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Sorghum (Sorghum bicolor (L.) Moench) is one of the globally important cereal crops well adapted to Sub-Saharan Africa (SSA) agro-ecology. However, the productivity of sorghum is hindered by both abiotic and biotic factors including drought, Striga, insect pests, poor soil fertility, and diseases. Among the constraints, Striga (genus), also called witch weed, is the most important production problem in the area. Although there have been various control methods practiced for years, none of these have been practically effective in eradicating Striga, neither are they easily accessible for small holder farmers, while some are also not environmentally friendly. Therefore, this study was designed with the objective of identifying potential Striga suppressing rhizobacteria associated with sorghum. Treatment of S. hermonthica seeds with isolates E19G12, E29G2b and E19G10 resulted in the lowest S. hermonthica seed germination of 0%, 1%, and 2.7% respectively, which were significantly lower than any of the treatments. Mean germination percentage ranged from 9 to 59.7 and 0 to 27 in the absence and presence of host plants, respectively. The results showed a statistically significant germination inhibition (p < 0.001). Finally, the most effective isolates were shortlisted, E19G6a, E19G9, E19G6b, E19G10, E19B, E19G12, E29G2a, and E29G7 were morphologically and biochemically identified to belong to the genera of Pseudomonas, Klebssiella, Bacillus and Entrobacter. The results of the study demonstrated the existence of promising soil-borne bacteria that could be exploited as bioherbicides to control Striga infestation on sorghum provided that broader samples from various parts of the country are explored.

The role of microbial communities in the establishment of plant pathogens introduced to new environments as weed biocontrol agents is relatively unexplored. Substantial evidence from crop protection research shows how bulk microbial communities influence the establishment, survival, and success of pathogens. Just as mismatches between biocontrol agents, host genotypes, and climate can lead to establishment failure, we propose that mismatches between microbial biocontrol agents and resident microbiomes may be a cause of apparent weed biocontrol failures. From this perspective, we discuss recent progress in research on plant-associated microbial communities whose interactions influence disease development, or “pathobiomes,” and consider the implications for biocontrol agent evaluation and release. Open questions about how weed pathobiomes develop and influence agent success rates provide ample opportunity for researchers to adapt new methods and analytical frameworks that will enhance biocontrol programs. We conclude by prioritizing the development of standard methods to include microbiomes as a component of release studies. Developing a pathobiome-aware agent selection and release process will improve agent establishment rates and biocontrol outcomes.

This article offers a critical analysis of the evolution of encapsulation methods for herbicides and natural products, with a main focus on organic formulations. It extols the possibilities presented by these micro- and nanomaterials, such as their slow release, stability, bioavailability, water solubility, and stability for classical and natural herbicides from their origins to the present. [ABSTRACT FROM AUTHOR]

Biological control refers to the use of living beneficial organisms as well as the products of their metabolism in pest control. Weed plants are indispensable companions of cultivated plants, in which they cause substantial damage. Organic food production, human health care and environmental preservation impose a need for the production and application of bioherbicides, particularly in organic systems of plant production. Plant pathogens have significant potential as biological agents in weed control. The aim of the present study was to indicate the most important properties of the weed biological control system, with particular emphasis on the use of fungi-based bioherbicides. According to the organism they suppress, biopesticides are classified into bioinsecticides, biofungicides, bioherbicides, etc. Weed control using plant pathogens can be performed in three ways, by classical, conservation and augmentative biological control. Bioherbicides were initially introduced to the market in 1980, and the majority of them were fungi-based bioherbicides. The most common fungi included in bioherbicides belong to the genera Alternaria, Colletotrichum, Cercospora, Fusarium, Phomopsis, Phytophthora, Phoma, Puccinia, etc. The studies, development and final commercialisation of fungi as biological control agents face many obstacles, ranging from basic biological facts to social and economic factors. There are also challenges in the production, formulation process, environmental friendliness, duration of herbicidal action, and expensive and time-consuming registration procedures. Considering the success in weed suppression with fungi-based bioherbicides, the global market is still dominated by chemical companies manufacturing synthetic herbicides, while there are no such products on the Serbian market yet.

