Composition of the weed flora in sugar beet cultivation in Germany - nationwide trials 1995-2022

Long-term data from 449 herbicide trials across Germany from 1995-2022 were used to characterise the weed composition in sugar beet cultivation. The assessments of 1782 untreated control plots showed local weed species composition and weed pressure. The most common weeds were Chenopodium album (82.3% of all plots), Polygonum convolvulus (52.2%) and Galium aparine (25%). The average number of weed species in the field trials decreased from 4.9 in 1995 to 2.6 in 2022, significantly influenced by trial location and year. The occurrence of the most frequent weeds has also changed. C. album and P. convolvulus increased while G. aparine and Matricaria chamomilla decreased. Possible reasons for these changes are different tillage systems and intensities as well as changes in crop rotation with decreased crop diversity. Herbicide treatments and different active ingredients also affect the occurrence and proportion of weeds. The trial sites were assigned to clusters accounting for climate attributes and soil properties to identify regional differences in weed infestation. Regions with low soil quality, high temperatures and low precipitation had higher weed diversity, presumably due to low crop cover and, thus, lower weed suppression. The proportion of C. album was very high in all regions because it can grow under a wide range of environmental conditions. For P. convolvulus, significant regional differences existed in its proportion of total weed infestation. Its importance was lower in regions with poorer soils.