Corn poppy (Papaver rhoeas L.) and cornflower (Centaurea cyanus L.) are two overwintering weed species found in crop fields in Europe. They are characterised by a similar life cycle, similar competitive efforts, and a spectrum of herbicides recommended for their control. This review summarises the biology and herbicide resistance phenomena of corn poppy and cornflower in Europe. Corn poppy is one of the most dangerous dicotyledonous weeds, having developed herbicide resistance to acetolactate synthase inhibitors and growth regulators, especially in Mediterranean countries and Great Britain. Target site resistance to acetolactate synthase inhibitors dominates among herbicide-resistant poppy biotypes. The importance of non-target site resistance to acetolactate synthase inhibitors in this species may be underestimated because non-target site resistance is very often associated with target site resistance. Cornflower, meanwhile, is increasingly rare in European agricultural landscapes, with acetolactate synthase inhibitors-resistant biotypes only listed in Poland. However, the mechanisms of cornflower herbicide resistance are not well recognised. Currently, herbicides mainly from acetolactate synthase and photosystem II inhibitors as well as from synthetic auxins groups are recommended for the control of both weeds. Integrated methods of management of both weeds, especially herbicide-resistant biotypes, continue to be underrepresented.

The spread of invasive plants is one of the most significant causes of biodiversity loss in natural, semi-natural, and anthropogenic habitats in Poland. This two-year study aimed to assess the rate of self-renewal of Canadian goldenrod (Solidago canadensis L.) and giant goldenrod (S. gigantea Aiton), and the possibility of achieving full generative development on fallow land restored to agricultural use with mechanical treatments. The following research objects were examined: the control (no mechanical treatments); one-time mowing; two-time mowing; one-time mowing plus one-time rotary tilling; and one-time mowing plus two-time rotary tilling. The phenological development of Solidago spp. was observed every 14 days from June to September each year. In October of each growing season, the aboveground parts of goldenrods’ biomass were measured, and selected morphological parameters were assessed. Two-time mowing and one-time mowing with two-time rotary tilling resulted in the highest reductions in the share of goldenrods in the generative stages of development, of 64.0% and 51.7% compared to the control, respectively. The two-time mowing treatment was the most effective at inhibiting goldenrods’ biomass accumulation, with a 57.7–77.0% decrease in biomass compared to the control. This treatment also reduced the number of flowering shoots and inflorescence lengths of both Solidago species.

Cultivation of spring cereal mixtures (SCMs) is one of the ways to increase the yield of crops in mountainous areas of Poland. There are only a few current long-term studies on this topic. Our study aimed at analyzing yield and competitiveness as well as the economic indicators of spring cereals in pure or mixed sowings in integrated or organic crop rotations over nine years. A field experiment including pure sowings of oats, spring barley, or spring triticale and their two-component SCMs, each in two systems, organic and integrated crop rotation, was carried out in the Mountainous Experimental Station in Czyrna, Poland, in the years 2011–2019. On average, cereals in the pure sowings and mixtures yielded 18% lower in the organic rotations compared with the integrated ones. However, SCMs yielded higher than the pure sowings, and displayed a higher leaf area index and land equivalent ratio. The average gross margin without subsidies was almost two times higher in the organic crop rotations than in the integrated ones, which was influenced mainly by the cultivation of barley in pure sowing. Summing up, the cultivation of SCMs in the mountainous areas of southern Poland is advised because of both productive and economic factors.

Production of allelopathic substances is a factor determining the ecological success of invasive plants—Canadian goldenrod (S. canadensis L.) and giant goldenrod (S. gigantea Aiton). This research aimed at evaluating the autoallelopathic effect of aqueous extracts (AEs) prepared from various parts of Canadian goldenrod and giant goldenrod against vegetative growth, and biomass accumulation of both goldenrods. In the stage of 5–6 leaves, goldenrod plants, were foliar sprayed with AEs, at concentrations of 5 or 10%. The biochemical properties of AEs, i.e., total phenolic content, total antioxidant potential and selected plant hormones, were examined. Two and ten days after spraying (DAS), damages to aboveground parts of goldenrods (necrosis and wilting) were visually assessed. The fresh mass of above- and belowground parts of goldenrods were measured 21 DAS. AEs from various parts of Canadian goldenrod or giant goldenrod displayed autoallelopathic properties of inhibitory nature. The phytotoxic potential of AEs varied depending on their source. Canadian goldenrod was more susceptible to the AEs, manifested by more significant damages to aboveground parts and a greater decrease in above- and belowground biomass. The most effective against growth and development of Canadian goldenrod and giant goldenrod were AEs from rhizomes, which caused a reduction of fresh biomass of goldenrods up to 42%, compared to water-treated control.

Rye brome is a rare and nuisance weed in winter wheat canopies. In recent years, farmers have complained about the inadequate chemical control of this species. This study aimed to assess the effectiveness of seed meals obtained from allelopathic crops as an environmentally-friendly alternative for the control of herbicide-susceptible (S) and -resistant (R) rye brome biotypes in winter wheat. The pot experiment was conducted in a greenhouse at the Swojczyce Research and Training Station in Wrocław (Poland) to determine the impact of seed meals from: Fagopyrum esculentum, Sinapis alba, Phacelia tanacetifolia, Lupinus luteus, Raphanus sativus var. oleiformis and Ornithopus sativus, at 1 and 3% doses. Wheat emergence (>90%) and early growth were not affected by the presence in the soil of seed meals (only at 1% concentration) from P. tanacetifolia and R. sativus. The efficacy of these meals (reduction of aboveground biomass) at rye brome control was the same as the herbicide or higher. Seed meals from P. tanacetifolia reduced the emergence of the S and R biotypes by approximately 70 percentage points (p.p.) and 30 p.p., respectively, and limited the initial growth of both biotypes. Addition to soil meals from F. esculentum and R. sativus generally reduced only initial weed growth.