This study aimed to investigate whether different doses of specific phenolic acids (chlorogenic acid, caffeic acid, ferulic acid, gallic acid, protocatechuic acid, p-hydroxybenzoic acid, syringic acid, vanillic acid, and p-coumaric acid), alone or in combination, can inhibit the early growth of the common ragweed (Ambrosia artemisiifolia L., Asterales: Asteraceae). A seed bioassay was performed in Petri dishes and placed in a climate chamber to assess the effects of five dose levels of phenolic acids to radicle and shoot length, as well seedling biomass of A. artemisiifolia. The lowest dose of phenolic acid corresponded to the natural phenolic acid concentration previously reported in dry plant tissue samples from Brassicaceae cover crop plants. Results show that the inhibition of the early growth of A. artemisiifolia depends strongly on phenolic acid. Across different treatments, high doses of phenolic acids significantly shortened shoots and radicles, as well as reduced seedling biomass. Treating seeds with ferulic acid alone, vanillic acid alone, p-hydroxybenzoic acid alone, or a mixture of all phenolic acids significantly reduced all early growth parameters. The estimated effective dose for the 50% inhibition (ED50) of radicle growth in A. artemisiifolia seedlings was 368.39 ± 59.85 × 10−8 mol with ferulic acid, 135.41 ± 17.65 × 10−8 mol with p-coumaric acid, 810.36 ± 134.15 × 10−8 mol with p-hydroxybenzoic acid, and 160.11 ± 12.30 × 10−8 mol with the combination of all phenolic acids.

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.

Soil pH can affect the adsorption of mesotrione and exacerbate crop injury under non-acidic conditions. Soil samples collected from the same location were irrigated with water solutions of pH 7.5, 6.5, 5.5, and 4.5 and treated with 72, 36, 24, 18, 9, 4.5, 2.3, and 1.1 g a.i. (active ingredient) of mesotrione/ha. Bean growth was monitored over 28 days. Soil pH solution did not influence the effect of mesotrione on plant fresh weight, while herbicide-induced visual injury and reduction in carotenoid content were significantly mitigated under acidic conditions. The lowest rate (1.1 g a.i./ha) applied in slightly acidic soil (pH 6.5) caused visual injury of 45% 28 days after treatment, while visual injuries on plants grown in soils with pH 4.5 were only 20%. Further, bean plants grown at pH 4.5 showed only 3.3% lower carotenoid content compared to control plants since for those grown in a slightly alkaline environment (pH 7.5) reduction of this pigment was 35.5%. The mean effective dose (ED50 ± standard error) of mesotrione for inhibition of carotenoids were 5.25 ± 0.61 g a.i./ha at pH 7.5, 9.57 ± 0.74 g a.i./ha at pH 6.5, 13.07 ± 0.91 g a.i./ha at pH 5.5, and 14.98 ± 0.94 g a.i./ha at pH 4.5. Results indicate that the common bean is highly susceptible to the presence of mesotrione residue and that this sensitivity strongly depends on soil pH solution.

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.