Wheat is one of the most economically important field crops worldwide. Foliar diseases are a major threat to wheat productivity and are primarily managed by implementing less susceptible cultivars and using fungicides. With the “Farm to Fork” strategy under consideration by the European Union to reduce pesticide usage by 50% by 2030, this elucidates the importance of utilizing decision support systems (DSS) to optimize fungicide applications. Therefore, three DSSs of different origins, namely the IPM-Wheat Model Schleswig-Holstein (scientific), the ISIP system (federal), and the xarvio^© FIELD MANAGER (commercial), were analysed under maritime climate conditions at three locations in a high input area of wheat cultivation in northern Germany from 2019 to 2021. Fungicide efficacy was evaluated for yield as well as for the management of prevalent pathogens (Septoria tritici blotch, glume blotch, tan spot, powdery mildew, stripe rust, and leaf rust) on two different commercially available cultivars (highly and moderately susceptible). Compared to a stage-oriented standard system, no significant decrease in yield was observed in both cultivars, despite up to a 50% reduction in fungicide use through the use of DSSs. This was attributed to an optimized timing of fungicide applications, which resulted in slightly lower but still tolerable disease suppression efficacy compared to the stage-oriented system. In conclusion, minor disease severities are often overestimated, and DSSs can help improve the sustainability of fungicide use in wheat and pesticides in general.

Septoria tritici blotch (STB), caused by the fungus Zymoseptoria tritici Desm., is the most important disease affecting wheat in Northern Europe. There is a strong correlation between STB and weather variables; therefore, research on climate change and epidemiology is essential. In a long-term survey across 25 years, we evaluated the epidemiological development of STB at a representative location under maritime climatic conditions. The surveys conducted between 1996 and 2021 showed an increase in disease severity of STB with respect to time. At the survey location, the plants were also evaluated for other diseases, but other foliar diseases were only observed with negligible severities. However, a continuous increase in the severity of STB was observed throughout the survey. During the survey period, there was no significant relationship between disease severity and single weather parameters (e.g., temperature and precipitation). However, seasonal changes in the progression of conducive STB conditions within the season were observed during the survey. Therefore, STB infections occurred at increased temperatures due to infections later during the growth season. In general, the distribution of conducive weather conditions, which supports an infection, determines the epidemiological behaviour of STB during the growing season. Due to these enhanced STB epidemics, a decline in wheat production has been observed, especially in agronomic practices of maritime climates. This is particularly the case if temperature and precipitation during the growing season are affected by climate change.

Foliar diseases are a major threat to worldwide wheat production, especially during the vegetative period in maritime climates. Despite advancements in agronomic practices, infestations by foliar diseases are possible under favourable weather conditions, thus, fungicides are essential for maintaining control. Stage-oriented applications are therefore common in farm practices. The optimization of fungicide use according to biological–epidemiological thresholds reduces the total amount of fungicides used, which is of political interest, especially in the European Union. Therefore, the efficiency and effectivity of the fungicides used to control the six major foliar diseases (Septoria tritici blotch, glume blotch, tans spot, powdery mildew, stripe rust, and leaf rust) were analysed in a long-term study of 26 years in northern Germany under favourable maritime conditions. Of those diseases, Septoria tritici blotch was the most dominant recurring disease, with high severity noted in every year of the study. The threshold-based disease management system was compared to a fungicide untreated control and a healthy-standard fungicide treatment (according to growth stages). The usage of the threshold-based system reduced the disease severities significantly compared to the fungicide untreated control, without any loss of yield compared to the healthy-standard fungicide treatment. Thereby, the use of fungicides was reduced by two thirds compared to the stage-oriented healthy-standard treatment. Thus, the advantages of the threshold-based system were obvious, and this approach will be an important tool for future evaluations of current farm practices.