Current industrial herbicides have a negative impact on the environment and have widespread resistance, so computational studies on their properties, elimination, and overcoming resistance can be helpful. On the other hand, developing new herbicides, especially bioherbicides, is slow and costly. Therefore, computational studies that guide the design and search for new herbicides that exist in various plant sources, can alleviate the pain associated with the many obstacles. This review summarizes for the first time the most recent studies on both aspects of herbicides over 10 years.

Several Acacia species are aggressive invaders outside their native range, often occupying extensive areas. Traditional management approaches have proven to be ineffective and economically unfeasible, especially when dealing with large infestations. Here, we explain a different approach to complement traditional management by using the waste from Acacia management activities. This approach can provide stakeholders with tools to potentially reduce management costs and encourage proactive management actions. It also prioritizes potential applications of Acacia waste biomass for agriculture and forestry as a way of sequestering the carbon released during control actions. We advocate the use of compost/vermicompost, green manure and charcoal produced from Acacia waste, as several studies have shown their effectiveness in improving soil fertility and supporting crop growth. The use of waste and derivatives as bioherbicides or biostimulants is pending validation under field conditions. Although invasive Acacia spp. are banned from commercialization and cultivation, the use of their waste remains permissible. In this respect, we recommend the collection of Acacia waste during the vegetative stage and its subsequent use after being dried or when dead, to prevent further propagation. Moreover, it is crucial to establish a legal framework to mitigate potential risks associated with the handling and disposal of Acacia waste.

Biological control of undesirable weeds associated with crop cultivation is a sustainable approach that can reduce chemical herbicide dependence. The current study aimed to assess the bio-herbicidal potential of the donor species Ononis vaginalis Vahl. on germination efficiency as well as various growth and physiological parameters of the recipient species Rumex dentatus L., a major broad bean pest (Vicia faba L.). To assess the greatest inhibitory allelopathic effect on the recipient species in mixed (Rumex dentatus L. and Vicia faba L.) and pure cultures (each one separately), two experiments were conducted under laboratory conditions. A Petri dish experiment using O. vaginalis shoot aqueous extract (5%, 10%, 20%, and 40%) and a pot experiment using O. vaginalis shoot crude powder (1%, 2%, 5%, and 10%) were conducted to investigate its biological activity on some growth and physiological parameters of both crop and weed species. O. vaginalis underwent a general phytochemical screening that revealed a high production of allelochemicals, which are secondary metabolites and may have a function like that of natural herbicides. The result showed that the germination of V. faba seeds in both pure and mixed cultures was not significantly affected by low levels of O. vaginalis shoot aqueous extract treatments in pure and mixed cultures, in contrast, those recorded for R. dentatus gradually dropped as levels of O. vaginalis increased in both cultures. Results recorded a significant increase in total phenolics of V. faba shoots and roots under different treatments, except at the high concentrations of crude powder at the donor species level (5 and10%). A reduction in the total phenolic and flavonoid fractions was observed in R. dentatus roots under varying concentration treatments. Conversely, under high concentration treatments, flavonoids decreased in the roots of the mixed culture of R. dentatus but increased in the shoots. In conclusion, allelopathy can be used to suppress weeds in field crops. The study confirmed the use of O. vaginalis into current weed control techniques. O. vaginalis could be explored further for weed suppression in the field.

Among the alternatives to synthetic plant protection products, biocontrol appears as a promising method. This review reports on the diversity of fungal secondary metabolites phytotoxic to weeds and on the approach generally used to extract, characterize, identify and exploit them for weed management. The 183 phytotoxic fungal secondary metabolites discussed in this review fall into five main classes of molecules: 61 polyketides, 53 terpenoids, 36 nitrogenous metabolites, 18 phenols and phenolic acids, and 15 miscellaneous. They are mainly produced by the genera Drechslera, Fusarium and Alternaria. The phytotoxic effects, more often described by the symptoms they produce on plants than by their mode of action, range from inhibition of germination to inhibition of root and vegetative growth, including tissue and organ alterations. The biochemical characterization of fungal secondary metabolites requires expertise and tools to carry out fungal cultivation and metabolite extraction, phytotoxicity tests, purification and fractionation of the extracts, and chemical identification procedures. Phytotoxicity tests are mainly carried out under controlled laboratory conditions (not always on whole plants), while effectiveness against targeted weeds and environmental impacts must be assessed in greenhouses and open fields. These steps are necessary for the formulation of effective, environment-friendly fungal secondary metabolites-derived bioherbicides using new technologies such as nanomaterials. © 2023 Society of Chemical Industry.

