A long-term study of crop rotations, herbicide strategies and tillage practices: Effects on Alopecurus myosuroides Huds. Abundance and contribution margins of the cropping systems

Abstract

Alopecurus myosuroides Huds. (blackgrass) frequently occurs in Western European cropping systems. It causes high yield losses in winter-cereals and winter-oil-seed rape. Several preventive measures to control blackgrass are available, however long-term studies with combinations of preventive and direct control methods are rare. In this seven-year study at two locations in Germany, three crop rotations with different proportions of winter-annual crops, four herbicide strategies and four tillage measures were combined and their interactions were analyzed. Aim was to investigate the effects on blackgrass densities, crop yields and contribution margins. Densities increased from 14 to 3098 heads m-2 and 201 to 3563 heads m-2 in the rotation containing only winter-annual crops without weed control and reduced tillage. Rotations with spring crops reduced densities by up to 98%. Inversion tillage with a moldboard plough and false seedbed preparation using a harrow (shallow) and a rotary harrow (deep) reduced blackgrass infestations by up to 70% compared to solely reduced conservation tillage with a chisel plough. Blackgrass densities were 23–99% (average 59%) lower, when herbicide Mode of Action (MOA) was rotated in every year compared to herbicide strategy continuously using the same MOA. Grain yield loss in the control plots due to blackgrass competition amounted up to 3.0 t ha-1 (41%). Contribution margins were highest in the cropping systems that combine crop rotation, inversion tillage, false seedbed preparation and herbicide MOA rotation. The results highlight the benefits of integrated weed management in regard to weed control and economic sustainability.