The sustainable management of the environment and crop production in modern agriculture involves dealing with challenges from climate change, environmental pollution, depletion of natural resources, as well as pressure to cope with dependence on agricultural inputs. Balancing crop productivity with environmental sustainability is one of the main challenges for agriculture worldwide. The emergence of weeds resistant to synthetic herbicides generates huge economic losses, so unconventional weed control strategies, especially those based on ecological principles, are very much needed in modern agriculture. Incorporating a natural eco-friendly approach—allelopathy—as a tool in an integrated weed control plan by growing specific crops or spraying fields with extracts containing allelopathic compounds can significantly reduce the use of herbicides. Allelopathy is considered a multi-dimensional phenomenon occurring constantly in natural and anthropogenic ecosystems, by which one organism produces biochemicals that influence the growth, survival, development, and reproduction of other organisms. The objective of this systematic literature review is to present a comprehensive overview of allelopathy, define this phenomenon, and classify allelochemicals. This paper also discusses and highlights recent advances, ongoing research, and prospects on plant allelopathy management practices applied in agriculture, and the underlying allelopathic mechanisms. The review suggested the holistic view of some allelochemicals as an ecological approach to integrated weed control and is an important contribution to future research directions of multidisciplinary programs, chemoinformatic tools, and novel biotechnology methods to plant breeding. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In recent years, interest in natural products with herbicidal activity as new tools for integrated weed management has increased. The European Union is demanding a reduction in the number of herbicides used, forbidding use of the most toxic ones, despite the problem of weed resistance increasing. Pelargonic acid (PA) is the only natural herbicide available in Spain. In this work, two field assays were performed with the natural compounds carvacrol (CAR), citral (CIT), eugenol (EUG), thymol (THY), p-cymene (P-CYM), (PA), and the combination of PA with CIT—all except P-CYM formulated by Seipasa—to test their herbicidal efficacy in real conditions. They were compared with commercial PA, glyphosate (GLY) and oxyfluorfen (OXY). In both experiments, GLY achieved the best weed control. Considering the natural herbicides, PA formulated by Seipasa and PA plus CIT were the most effective. From both experiments, some conclusions can be extracted for better herbicidal performance of natural products: (1) use products on sensitive weed species, (2) treat weeds at earlier phenological stages, (3) find the active doses in field conditions, (4) cover weeds well when treating, (5) ensure adequate formulation of products, and (6) develop a strategy for correct application.

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. [ABSTRACT FROM AUTHOR]

Over the past few years, both producers and consumers have become increasingly interested in organic farming because conventional agriculture relies so heavily on the use of synthetic pesticides, thus causing environmental pollution. Weeds, as inevitable "companions" of cultivated plants, represent a major, everlasting issue in plant production. As organic plant production is legally regulated, the control of undesirable plants such as weeds is further complicated. Using the relevant literature, the purpose of this study is to survey the existing weed control methods in organic crop production. In order to be certified, organic plants have to be grown in the farming system without the application of synthetic herbicides and other chemicals that are commonly used in conventional production. This means that crop growers have to apply non-chemical, alternative methods of weed suppression, i.e. weed control based on the combination of cropping practices, mechanical control, and the use of bioherbicides. There is a large number of plant extracts with bioherbicidal activity, the effect of which is mostly attributed to the biological phenomenon of allelopathy, rendering such weed control sustainable, inexpensive, and environmentally friendly. Although bioherbicides are successfully used in organic farming worldwide, there are no registered bioherbicides in Serbia to date (according to the data of the Ministry of Agriculture, Forestry and Water Management of the Republic of Serbia). Both organic producers and experts should raise awareness of the importance of successful weed control to the health of cultivated plants, soil, beneficial organisms, and the entire ecosystem, which requires further research attention.

Allelopathic effects of different plant allelochemicals have become the focus of studies that aim to determine new pesticidal compounds. Plant extracts with different chemical compositions can be obtained using different methods of extraction, whereas studies dealing with allelopathic properties use biotests to obtain fast and precise results. Such studies were undertaken after noticing the allelopathic effects of industrial hemp (Cannabis sativa L.) on the surrounding crops. Trials that involve the application of hemp extracts obtained by different methods resulted in determining the hemp allelopathic effects on Stellaria media (L.)Scop., Beta vulgaris ssp. vulgaris var. vulgaris, Lupinus albus L., corn (Zea mays L.), Cyperus rotundus L., Matricaria recutita L., Lepidium sativum L., lettuce (Lactuca sativa L.), rapeseed (Brassica napus L.), wheat (Triticum aestivum L.), rye (Secale cereal M. Bieb.), Ambrosia artemisiifolia L., Chenopodium album L., and Sorghum halepense L..