This review aimed to show that bioherbicides are possible in organic agriculture as natural compounds from fungi and metabolites produced by them. It is discussed that new formulations must be developed to improve field stability and enable the commercialization of microbial herbicides. Due to these bottlenecks, it is crucial to advance the bioprocesses behind the formulation and fermentation of bio-based herbicides, scaling up, strategies for field application, and the potential of bioherbicides in the global market. In this sense, it proposed insights for modern agriculture based on sustainable development and circular economy, precisely the formulation, scale-up, and field application of microbial bioherbicides.

Radicinin is a phytotoxic dihydropyranopyran-4,5-dione isolated from the culture filtrates of Cochliobolus australiensis, a phytopathogenic fungus of the invasive weed buffelgrass (Cenchrus ciliaris). Radicinin proved to have interesting potential as a natural herbicide. Being interested in elucidating the mechanism of action and considering radicinin is produced in small quantities by C. australiensis, we opted to use (±)-3-deoxyradicinin, a synthetic analogue of radicinin that is available in larger quantities and shows radicinin-like phytotoxic activities. To obtain information about subcellular targets and mechanism(s) of action of the toxin, the study was carried out by using tomato (Solanum lycopersicum L.), which, apart from its economic relevance, has become a model plant species for physiological and molecular studies. Results of biochemical assays showed that (±)-3-deoxyradicinin administration to leaves induced chlorosis, ion leakage, hydrogen peroxide production, and membrane lipid peroxidation. Remarkably, the compound determined the uncontrolled opening of stomata, which, in turn, resulted in plant wilting. Confocal microscopy analysis of protoplasts treated with (±)-3-deoxyradicinin ascertained that the toxin targeted chloroplasts, eliciting an overproduction of reactive singlet oxygen species. This oxidative stress status was related by qRT-PCR experiments to the activation of transcription of genes of a chloroplast-specific pathway of programmed cell death.

Weeds such as parasite plants are one of the most serious pests that farmers are forced to combat since the development of agriculture using different methods including mechanic and agronomy strategies. These pests have generated significant losses of agrarian and herding production, constituting a serious impediment for agricultural activities in reforestation practices and in important infrastructures. All these serious problems have induced the expansive and massive use of synthetic herbicides, which represents one of the main cause of environmental pollution, as well as serious risks for human and animal health. An alternative environmental friendly control method could be the use of bioherbicides based on suitably bioformulated natural products, of which the main ones are fungal phytotoxins. This review covers the literature from 1980 to the present (2022) and concerns fungal phytotoxins with potential herbicidal activity in order to obtain their efficacy as bioherbicides for practical application in agriculture. Furthermore, some bioherbicides based on microbial toxic metabolites are commercially available, and their application in field, mode of action and future perspectives are also discussed.

