Suppressing Alopecurus myosuroides Huds. in Rotations of Winter-Annual and Spring Crops

Abstract

Alopecurus myosuroides Huds. has become one of the most abundant grass weeds in Europe. High percentages of winter-annual crops in the rotation, earlier sowing of winter wheat and non-inversion tillage favor A.myosuroides. Additionally, many populations in Europe have developed resistance to acetyl-CoA carboxylase (ACCase), acetolactate synthase (ALS) and photosynthetic (PSII) inhibitors. Hence, yield losses due to A.myosuroides have increased. On-farm studies have been carried out in Southern Germany over five years to investigate abundance, control efficacies and crop yield losses due to A.myosuroides. Three crop rotations were established with varying proportions of winter- and summer-annual crops. The crop rotations had a share of 0, 25 and 50% of summer-annual crops. Within each crop rotation, three herbicide strategies were tested. In contrast to classical herbicidal mixtures and sequences, the aim of one of the herbicide strategies was to keep selection pressure as low as possible by using each mode of action (MOA) only once during the five years. A.myosuroides population was susceptible to all herbicide at the beginning of the experiment. Initial average density was 14 plants m−2. In the rotation with only winter-annual crops, density increased to 5347 ears m−2 in the untreated control plots. Densities were lower in the rotations with 25% and even lower with 50% summer-annual crops. Control efficacies against A. myosuroides in the herbicide strategy using only MOAs of the HRAC-groups B and A, according to the Herbicide Resistance Action Committee (HRAC) classification on MOA, dropped after five years compared to the strategy of changing MOA in every year. Nevertheless, the results demonstrate the need for combining preventive and direct weed-management strategies to suppress A.myosuroides and maintain high weed-control efficacies of the herbicides.