Agroecological Weed Management and the Potential Role of Fungi-Based Bioherbicides in Conservation: Advantages, Applications and Future Prospects

Abstract

Recently, there has been growing interest by farmers and researchers in various agroecological approaches enhancing biodiversity and conservation including the use of natural herbicides derived from fungi to provide adequate weed control. This change is driven by growing concerns about herbicide resistance, environmental impacts and regulatory requirements. This review summarizes the results of various studies and highlights the efficacy and benefits of fungal bioherbicides in weed control. Fungi-based bioherbicides utilize the natural weed suppression capability of selected fungi to reduce weed density and competitiveness without completely eradicating the plants and such an approach is at the core of agroecology. Bioherbicides contribute to conservation by providing an environmentally friendly alternative to chemical herbicides. By reducing the reliance on synthetic chemicals, fungal bioherbicides help preserve soil health, water quality and protect non-target species, including beneficial organisms such as pollinators and soil microbes. They also promote biodiversity by selectively targeting specific weed species, leaving native plants and other organisms unharmed and favoring diversified weed flora without the dominance of a few species. Despite their promising potential, bioherbicides face several challenges, including delayed action, production difficulties and the potential toxicity of certain fungal toxins to mammals. This review highlights the growing adoption of fungal bioherbicides as an eco-friendly component of Integrated Weed Management (IWM). Further research is necessary to identify optimal fungal strains for controlling persistent weeds without putting at risk the overall biodiversity and to develop improved formulations for enhanced efficacy.

1. Introduction

Weeds are considered a major threat to the sustainability of agriculture as they compete with crops for resources, i.e., light, water and nutrients, affecting crop growth and causing severe yield losses [1,2,3,4]. Oerke [5] estimates the potential losses due to weeds in wheat, maize, rice and cotton at 23%, 40%, 37% and 35% respectively. In recent decades, weed control in agricultural systems has been based on herbicides [6]. Weed control in agriculture has a rich history evolving from early 20th-century methods using inorganic copper salts and sulfuric acid [7]. A pivotal moment in the 1940s saw the commercialization of the first herbicides, 2,4-DB and MCPA [5]. Over the decades, synthetic herbicides have become the cornerstone of weed control in agricultural systems, representing more than 44% of global pesticide sales [8]. Triolet et al. [9] reported a substantial increase in herbicide sales, surging from 20% to 48% between 1960 and 2005. On the other hand, in the last 20 years, no herbicide has been synthesized with a different mode of action than those discovered so far [10].

Even though herbicides are effective in controlling many weeds in the short term, their continuous and repeated use can lead to serious ecological consequences over time [8]. Injury to non-target plants and crops, herbicide residues in water and soil, and human health and environmental concerns are just some of the consequences of herbicides [11]. Another major problem associated with the use of synthetic herbicides is the growing problem of herbicide resistance. Until today, 529 cases of herbicide-resistant weeds have been reported worldwide, against 21 of the 31 known herbicide sites of action and against 168 different herbicides [12]. At the same time, climate change and rising CO₂ affect the efficacy of herbicides on weeds and herbicide use becomes more restricted due to the strict legislation of the European Union (EU), the Green Deal aims to reduce the use and risk of chemical pesticides by 50% by 2030 [8,12,13]. Therefore, there has been an interest in Integrated Weed Management (IWM) and agroecological based approaches to reduce reliance on herbicides and provide more effective weed control.

Due to these challenges, it is crucial to explore additional options for an efficient and agroecological weed management without an “one fits all” approach. Biological control refers to the management of pests, diseases or unwanted species through the use of living organisms, such as predators, parasites or pathogens, to regulate their population and minimize their impact on ecosystems and agriculture [14]. Biological weed control is an alternative option for weed problems and is considered a more environmentally friendly and sustainable approach compared to chemical methods [15]. Evidence showing that biological sources can provide natural products with phytotoxic activity opens a new perspective for weed management [16]. This review aims to explore the potential of fungal bioherbicides within agroecological weed management, their potential synergies with chemical herbicides and their role in supporting conservation efforts by promoting biodiversity and reducing reliance on synthetic chemicals.