Soil plays a primary role in the activity of plant allelochemicals in natural and agricultural systems. In this work, we compared the phytotoxicity of three natural hydroxycoumarins (umbelliferone, esculetin, and scopoletin) to different model plant species (Lactuca sativa, Eruca sativa, and Hordeum vulgare) in Petri dishes, and then selected the most phytotoxic compound (umbelliferone) to assess how its adsorption and dissipation in two distinct soils affected the expression of its phytotoxic activity. The root growth inhibitory effect of umbelliferone was significantly greater than that of esculetin and scopoletin, and the dicot species (L. sativa and E. sativa) were more sensitive to the hydroxycoumarins than the monocot species (H. vulgare). For all three plant species tested, the phytotoxicity of umbelliferone decreased in the following order: soilless (Petri dishes) > soil 1 > soil 2. In soil 2 (alkaline), umbelliferone displayed negligible adsorption (Kf < 0.01) and rapid biodegradation (t1/2 = 0.2-0.8 days), and its phytotoxicity was barely expressed. In soil 1 (acid), umbelliferone displayed enhanced adsorption (Kf = 2.94), slower biodegradation (t1/2 = 1.5-2.1 days), and its phytotoxicity was better expressed than in soil 2. When the microbial activity of soil 2 was suppressed by autoclaving, the phytotoxicity of umbelliferone, in the presence of soil, became similar to that observed under soilless conditions. The results illustrate how soil processes can reduce the allelopathic activity of hydroxycoumarins in natural and agricultural ecosystems, and suggest scenarios where the bioactivity of hydroxycoumarins may be better expressed.

This is the first study to evaluate the phytotoxic activity of three phenolic compounds present in the essential oil of the labdanum of Cistus ladanifer, an allelopathic species of the Mediterranean ecosystem. Propiophenone, 4\'-methylacetophenone, and 2\',4\'-dimethylacetophenone slightly inhibit total germination and radicle growth of Lactuca sativa, and they strongly delay germination and reduce hypocotyl size. On the other hand, the inhibition effect of these compounds on Allium cepa was stronger on total germination than on germination rate, and radicle length compared to hypocotyl size. The position and number of methyl groups will affect the efficacy of the derivative. 2\',4\'-dimethylacetophenone was the most phytotoxic compound. The activity of the compounds depended on their concentration and presented hormetic effects. In L. sativa, on paper, propiophenone presented greater inhibition of hypocotyl size at greater concentrations, with IC50 = 0.1 mM, whereas 4\'-methylacetophenone obtained IC50 = 0.4 mM for germination rate. When the mixture of the three compounds was applied, in L. sativa, on paper, the inhibition effect on total germination and the germination rate was significantly greater compared to the effect of the compounds when they were applied separately; moreover, the mixture inhibited radicle growth, whereas propiophenone and 4\'-methylacetophenone did not exert such effect when applied separately. The activity of the pure compounds and that of the mixture also changed based on the substrate used. When the trial was conducted in soil, the separate compounds delayed the germination of the A. cepa to a greater extent compared to the trial on paper, although they stimulated seedling growth. In soil, L. sativa against 4\'-methylacetophenone also showed the opposite effect at low concentrations (0.1 mM), with stimulation of germination rate, whereas propiophenone and 4\'-methylacetophenone presented a slightly increased effect.

Plant pathogens with a broad host range are commercially more attractive as microbial bioherbicides than strictly host-specific pathogens as a result of the wider market potential of a product capable of controlling multiple species. However, the perceived spatiotemporal disease risk to nontarget plants is a barrier to their adoption for weed control. We consider two approaches to managing this risk. First, we consider safety zones and withholding periods for bioherbicide treatment sites. These must ensure inoculum spreading from, or surviving at the site, exposes nontarget plants to no more inoculum than from natural sources. They can be determined using simple dispersal models. We show that a ratio of added:natural inoculum of 1.0 is biologically reasonable as an \'acceptable risk\' and a sound basis for safety zones and withholding periods. These would be analogous to the \'conditions of use\' for synthetic chemical herbicides aimed at minimizing collateral damage to susceptible plants from spray drift and persistent soil residues. Second, weed-specific isolates of broad host-range pathogens may avoid the need for safety zones and withholding periods. Such isolates have been found in many broad host-range pathogen species. Their utilization as bioherbicides may more easily meet the requirements of regulators. Mixtures of different weed-specific isolates of a pathogen could provide bioherbicides with commercially attractive spectrums of weed control activity. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.