This article offers a critical analysis of the evolution of encapsulation methods for herbicides and natural products, with a main focus on organic formulations. It extols the possibilities presented by these micro- and nanomaterials, such as their slow release, stability, bioavailability, water solubility, and stability for classical and natural herbicides from their origins to the present.

Prosopis juliflora (Sw.) DC. Is highly recognized for its invasive character and its detrimental effects on different plant species across the world. In this study, a field survey was performed to assess the impact of P. juliflora on the surrounding native plants, followed by the effect of different concentrations of its aqueous leaf extract on seed germination and seedling growth of selected Qatari flora. Our field observations indicated a high prevalence of new recruitments of P. juliflora than other native-associated plants in the study site. Germination percentage and/or seed radicle length of the test species: Acacia tortilis (Forssk.) Hayne, Prosopis cineraria (L.) Druce, Sueda aegyptica (Hasselq.) Aellen, Halopeplis perfoliata (Forssk.) Bunge ex Schweinf. & Asch, and P. juliflora were significantly (p ≤ 0.05) reduced by the extracts at different concentration levels. Moreover, the germination rate of A. tortilis was not affected; however, the seed germination of P. cineraria was significantly affected at concentrations of 6 and 8 mg mL−1. The seed radicle lengths at 2 mg mL−1 were significantly reduced for both plant species. The seed germination and radicle length of S. aegyptica and H. perfoliata were significantly decreased at 2 mg mL−1 of extract of P. juliflora. Furthermore, the height and biomass of the seedlings of Aeluropus lagopoides (L.) Trin. ex Thwaites, Caroxylon imbricatum (Forssk.), and Tetraena qatarensis (Hadidi) Beier & Thulin were significantly reduced by the aqueous extracts at 6 and 8 mg mL−1. The aqueous extract reduced the seed germination and seedling growth at 6 and 8 mg mL−1, indicating an autotoxic effect. Such allelopathic behavior of P. juliflora designates the potential investigation of using its allelochemicals as naturally based herbicides in agrosystems.

Essential oils produced by plants, and their components, could be sources of new natural herbicidal compounds. Thirteen oils extracted from six wild Lamiaceae species (namely Clinopodium suaveolens (Sm.) Kuntze, Satureja montana L. subsp. montana, Thymbra capitata (L.) Cav., Salvia fruticosa Mill. subsp. thomasii (Lacaita) Brullo, Guglielmo, Pavone & Terrasi, Satureja cuneifolia Ten., and Thymus spinulosus Ten.) from South Italy were tested in vitro for the phytotoxic activity to cress and branched broomrape seeds, tomato radicles, and lambsquarters leaf disks. Moreover, the possible correlation between oil composition and biological activity was evaluated. One of the oils from T. capitata inhibited cress germination by 96.4% at the lowest tested concentration (100 ppm) and reduced both chlorophyll and carotenoid content in lambsquarters leaf disks by around 50%. Some oils, particularly those from T. spinulosus, inhibited tomato radicle elongation by 85% at 1000 ppm. Many oils inhibited broomrape seed germination up to 100% when tested in solution at 1000 ppm or released as vapors. Among the oil components, α-terpinene, p-cymene, β-cis-ocimene, cis-sabinene hydrate, carvacrol methyl ether, and thymol were mostly correlated to the inhibition of cress seeds germination and tomato radicle elongation. The presence of thymol and p-cymene was also correlated to the inhibition of broomrape seed germination. Some of the tested essential oils or their components could have potential as pre-emergence herbicides and could be useful in the development of new weed control strategies.