2. Bioherbicides

The active ingredients in these formulations are living microorganisms such as bacteria, fungi, as well as their natural by-products and plant-derived inhibitors [9,15]. This review focuses on fungi as the active ingredient in a bioherbicide. Bioherbicides that utilize the weed-suppressing abilities of fungi are called mycoherbicides. These carefully selected fungi suppress weed density, weed biomass and seed production. The plants may not be eliminated, but their competitive ability could be significantly reduced [17]. It is important to point out that bioherbicides are a part of IWM and are not intended to replace chemical herbicides. Bioherbicides are a complementary measure to traditional weed control strategies [15]. Gressel [18] reported that microorganisms, such as fungi, in the soil can significantly enhance the effect of glyphosate. Fungi enhance glyphosate’s effects by weakening plant defenses like phytoalexins and callose production, making the plants more susceptible to fungal infections and allowing the fungi to be more virulent.

There has been a great deal of interest and research into fungi-based bioherbicides for decades. The utilization of plant pathogens for weed control is reported to date back to the early 1900s, with early experiments involving Fusarium oxysporum against Opuntia ficus-indica, and later, in the 1950s, Alternaria cuscutacidae was used to effectively control the persistent parasitic weed Cuscuta spp. [15,19]. The journey of fungal bioherbicides from experimental use to commercial availability is remarkable. Lubao, a bioherbicide containing Colletotrichum gloeosporioides, was first released in China in 1963 to control dodder (Cuscuta spp.) in crops like soybeans. The product became commercially available under the name Lubao in 1987, marking its broader market availability [9]. In 2016, 13 bioherbicides were commercially available worldwide, nine of which were derived from fungal microorganisms [19]. Some of the currently available bioherbicides worldwide are presented in

Table 1. Examples of currently available bioherbicides [8,9,19,20,21,22,23].

Source	Registered Name	Weeds	Country	Released
Fungus Colleotrichum gloeosporioides	Lubao	Cuscuta chinensis	China	1963
Fungus Phytophthora palmivora	DeVine	Morrenia odorata	USA	1981
Fungus Colleotrichum acutatum	Hakatak	Hakea gummosis and H. sericea	South Africa	1990
Fungus Cylindrobasidium leave	Stump out	Poa annua	South Africa	1997
Bacterium Xanthomonas campestris	Camperico	Poa annua	Japan	1997
Fungus Puccinia thalaspeos	Woad Warrior	Isatis tinctoria	USA	2002
Fungus Chondrostereu purpureum	MycoTech/Chontrol/Ecoclear	Woody plants of Rosaceae family	Canada	2004
Fungus Colleotrichum gloeosporioides	Lock Down	Aeschynomene virginica	USA	2006
Fungus Sclerotinia minor	Sarritor	Taraxacum officinale	Canada	2007
Bacterium Streptomyces acidiscabies	Opportune (MBI- 005)	Taraxacum officinale	USA, Japan	2012
Bacterium Gibbago trianthemae	Gibbatrianth	Trianthema portulacastrum	India	2014
Virus Tobamovirus cepa	Solvi Nix	Solanum viarum	USA	2015
Fungus Phoma macrostoma	Biophoma	broad spectrum of broad-leaved weeds	Canada	2016
Fungi Lasiodiplodia pseudotheobromae, Macrophomina phaseolina and Neoscytalidium novaehollandiae	Di-Bak Parkinsonia	Parkinsonia aculeata	Australia	2021
Pine oil + sugar	Bioweed	herbaceous and grass weeds	Australia	Unknown year

.

The mechanisms of action of bioherbicides are not yet fully understood, and research in this area is still developing. However, studies have indicated that many bioherbicides share mechanisms of action similar to those of conventional herbicides. For instance, certain Alternaria species exhibit mechanisms of action comparable to those of triazine herbicides, targeting photosynthesis in weeds [24]. Additionally, bioherbicides often mimic natural plant-pathogen interactions, leveraging processes such as host-specific infection and allelopathy to suppress weed growth [25]. Furthermore, bioherbicides utilize diverse modes of action, including toxin production, disruption of cell membranes and inhibition of vital physiological processes [14,25]. Further research is needed to fully understand the biochemical mechanisms of bioherbicides.

