Cornflower (Centaurea cyanus L.), one of the main weeds found among winter crops in Poland, has developed herbicide resistance (HR) to acetolactate synthase (ALS) herbicides, a finding first reported in 2006, and in recent years, farmers have been complaining about inadequate chemical control of this weed. This study aimed to characterise the current state of cornflower HR to ALS inhibitors and synthetic auxins in Poland and the agricultural practices in fields with herbicide-resistant populations. From 2017 to 2020, 159 seed samples together with the field history were collected across the country and biological tests performed in glasshouses. This revealed that 47 populations of C. cyanus were cross-resistant to both tribenuron and florasulam, 28 and 8 populations were single resistant to tribenuron and florasulam, respectively, and 3 populations had developed multiple resistance to both ALS inhibitors and synthetic auxins, i.e., 2,4-D and dicamba. Resistant populations were found mostly frequent in northern Poland, but also in the eastern and western parts of the country. Based on a survey of farmers, the resistant populations were found in winter crops regardless of the tillage system (77% of fields with HR cornflower were mouldboard ploughed). Based on the proposed population treatment (PT) index showing the frequency of herbicide use during three consecutive seasons on farms with HR cornflower, the average PT for all the surveyed farms was 5.4. The highest PT of 7.4 was found in the province of Warmia-Masuria in northern Poland.

Competitive ability of cereals against segetal weeds depends among other things, on soil properties and the weather. Concerning cornflower (Centaurea cyanus L.), this issue is poorly recognized, as there are no reports on the impact of environmental conditions on the competitiveness of wheat against susceptible and resistant biotypes. Our study aimed to evaluate the effects of site and weather conditions on the competitive effects between winter wheat (WW) and two cornflower biotypes, either florasulam and tribenuron-methyl resistant (R) or sensitive (S). The experiment was conducted in a replacement series model at six sites across Poland in three growing seasons. The competitive relations were determined on the basis of two indices, i.e., the relative biomass and the number of seeds produced by the tested plants. The relative yield of wheat and weed were plotted on graphs and fitted to one of five competition models. In addition, a competitive ratio (CR) was calculated on the basis of fresh plant biomass and the number of seeds. Correlation coefficients were determined between the length of the plant, yield, biomass, the number of seeds per plant, hydrothermal coefficient K, and soil texture. Biometric parameters of wheat for its competition with two cornflower biotypes were analyzed using canonical variate analysis (CVA). The number of days to WW emergence and the day-difference between WW and cornflower (B) emergence were also calculated. The environmental characteristics of the sites, i.e., hydrothermal coefficient K and soil texture, were used as categorizing variables. Drought generally favored the greater competitive ability of WW against B for both biomass accumulation and seed production. During the first season of the research (relatively dry), only in one case out of 12 cases cornflower was more competitive than wheat. In the second year of the experiment (dry season), the competition of WW against B for resources was lower. It depended more on the site than on the cornflower biotype or the proportion of plants in the mixture. Under high or optimal rainfalls (the third year of the experiment), the competitiveness of WW toward B was significantly lower than in years with rainfall deficiency. In addition, the ability of wheat competition against the weed may have been influenced by the earlier emergence of wheat than cornflower. Even though it was sown together with wheat, cornflower emerged 0–12 days later than the tested cereal. It was also noticed that wheat was more competitive on light soils against the herbicide-susceptible (S) biotype. In contrast, greater WW competitiveness was observed against herbicide-resistant (R) cornflower on heavy soils. In conclusion, winter wheat competitiveness against herbicide-resistant or herbicide-sensitive cornflower biotypes is significantly dependent on weather and soil conditions. It is therefore reasonable to study this phenomenon in more detail. It would also be interesting to learn more about the underground competition on varying soil types under different water availability.

In experiments with weed harrowing crops are negatively affected by competing weeds but also by the destructive effect of used implement. This research was carried out to find growth stages during which mixture of oat (Avena sativa L.) and triticale (× Triticosecale Wittm.) was resistant to harrowing and was able to effectively recover from this physical disturbance. Plots were harrowed 1–3 times on the same day at six consecutive stages of mixture growth with spring-tine harrow. After the latest harrowing, all plots were sprayed with herbicide to exclude competitive effect of weeds on the mixture. Compared to non-harrowed plots plant density of mixture was significantly reduced after a single cultivation at 1- and 2-leaf stage (20% and 23% respectively), two cultivations at 3-leaf stage (22%) and three at the beginning of the tillering (21%). No yield penalty was noticed for the density reductions, thus showing high ability of mixture to recover from physical disturbance. We recommend plant emergence as an appropriate growth stage for single harrowing of oat-triticale mixture. Two cultivations on the same day should not be planned earlier than at the beginning of tillering.

The study evaluated the effect of intercropping Paulownia (Paulownia spp.) with spring barley (Hordeum vulgare L., cv. KWS Thalis) on selected components of agroecosystem biodiversity under Polish conditions. A field experiment established in 2019 compared an alley cropping system with barley monoculture during the 2025 growing season. Weed infestation, soil microbial communities, mesofauna abundance, and crop yield were assessed. Weed abundance was lower in the intercropping system than in monoculture, reaching 5.6 vs. 15.6 plants m⁻² at BBCH 21 and 21 and 22.8 vs. 35.6 plants m⁻² at BBCH 75. Bacterial alpha diversity was significantly higher under intercropping conditions, with Shannon index values ranging from 5.12 to 5.25, compared with 4.98–5.09 in monoculture. Fungal diversity showed moderate differences between systems, whereas the abundance of Collembola and Acari was influenced mainly by seasonal variation rather than by cultivation system. No significant reduction in barley yield was observed under intercropping conditions. The results suggest that Paulownia-based alley cropping may reduce weed pressure and support selected soil biological properties without negatively affecting crop productivity. However, the observed responses varied depending on the analyzed parameter and sampling period, indicating the preliminary and context-dependent character of the results. Further long-term studies are required to better understand the ecological mechanisms operating in such agroforestry systems.

Intercropping has emerged as a promising strategy to improve agroecosystem biodiversity and mitigate some adverse effects associated with intensive monoculture systems. This study evaluated weed infestation and biodiversity responses in a Paulownia –buckwheat intercropping system compared with buckwheat monoculture under the environmental conditions of southwestern Poland. Weed species composition, abundance, and biomass were assessed at different growth stages of buckwheat. Selected agroecosystem components, including soil microorganisms, soil mesofauna, and pollinator abundance, were evaluated. The intercropping system increased Collembola diversity and Acari abundance, while higher diversity and richness of segetal plant species were also observed compared with monoculture. Higher bacterial abundance and dehydrogenase activity were recorded under intercropping, whereas fungal community composition remained generally stable between cultivation systems. Several melliferous weed species were identified within the intercropping system, potentially supporting pollinator activity. Although no statistically significant differences were observed in pollinator-related parameters, nectar productivity and sugar availability tended to be higher under intercropping conditions, suggesting that the Paulownia –buckwheat system may contribute to maintaining pollinator activity and supporting agroecosystem biodiversity. No significant differences in buckwheat yield or biometric traits were found between cultivation systems. Overall, the results indicate that Paulownia –buckwheat intercropping may enhance selected components of agroecosystem biodiversity without reducing crop productivity.