Pelargonic acid is a non-selective post-emergence contact bio-herbicide which is registered both for cropping and non-cropping uses in several countries. Dose–response curves on the efficacy of pelargonic acid against common weeds in Mediterranean areas are not available. Dose–response curves of pelargonic acid efficacy against summer and winter annual weeds were evaluated in two field experiments (winter exp. in 2019 and summer exp. in 2020) in central Italy. Pelargonic acid was applied at five doses (1.4, 2.7, 5.4, 10.9 and 21.8 kg a.i. ha−1). Data on weed density, weed dry weight, and weed ground cover were used to calculate the efficacy of pelargonic acid against winter and summer weeds. Data were subjected to a non-linear regression analysis using the logistic dose–response model. Dose of pelargonic acid required to obtain 50%, 70%, 90% and 95% weed control against each weed species (ED50, ED70, ED90 and ED95) were estimated. ED values allowed us to classify winter and summer weeds with respect to their susceptibility to pelargonic acid (ED50 values in kg ha−1 are reported in parenthesis): Kickxia spuria (2.6) (more susceptible) > Heliotropium europaeum (3.0) > Echinochloa crus-galli (3.4) > Solanum nigrum (3.6) > Stachys annua (5.3) > Papaver rhoeas (6.5) > Veronica hederifolia (10.3) > Amaranthus retroflexus (11.4) > Matricaria chamomilla (11.6) > Portulaca oleracea (18.7) > Lolium multiflorum (>21.8) (less susceptible). These findings will allow for the optimization of weed control by pelargonic acid and its use in weed management strategies, both in organic and sustainable cropping systems, under different environmental conditions.

Cover crops and mulches have become an alternative for soil management in vineyards due to the agronomic, environmental, and economic advantages, especially the possibility of weed control. Implicitly to this objective lies the idea of assessing the potential herbicide effect of the allelochemicals released by different cover crop and mulch species. With this objective, the present work evaluated the phytotoxic effects of 12 aqueous extracts of selected species with potential use as a cover crop or mulch: a Bromus species mixture (B. hordeaceus L. and B. rubens L.), Festuca arundinacea Schreb., Hordeum murinum L., H. vulgare L., Vulpia ciliata Dumort., Medicago rugosa Desr., M. sativa L., Trifolium subterraneum L., T. incarnatum L., Phacelia tanacetifolia Benth., Sinapis alba L., and Pinus sylvestris L.,on the germination and early growth of three troublesome weeds (Conyza bonariensis (L.) Cronquist, Aster squamatus (Spreng.) Hieron, and Bassia scoparia (L.) A. J.). The different in vitro bioassays showed that aqueous extracts of some species significantly inhibited or reduced germination and root and shoot growth of the target weed species in a dose-response manner. Germination of A. squamatus and C. bonariensis was reduced by 100-80% by the different extracts applied at 50% concentration, and completely blocked at 100% concentration, except for M rugosa extract to which both species showed less sensitivity. Root elongation of A. squamatus was absolutely inhibited under every extract and concentration, whereas C. bonariensis root growth showed only some tolerance to the crude extracts of F. arundinaceaand P. sylvestris. Bassia scoparia was relatively tolerant to the aqueous plant extracts, except for T. subterraneum crude extract, which reduced total germination by 80%; otherwise, B. scoparia showed higher general sensitivity of shoot growth than the other two weed species. The chemical profiles of phenolic compounds of the aqueous extracts were obtained and identified by HPLC-DAD, the phenolic profiles of H. murinum, V. ciliata, and M. rugosa being reported in this work for the first time. Using stepwise regression, the influence of certain phenolic compounds from the aqueous extracts on the germination and early growth of weeds was predicted. Among other significant compounds, the flavonoid naringenin identified in T. subterraneumaqueous extract at 8.09 µg·mL-1 was predicted to underlie its specific phytotoxicity on B. scoparia germination. These results support the use of cover crops and mulches in weed management and can help to select the most suitable species to adopt according to the target weed species. Highlights • The phytotoxic nature of the aqueous extracts of twelve conventional and novel cover crops and mulch species was demonstrated on three troublesome weed species in vineyards. • Phenolic acids and flavonoids of the twelve aqueous extracts were identified and quantified by HPLC-DAD, and, by regression analysis, some allelochemicals were postulated as responsible for the phytotoxic effects. • The water-soluble phenolic profiles of three potential cover crops, namely Hordeum murinum, Vulpia ciliata, and Medicago rugosa, are reported for the first time. • In vitro germination and early root growth of Conyza bonariensis and Aster squamatus were almost entirely restricted by any of the twelve plants' aqueous extracts and presumably by the joint action of their particular allelopathic compounds. • Bassia scoparia germination was relatively much less sensitive to the extracts, except for Trifolium subterraneum, for which the flavonoid naringenin was predicted to underlie its specific phytotoxicity.