2.1. Advantages of Bioherbicides Based on Fungi

Fungi are a part of microflora and emerge as promising candidates to produce diverse compounds such as toxins, to improve weed control [16]. Furthermore, they can generate or trigger the production of phytotoxic compounds or other metabolites with activity against weeds, insects and other fungal pathogens [24]. Furthermore, fungi stand out in their ease of identification compared to bacteria and viruses, as they have a well-defined taxonomic position and demonstrate high virulence [20].

Unlike chemicals, microbes, particularly those harnessed in bioherbicides like fungi, possess the capacity to adapt to changes in the environment or resistance from a target, thanks to their genetic system [20]. This unique adaptability finds practical application in the evaluation of bioherbicides for controlling persistent weeds, especially in scenarios where conventional herbicides prove ineffective. These include resistant weeds, parasitic weeds, urban weed problems and cases where the aim is to avoid excessive herbicide use, reduce costs and protect the environment [18]. These natural products have advantages such as a shorter half-life of environmental persistence than synthetic herbicides, biodegradability and a reduced likelihood of causing soil and water contamination [24]. Another advantage is that bioherbicides have a high host specificity, so they do not cause problems for non-target plants and the crop. Thus, biodiversity and conservation are protected as the focus is on targeting the most harmful and competitive weed species. It has also been noted that the expense associated with bioherbicides is reported to be less than the commercial cost of corresponding chemical herbicides [26].

Fungal bioherbicides are pathogens that are applied in weeds employing techniques and methodologies similar to those used in the application of conventional herbicides [27]. In addition to conventional methods, another approach to applying bioherbicides is through wound inoculation. This method effectively overcomes several barriers and provides a moist environment, making it particularly useful for tree applications. For smaller weeds, the technique involves mowing the target area and then spraying the bioherbicide, followed by irrigation [28]. Bioherbicides depend on extended durations of high humidity to achieve optimal infection [28].

2.2. Disadvantages of Bioherbicides Based on Fungi

Despite the promising advancements in fungal bioherbicide application techniques, it is crucial to acknowledge the associated drawbacks as shown in Figure 1. The main disadvantages are related to environmental, technical and commercial restrictions. In particular, fungal bioherbicides have a delayed impact depending on environmental conditions. The broad-spectrum efficacy is often a problem for the crop [20]. Technical challenges are intricately linked to the development and large-scale production of bioherbicides. In the realm of commercialization, bio-based innovations encounter a distinct set of challenges. Market competence, patent protection, building consumer confidence and adapting to evolving market dynamics collectively form commercial restrictions [25]. Finally, research has shown that specific fungal pathogens can produce toxins that are harmful to mammals and must be taken into account. For instance, the herbicidal compounds generated by Myrothecium verrucaria are highly effective in weed management. However, this pathogen also produces toxins, such as macrocyclic trichothecenes, which are harmful to mammals [26]. Therefore, in many countries, registration is necessary to ensure that these bioherbicides do not present unacceptable risks to users and the environment, including potential residues in food or feed [29]. Another issue is that in some cases and in agroecosystems with diverse weed populations, the high selectivity of the bioherbicides may be a problem and result in an insufficient control [8]. Addressing these multifaceted obstacles is crucial for the successful integration of innovative technologies and products into the competitive landscape.

