Potential of herbicide reduction by automatic spot spraying in sugar beet with regard to weed control and biodiversity

Reducing pesticide use while maintaining crop productivity is one of the biggest challenges in modern agriculture. Spot spraying systems can achieve significant herbicide savings in weed control. This is true in particular for less competitive crops and with high herbicide treatment indices. In order to test the savings potential under practical conditions in the field, the effectiveness of a spot spraying system (WeedSeeker 2, FarmFacts Germany) was evaluated in a one-year pilot project. The study included two intensity levels in comparison with standard site practice and an untreated control in a sugar beet experimental field with each four replicates. Therefore, the degree of weed coverage, the weed density and the number of weed species present were recorded before and after each of the three treatments by visual assessment. After the last application, the abundance and diversity of soil arthropods was additionally recorded. Finally, the herbicide savings potential at a given weed density, the control success and differences in abundance and diversity of the recorded species between the treatments were compared. Our results show that a considerable decrease in herbicide use is possible with the given technology, however, weed densities remained above the economic threshold for the most dominant weed, Chenopodium album L. Additionally, there was a trend of a higher abundance of soil arthropods, including carbides, in the untreated plots in comparison to the different herbicide treatments. However, the biodiversity indicated by the Shannon index was not reduced. Overall, the spot spraying treatment did not lead to an improvement of biodiversity parameters in comparison to the broadcast standard spraying method. Therefore, a continuous improvement of the application technique is required to ensure stable yields while at the same time reducing pesticide use.