Effects of Environmental and Agronomic Factors on the Dispersal of Multiple Resistant Lolium rigidum in Malt Barley Fields of Northern Greece

In this study, a survey was conducted in 14 fields (6 in Thessaloniki and 8 in Serres) before barley harvest during three growing seasons (2019–20, 2020–21, 2021–22) to map the occurrence of ACCase and ALS multi-resistant populations and evaluate the influence of agronomic practices and environmental conditions on their dynamics. Specifically, weed cover and tiller number/plant were assessed in each field using a W pattern, while questionnaires were used to collect information from farmers on agronomic practices applied, such as seedbed preparation, the rate of fertilization at sowing, the time of sowing, the time and rate of top-dressing nitrogen fertilizer, the time of application of the herbicide pinoxaden, and the harvest time. Soil properties and climatic conditions were also recorded. These results indicated that regardless of the different agricultural practices applied in the fields of the studied regions, no significant association was found with L. rigidum’s ground cover or number of tillers/plant. Additionally, no association was identified between weed ground cover and climatic characteristics. Therefore, the findings of this study strongly support the dependence of the dispersal of the resistant strain L. rigidum on the interactions between genetic, biological, and soil factors; fertilizer or herbicide use; sowing or other agronomic practices; and climatic factors that drive resistance dynamics, rather than any individual practice alone.