Bioherbicides are naturally originated products posing alternatives to synthetic herbicides for weed control. The objective of this study was to evaluate the efficacy of pelargonic acid and microencapsulated caraway essential oil on barnyardgrass (Echinochloa crus-galli (L.) P.Beauv.) and johnsongrass (Sorghum halepense (L.) Pers.). Two separate pot experiments were conducted at the Agricultural University of Athens (spring 2021), arranged in a completely randomized design (CRD) with six weed control treatments replicated four times. Treatments included the applications of: microencapsulated caraway essential oil at 50 g L−1 (CAR), CAR plus a commercial adjuvant (CAR + adj), i.e., alcohol ethoxylate at 1.8 g L−1, pelargonic acid at 36.3 g L−1 (PA), PA plus a commercial adjuvant (PA + adj), i.e., alcohol ethoxylate at 1.8 g L−1, and a tank mixture of pelargonic acid at 64 g L−1 plus microencapsulated caraway essential oil at 50 g L−1 (PA + CAR). An untreated control (CON) was also included. The results of the current research confirmed the knock-down effect of pelargonic acid against both barnyardgrass and johnsongrass and demonstrated the low efficacy of caraway microcapsules. The addition of a commercial adjuvant improved the efficacy of caraway essential oil but did not appear to affect the performance of pelargonic acid. No synergistic effects were observed between pelargonic acid and microencapsulated caraway essential oil. Further research is needed to optimize the use of these and other natural herbicides for weed control in agriculture and as components of sustainable integrated weed management (IWM) systems.

Meeting the nutritional needs of a dynamically developing global society is a major challenge. Despite the modernisation of agriculture, huge losses in the quality and quantity of crops occur each year, mainly due to weed species, which are the most important biotic limitation to agricultural production. Globally, approximately 1800 weed species cause a 31.5% reduction in plant production, which translates to USD 32 billion per year in economic losses. However, when the same herbicides are frequently applied, plants develop segetal immune mechanisms. There are currently around 380 herbicide-resistant weed biotypes worldwide. Due to the negative influence of herbicides on ecosystems and the legal regulations that limit the use of chemical crop protection products, it is necessary to develop a new method of weed control. Bioherbicides, based on living organisms or their secondary metabolites, seem to be an ideal solution. The biocontrol market is worth around EUR 550 million in Europe and EUR 1.6 billion worldwide, with an estimated 15% growth expected by 2025. Despite numerous studies that have demonstrated the effectiveness of microbial bioherbicides, only 25 mould-based bioherbicides are currently available to growers. Due to the high specificity and selectivity of biological crop protection products, as well as their low production costs and non-toxicity to the environment and human health, they would appear to be a safe alternative to chemical pesticides.

The continued and extensive use of synthetic herbicides to control weeds to maximize crop yield is no longer sustainable, as it results in negative impacts on the environment and human health. Innovative sustainable and resilient food production systems should preserve resources and environmental health by incorporating alternative natural herbicides, recycling waste, and favoring a circular economy. The present work assesses the value of different organic waste (Urtica dioica residues, Vicia faba pods, spent coffee grounds, and corn cobs) as bioherbicides and fertilizers in different seasons through pot and field two-year sequential experiments. Pot assays revealed that V. faba pods, spent coffee grounds, and corn cob waste showed the best inhibitory effect, which were subsequently evaluated in the Spring–Summer and Autumn crops. In the field, spent coffee grounds reduced the biomass of total naturally-emerged weeds and stimulated crop growth under scarce rainfall and warm days. However, its effect varied under different environmental conditions. Spent coffee grounds can partially control weeds in the field, which valorizes them as a bioherbicide and boosts sustainable agriculture.

