Intra- and interspecies competition of blackgrass and wheat in the context of herbicidal resistance and environmental conditions in Poland.

Blackgrass (Alopecurus myosuroides Huds.), one of the most aggressive grass weeds in Europe, is also a strong competitor of crops. This study aimed to assess the impact of environmental conditions on the competition between (1) ACC-ase and ALS herbicide-resistant (BR) and herbicide-susceptible (BS) blackgrass biotypes, (2) BR and winter wheat cv. Arkadia (W), and (3) BS and W. In the replacement series model, the experiment was conducted at seven sites across Poland during two seasons (2018/19 and 2019/20). In the BR-BS experiment, the BS biotype was in majority more competitive toward the BR biotype. However, in the regime of optimal hydrothermal conditions and at a higher sand content in the soil we observed a higher competitiveness of BR towards BS. The combined interactions between W and BR or BS were also affected by environmental conditions, i.e., soil texture and hydrothermal coefficient, as explained by PCA and k-means cluster analysis. At most sites, W was more competitive toward both BS and BR, which could result from earlier emergence of W in relation to B in majority of sites. Except for two cases, located on heavy, clay soils, during humid seasons, where B was more competitive toward W. We summarize that blackgrass competitiveness towards other biotypes and wheat depends to some extent on environmental conditions; however, the phenomenon should be explored in more detail.