2.3. Formulation of Bioherbicides

The formulation of active substances plays a pivotal role in determining the efficiency and overall success of weed control [30]. Pathogens require specific humidity levels (dew periods) and temperatures for fungal spores to successfully germinate, penetrate, infect and ultimately kill their target weeds. The necessary duration for some pathogens may vary from 6 h to over 24 h, depending on the interaction between the pathogen and the host weed [26]. The main role of formulation is to protect the pathogen from environmental factors while promoting disease development. Moreover, the interaction between the pathogenic strains and the formulations has a significant impact on the efficacy of the product [15]. Bioherbicides based on fungi come in two types: liquid and solid formulations [31]. These formulations usually consist of the active component, a mostly inert material and adjuvants. Adjuvants, which may include compounds such as nutrients and/or chemicals, play a critical role in the survival of the pathogen or protect the active ingredient from environmental conditions, and some adjuvants can actively contribute to the infection process of the host [32]. To increase stability and improve spray ability, liquid products are often mixed with diluents and surfactants [27]. In the commercial market, the preference is for liquid formulations where the majority of bioherbicide formulations are in a liquid state. Under optimum conditions, liquid formulations have the potential to cause infection shortly after application [20]. This emphasis on liquid formulations underlines their practical advantages and their dominance in bioherbicide production.

Strategic delivery of pathogens that target below or at the soil surface through solid or granular formulations as pre-plant or pre-emergence products is suggested by Boyette et al. [27]. This approach offers several advantages, such as acting as a buffer against environmental conditions, serving as a nutrient source for the fungus, leading to prolonged persistence and reducing the likelihood of being washed away compared to spores. Solid formulations can utilize various materials like corn, vermiculite, sodium alginate, kaolin clay and semolina wheat for effective application [27,33].

2.4. Selectivity

Bioproducts derived from plant pathogens tend to have higher selectivity compared to synthetic chemicals, probably because they are derived from specific weed hosts [34]. Evidence of that is a study on the selectivity of bioherbicides by Junior et al. [35], in which Trichoderma koningiopsis caused up to 60% of foliar damage to Euphorbia heterophylla, while it showed no phytotoxicity on maize and only 15% on soybean. Such selective bioherbicides are invaluable for the management of agroecosystems as they focus on specific weed species, thereby protecting crops, increasing yields and contributing to sustainable farming practices. While recent findings by Dubovik et al. [36] and Triolet et al. [9] suggest that selectivity profiles may vary due to added adjuvants and secondary metabolites may affect a broader range of hosts, these findings provide important information for refining and improving the development of fungi-based herbicides.

In order to identify the selectivity of a fungal bioherbicide, a host range test was performed, utilizing plant species, including weeds, vegetables and field, to evaluate and define the host range of a fungus or a second metabolite. Adetunji et al. [37] found that a strain of Pseudomonas aeruginosa showed insignificant levels of phytotoxicity to tested crops such as sorghum, oat and rice but was highly phytotoxic on Amaranthus hybridus. Research has also shown that non-selective phytotoxic activity can vary significantly depending on the plant species. For example, in an experiment investigating the herbicidal effect of Stagonospora cirsii on plants from different families, it was found that all 18 plant species were affected. However, wheat, couch-grass and cucumber were significantly more sensitive compared to the other species [36]. Another study on Colletotrichum coccodes revealed that it can target Abutilon theophrasti without affecting closely related species like cotton [38].

3. Effects of Fungi-Based Herbicides on Weeds

Several studies indicating the biological value of phytopathogenic fungi around the world demonstrated the feasibility of such approaches in agriculture. One notable research by Boyette et al. [39] explored the effect of different concentrations of a mycelial formulation of Myrothecium verrucaria to effectively control Sesbania exaltata at different growth stages in rice under field conditions. The results showed that the formulation with the maximum mycelium concentration and a surfactant reduced the weed biomass at the 10–20 cm growth stage by 95%. At the same time, rice yields in the plots with the bioherbicide treatment at the maximum rate were similar to the yields of the plots treated with a post-emergence herbicide. Similarly, in maize, a bioherbicide formulated with pasta granules based on Lasiodiplodia pseudotheobromae exhibited positive effects on plant growth components compared to the herbicide treatment. In terms of weeds, the bioherbicide achieved an efficiency control of 72% [40].