A large number of studies of Cistus ladanifer highlight this Mediterranean shrub as a source of the phenolic compounds responsible for the allelopathic potential of this species. There are few phenolic compounds present in C. ladanifer that have not yet been studied. The objective of this work was to evaluate the activity of estragole and 2-isopropylphenol on filter paper and soil on monocotyledons (Allium cepa) and dicotyledons (Lactuca sativa). The results showed that when the test was carried out on paper, the germination and the growth of the L. sativa was strongly inhibited by 2 isopropylphenol and estragole. 2 isopropylphenol showed an IC50 on the germination of 0.7 mM and 0.1 mM on the germination rate, 0.4 mM on the size of radicle and 0.3 mM on the size of hypocotyl. Estragole showed an IC50 on the germination rate of 1.5 mM and 1.1 mM on the size of hypocotyl. The effects of these pure compounds on A. cepa were lower, and when the assays were performed on the soil, they were dissipated. The mixture of these compounds on A. cepa had 0.6 mM IC50 for the length hypocotyl on paper and 1.1 mM for the length of the radicle on soil. The mixture on L. sativa also inhibited the length of the radicle with an IC50 of 0.6 mM. On the other hand, it was also observed that estragole stimulated the growth of the A. cepa radicle length on soil, showing a hormetic effect with an EC50 of 0.1 mM. In conclusion, it can be said that for a species to be allelopathic in nature, it is essential to verify the effect of its possible allelochemicals on the target species, on the soil in which they will exert their action and at the concentrations found in their usual environment, in addition to taking into account the interaction with other compounds present in the medium.

Conyza bonariensis (L.) Cronquist is a widespread noxious weed with high fecundity, associated with no-till systems such as vineyards and other perennial crops in Mediterranean climates. Seeds germinate in staggered flushes, which leads to a great variation in the growth stage between individuals in the same field, and chemical control becomes challenging. Besides, Conyza species have evolved resistance to herbicides worldwide, particularly to glyphosate. Even though tillage is expected to provide weed-free fields, it negatively affects vineyards, causing erosion, loss of soil structure and a reduction in organic matter or vine growth (shallow roots can be affected), among other effects. Fuel consumption of this management is also very high because recurrent interventions of in-row tiller are required. In this context, bioherbicides, defined as environmentally friendly natural substances intended to reduce weed populations, are a potential tool for integrated weed management (IWM). In this work, the herbicidal effect of the following six products is tested on a glyphosate-resistant C. bonariensis population present in commercial vineyards: T1, mixture of acetic acid 20% and the fertilizer N32; T2, mixture of potassium metabisulfite and pelargonic acid 31%; T3, pelargonic acid 68%; T4, humic-fulvic acid 80%; T5, hydroxy phosphate complex; and T6, potassium metabisulfite. The results showed high field efficacy for T1 and T4 (>80% biomass reduction). For the rest of the products, high efficacy was obtained only in dose–response greenhouse experiments. The present work demonstrates the potential of certain bioherbicide compounds to manage herbicide-resistant weed species, such as C. bonariensis. Therefore, bioherbicides could be successfully incorporated into vineyards for IWM.

The productivity of important grain crops wheat, rice and maize is adversely affected by various biotic and abiotic stresses. Weeds and phytopathogens are the major biotic stresses involved in biomass reduction and yield losses of these cereal crops. Various weeds compete with crop plants for natural resources viz. light, moisture, nutrients and space, and cause yield losses to agricultural produce. Weeds also increase harvesting costs and reduce quality of the farm produce. Weed management strategies include crop rotation, mechanical weeding or treatment with different herbicides. Although, sprays of different herbicides control various destructive weeds but their excessive use is environmentally unsafe and uneconomic. Indiscriminate use of these agrochemicals for weed control has resulted into considerable pollution of soil, groundwater and atmosphere. Therefore, effective biological weed management is an attractive approach for achieving the increased crop production to meet the food demands of the escalating global population. Many bacteria and fungi have been identified from the plant rhizospheres, which suppress the growth of weeds. The production of indole acetic acid, aminolevulinic acid, toxins and hydrogen cyanide has been correlated with the growth suppression of various weeds. Interestingly, inoculation with bioherbicides results in creation of biased rhizosphere leading to resource partitioning of nutrients towards growth stimulation of crop plants. Thus, inoculation of plants with bioherbicides has been found to increase germination percentage, seedling vigor, root and shoot growth, seed weight and increased grain, fodder and fruit yields. These environment-friendly biocontrol strategies for management of weeds are highly compatible with the sustainable agriculture.

