated with different weed groups, while no species was correlated with percentage open soil. Different results for some closely related species emphasise the importance of analysing the effects on the species level. The importance of the details in the treatments chosen when comparing reduced tillage and conventional autumn ploughing are discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.