Weeds can be one of the most severe threats to crop production, especially when they are widespread and highly adaptable. Part of the adaptive strategy of plants is the ability to germinate in different conditions. Germination is the first developmental phase of plant life and is fundamental for its establishment. In this work, the germination of two populations of Datura stramonium L. at two different sites in Croatia (one cropped, the other non-agricultural) was tested under a wide range of salinity stress, 4, 8, 12, and 16 dS/m, and pH stress, values 1–9, at two temperature ranges of 15–25 °C and 18–30 °C. The results show that this species can tolerate high salinity, with a high number of seeds germinating, even under the highest level of saline stress and especially at higher temperatures: 21.7% of seeds germinated at 15–25 °C and 51.2% at 18–30 °C. D. stramonium also appears to be quite acid tolerant, with a significant reduction in germination only at pH 2, and no germination only at pH 1. Germination was always higher at higher temperatures, independently of abiotic stress. Although there were some differences between the two populations in the final germination percentages, they were similar in their responses to the abiotic stresses.

With the increasing demand for non-chemical weed control methods, phenolic acids have shown promise due to their natural weed inhibitory potential. In this study, the inhibitory effect of ferulic acid, vanillic acid and p-coumaric acid was investigated on Ambrosia artemisiifolia L. and the selectivity of Zea mays L. against these phenolic acids was tested. The seeds of A. artemisiifolia and Z. mays were treated in vitro with three phenolic acids at doses of 200–600 × 10⁻⁷ mol and in vivo foliar on A. artemisiifolia and Z. mays plants. While all phenolic acids had effects on the early growth of A. artemisiifolia, p-coumaric acid significantly reduced the length of radicle and hypocotyl by more than 60% while the effects on Z. mays were minimal. In vivo assessments using chlorophyll fluorescence and multispectral imaging showed selective stress responses in A. artemisiifolia but not in Z. mays after foliar application. The in vitro results show that p-coumaric acid is a promising compound for the control of A. artemisiifolia. However, these phenolic acids at these doses led to an insufficient reduction in photochemical efficiency. Therefore, these natural compounds need to be combined with other methods of weed control.

Herbicides are the most commonly used means of controlling the growth of Ambrosia artemisiifolia L. Their constant use has led to the development of resistant populations. They can be evaluated by studying seed germination and the corresponding grown plants, but A. artemisiifolia exhibits seed dormancy, preventing germination and delaying research. Here, we developed a simple and rapid method to stimulate germination of freshly collected or stored A. artemisiifolia seeds. The germination of A. artemisiifolia freshly collected/stored seeds was evaluated after storage, stratification, and chemical treatments (ethephon, gibberellic acid (GA₃), thiourea, KNO₃). Ethephon or ethephon + GA₃ improved freshly collected seed germination by 88 and 95%, respectively, and germination of stored seeds by 78 and 80%, respectively. In addition, placing the seeds of A. artemisiifolia in ethephon, GA₃, ethephon + GA₃, or thiourea solutions caused the freshly collected seeds to germinate faster than stored seeds or nontreated seeds. In contrast, the conditioning of seeds in these solutions favored germination of stored seeds, especially when ethephon + GA₃ or GA₃ was used. Imbibition of the freshly collected A. artemisiifolia seeds in a mixture of ethephon and GA₃ can effectively overcome primary dormancy when rapid experimental results are needed. For seeds requiring prolonged storage, conditioning in ethephon, GA₃, or thiourea solutions may be applied to promote germination.

The aim of this in vitro study was to investigate the effects of six phenolic acids applied individually and in combination at concentrations of 0–20 mM on Ambrosia artemisiifolia and soil bacteria. Chlorogenic acid (CGA), p-hydroxybenzoic acid (PHBA), and protocatechuic acid (PKA) were tested on both plants and bacteria, whereas p-coumaric (PCA), vanillic (VA), and ferulic (FA) acids were tested only on soil bacteria. The estimated EC₅₀ for radicle inhibition were 4.9 ± 0.1 mM for PHBA, 4.1 ± 0.7 mM for CGA, 6.6 ± 0.7 mM for PKA, 10.1 ± 0.9 mM for CGA + PHBA + PKA, 4.6 ± 0.4 mM for ferulic, vanillic, and p-coumaric acids (FA + VA + PCA), and 2.5 ± 0.3 mM for the combination of all six phenolic acids. Bacterial strains were less susceptible to individual phenolic acids compared to their combinations. PKA and CGA showed the strongest antibacterial activity, with PKA inhibiting 78% and killing 74% of strains at ≤10 mM, while CGA inhibited 61% and killed 57%. Conversely, PCA and VA had the weakest antibacterial effects, requiring ≥20 mM for complete inhibition. Among test genera, Stenotrophomonas, Bacillus, Peribacillus, and Pseudomonas were more susceptible than Enterobacter and Lelliottia. Subinhibitory concentrations of individual phenolic acids did not affect bacterial motility, except for PKA. The study suggests that VA, PCA and FA alone or combined and PHBA alone, appear promising for weed management. Reduced herbicide strategies may safely incorporate CGA and PKA at concentrations below 2.5 mM.

Heat disinfection of soil can be used to reduce the content of the soil seedbank. However, species differ in the lethal temperature needed for seed destruction and mortality. Laboratory research was conducted on the seeds of two weed species, redroot pigweed (Amaranthus retroflexus L.) and yellow foxtail [Setaria pumila (Poir.) Roem. & Schult]. The soil samples were collected at the experimental station Šašinovečki Lug, Zagreb, Croatia (45.850289°N, 16.180465°E), and exposed to linearly increasing constant temperatures of 40, 50, 60, 80, 100, and 120 C and exposure times of 30, 60, and 90 min in a laboratory oven. Weed seeds were then extracted from the soil using the sieve separation method and survival was measured by germinating seeds on filter paper. Germination counts were converted into percentages of mortality compared with untreated seeds. The results show that both temperature and exposure time significantly affected seed mortality of both weed species. Amaranthus retroflexus shows a greater susceptibility to high temperatures than S. pumila. A fitted three-parameter sigmoid model was used to define the relationship between temperature and exposure time needed for 50% (LT₅₀) and 90% (LT₉₀) seed mortality. The estimated LT₅₀ values for A. retroflexus are 58.89 to 46.08 C over the 30- to 90-min exposure times; the estimated LT₉₀ values were 113.36 to 65.72 C for the same durations. The estimated LT₅₀ values for S. pumila over the 30- to 90-min exposure times ranged from 91.33 to 75.15 C; the estimated LT₉₀ ranged from 98.79 to 90.32 C over the same durations. The research results contribute to the knowledge about the thermal sensitivity of seeds. Estimating efficacy of soil-heating treatments is essential when comparing the environmental, economic, and social costs of alternatives to conventional weed control methods.