To help protect the environment as well as increase agricultural production, the use of synthetic herbicides must be reduced and replaced with plant-based bioherbicides. Elaeocarpus floribundus is a perennial, evergreen, and medium-sized plant grown in different areas of the world. The pharmaceutical properties and various uses of Elaeocarpus floribundus have been reported, but its allelopathic potential has not yet been explored. Thus, we carried out the present study to identify allelopathic compounds from Elaeocarpus floribundus. Aqueous MeOH extracts of Elaeocarpus floribundus significantly suppressed the growth of the tested species (cress and barnyard grass) in a dose- and species-dependent way. The three most active allelopathic substances were isolated via chromatographic steps and characterized as (3R)-3-hydroxy-β-ionone, cis-3-hydroxy-α-ionone, and loliolide. All three substances significantly limited the seedling growth of cress, and the compound (3R)-3-hydroxy-β-ionone had stronger allelopathic effects than cis-3-hydroxy-α-ionone and loliolide. The concentrations of the compounds required for 50% growth inhibition (I50 value) of the cress seedlings were in the range of 0.0001–0.0005 M. The findings of this study indicate that all three phytotoxic substances contribute to the phytotoxicity of Elaeocarpus floribundus.

In the face of yield losses caused by weeds, especially in low-input agricultural systems, and environmental pollution due to the excessive use of synthetic herbicides, sustainable weed management has become mandatory. To address these issues, allelopathy, i.e., the biochemical phenomenon of chemical interactions between plants through the release of secondary metabolites into the environment, is gaining popularity. Although many important crops are known for their allelopathic potential, farmers are still reluctant to use such knowledge practically. It is therefore important to assist advisors and farmers in assessing whether allelopathy can be effectively implemented into an eco-friendly weed management strategy. Here, we aim to give a comprehensive and updated review on the herbicidal potential of allelopathy. The major findings are the following: (1) Crops from different botanical families show allelopathic properties and can be cultivated alone or in combination with other non-allelopathic crops. (2) Many allelopathic tools can be adopted (crop rotation, intercropping, cover cropping as living or dead mulches, green manuring, use of allelochemical-based bioherbicides). (3) These methods are highly flexible and feature increased efficiency when combined into an integrated weed management strategy. (4) Recent advances in the chemistry of allelopathy are facilitating the use of allelochemicals for bioherbicide production. (5) Several biotechnologies, such as stress induction and genetic engineering techniques, can enhance the allelopathic potential of crops or introduce allelopathic traits de novo. This review shows how important the role of allelopathy for sustainable weed management is and, at the same time, indicates the need for field experiments, mainly under an integrated approach. Finally, we recommend the combination of transgenic allelopathy with the aforementioned allelopathic tools to increase the weed-suppressive efficacy of allelopathy.

Natural plant resources with herbicidal activity may be substitutes for synthetic chemical pesticides, likewise aromatic plant extracts, especially essential oils. Essential oil from Litsea pungens has been proved to possess a strong antibacterial property. Interestingly, we found the essential oil also showed a strong allelopathic capacity. Therefore, in the present work, the chemical composition of the essential oil from the fruit of L. pungens was analyzed by gas chromatography–mass spectrometry (GC–MS). The weed control abilities of the essential oil were also further evaluated. The results show that the yield of essential oil extracted by steam distillation was 1.4%, and 17 compounds, mainly terpenoids, were identified by GC–MS. In allelopathic tests, the essential oil exhibited a negative effect on seed germination rate and seedling growth of Lolium perenne and Bidenspilosa. Moreover, chlorophyll content, malondialdehyde content, electrolyte leakage, catalase, superoxide dismutase and peroxidase of seedlings treated with essential oil were also negatively affected. This work could provide a better understanding of the rational utilization of L. pungens essential oil for crop cultivation and further development of environment-friendly herbicides.

The sustainable management of weeds is one of the main challenges in agriculture. Recent studies have demonstrated the potential of plant phytotoxins, such as ailanthone from Ailanthus altissima (Mill) Swingle, as bioherbicides. Since a complex extract may be more active than a single compound, we explored the phytotoxicity of A. altissima extracts obtained from the leaves, samaras, rachises, and secondary roots, and we evaluated their application potential for weed control in horticulture. The pre-emergence activity of all plant extracts was evaluated over varying concentrations on two indicator species (i.e., Lepidium sativum L. and Raphanus sativus L.) under controlled conditions. As the leaf extract was able to be generated in sufficient quantities, it was therefore further evaluated in glasshouse experiments with seven common weed species as indicators, as well as in a nursery production system for the cultivation of three horticultural crops (i.e., Salvia officinalis L., S. rosmarinus Schleid., and Dianthus caryophyllus L.). Following the application of the extract, the index of germination (IGe%), the index of biomass, and the density of weeds per pot were evaluated, along with the impact on crop growth and quality (i.e., plant growth index and leaf damage). Under controlled conditions, the extract from the secondary root was the most active in reducing the IGe%, with greater persistence across time in both indicator species. At 18 days following application, the lowest concentration of the leaf extract at 1.8 mg L−1 ailanthone reduced the IGe%by up to 15% and 45% in R. sativus and L. sativum, respectively. In R. sativus, all of the extract types affected the IGe%, but extract activity was greater in L. sativum. Under glasshouse conditions, leaf extracts containing 50 and 200 mg L−1 ailanthone showed strong inhibition (98%–99%) in the biomass of all treated indicator and weed species. Under nursery conditions, leaf extracts formulated at 100 and 200 mg L−1 ailanthone performed similarly, and no weeds were observed in any of the treated pots of S. officinalis and S. rosmarinus in the 60-day study period. Conversely, in the D. caryophyllus pots, an increase in the percentage of weed presence per pot was observed after 40 days. A reduction in the growth index and an increase in leaf phytotoxicity were observed during the cultivation experimentation, especially in S. officinalis when the extract was applied post-emergence to the crop canopy. Phytotoxicity was alleviated by the application of the extract directly to the soil or growth media. These results provide new insights into A. altissima extracts and their phytotoxicity to support their additional use as a sustainable solution for weed management in horticultural crops.

The use of plant water extracts to control weeds is gaining attention in environmentally-friendly agriculture, but the study of the effect that such extracts may exert on the yield of durum wheat is still unexplored. In 2014 and 2016, the herbicidal potential of several plant water extracts was field tested on durum wheat (cv Valbelice). In 2014, extracts obtained from Artemisia arborescens, Rhus coriaria, Lantana camara, Thymus vulgaris, and Euphorbia characias were used, whereas in 2016 only A. arborescens and R. coriaria were tested as “donor” plants. In both years, weed incidence was evaluated, together with the major yield parameters of wheat. None of the treatments (including chemicals) could eradicate weeds from the field. In 2014, dicots were in general prevailing in plots treated with extracts of E. characias, while monocots prevailed after treatments with L. camara and R. coriaria. In 2016, lower weed biomass and diversity level were found, and only Avena and Phalaris were detected at harvest time. Treatment with plant water extracts affected grain yields, but it seems likely that those effects are not due to the diverse incidence of weeds in treated and untreated plots, rather to some direct action exerted by allelopathic substances.

The intensive use of synthetic herbicides is questioned for many reasons. Bioherbicides, as integrated weed management tools, however, have the potential to offer a number of benefits such as increased target specificity and rapid degradation. Despite the efforts to identify effective bioherbicide agents in laboratory and field, only thirteen bioherbicides are currently available on the market. Since 1980, the number of biopesticides has increased around the world, while the market share of bioherbicides represents less than 10% of all biopesticides. Nevertheless, weed management implemented at the cropping systems scale needs bioherbicides because of legislation to drive weed management away from heavy reliance on chemicals, the global increase in organic agriculture, the need of both organic and conventional agriculture to increase weed control efficiency, concerns about herbicide resistance, and concern from the public about environmental safety of herbicides. Consequently, we review here the existing products on the market and describe their history, mode of action, efficacy and target weeds. This review is unique because we also discuss the role of bioherbicides in integrated weed management: to manage soil weed seedbanks with seed-targeted agents in addition to primary tillage, to increase the efficacy of mechanical weeding because bioherbicides are more effective on seedlings, to increase the suppression effect of crop cultivars by first slowing weed growth, to terminate cover crops particularly in conservation agriculture, and finally to manage herbicide resistant populations. [ABSTRACT FROM AUTHOR]

Research about phytotoxic activity of natural compounds could lead both to find new herbicidal active ingredients and to plan environmental friendly weed control strategies. Particularly, living organisms could be a source of compounds that are impossible, for their complexity, to synthesize artificially. More over, they could have alternative sites of action respect to the known chemical herbicides and, due to their origin, they should be more environmental safe. Many living organism, such as bacteria, fungi, insects, lichens and plants, are able to produce bioactive compounds. They generally are secondary metabolites or simply waste molecules. In this paper we make a review about these compounds, highlighting potential and constraints.