Seeds of Lolium multiflorum and Sorghum halepense showed no root sprouts after the application of fermented broth containing secondary metabolites of Diaporthe sp. used as pre-emergence. The shoot dry biomass of Conyza sp. treated with the same formulation as post-emergence was reduced by 50% compared to the untreated control [41]. There is also evidence that spores of Colletotrichum coccodes applied in water in combination with a surfactant achieved 95% mortality of Solanum ptycanthum after 16 h of dew, in a greenhouse experiment [42]. There is also evidence that bioherbicides could control underground plant organs. Kadir et al. [43] observed that Dactylaria higginsii at a dose of 106 conidia/ml caused a significant reduction in dry weight of shoots and tubers of Cyperus rotundus by 71% and 67%, respectively, compared to the control. According to Lee et al. [44] Myrothecium roridum showed 100% control of weeds such as Xanthium strumarium, Abutilon avicennae, Digitaria sanguinalis and Echinochloa crus-galli. It is noteworthy that no herbicidal effect was observed against Oryza sativa. These results indicate the potential use of M. roridum as a selective bioherbicide for rice weed control.

Recent studies have shown that Macrophomina phaseolina do not affect several important crops. In particular, the above-mentioned fungus showed a reduction in root dry weight of up to 80% in Convolvulus arvensis. At the same time, no inhibitory effects were observed on chickpea, bean, sorghum, maize or tomato plants [45]. In addition, studies involving Convolvulus arvensis treated with the fungus Phomopsis convolvulus showed a reduction in biomass of up to 100% and 98% in both seedlings and established plants, respectively [46].

A study demonstrated that isolates of Phoma multirostrata effectively controlled Tridax procumbens, achieving disease incidence rates of 60–100% within 2–3 weeks [47]. In another study focusing on Xanthium strumarium, a comparison was made between a conidial suppression formulation and both liquid and solid formulations using Alternaria alternata fungi. The results revealed the superior herbicidal effect of the liquid formulation, which achieved a significant reduction in height, root length and dry weight of Xanthium strumarium by up to 50%, 27% and 58%, respectively, in pot trials [48]. A similar study by Xiao et al. [49] has estimated that Bipolaris bicolor resulted in a disease index of 99 and 98 in Eleusine indica and Setaria viridis, respectively, while proving safe for 14 out of 17 crop species. Notably, among the unaffected crops were cotton, rice, tea and tomato. Additionally, Trichoderma polysporum significantly reduced the weight of Elsholtzia densa, Polygonum lapathifolium and Chenopodium album by 91%, 89% and 88%, respectively, compared to the untreated control [50] (

Table 2. Indicative effects of potential fungal bioherbicides on weeds.

Fungi	Effect on Weeds	Reference
Myrothecium verrucaria	Reduction of Sesbania exaltata biomass by 95%	[39]
Lasiodiplodia pseudotheobromae	Reduction of annual weeds by 72%	[40]
Diaporthe sp.	Root sprouting prevention of Lolium multiflorum and Sorghum halepense	[41]
	Reduction of Conyza sp. shoot dry biomass by 50%
Colletotrichum coccodes	95% mortality of Solanum ptycanthum	[42]
Dactylaria higginsii	Reduction in shoot and tuber dry weights of Cyperus rotundus by 71% and 67%, respectively	[43]
Myrothecium roridum	100% control of Xanthium strumarium, Abutilon avicennae, Digitaria sanguinalis and Echinochloa crus-galli	[44]
Macrophomina phaseolina and Alternaria alternata	Reduction of Convolvulus arvensis root dry weight by up to 80%	[45]
Phomopsis convolvulus	Biomass reduction of Convolvulus arvensis up to 98–100%	[46]
Phoma multirostrata	Control of Tridax procumbens	[47]
Alternaria alternata	Reduction of Xanthium strumarium dry weight by 58%	[48]
Bipolaris bicolor	Control of Eleusine indica and Setaria viridis	[49]
Trichoderma polysporum	Reduction of Elsholtzia densa, Polygonum lapathifolium and Chenopodium album weight by 91%, 89% and 88%, respectively	[50]

).

Effects of Fungal Bioherbicides in Combination with Herbicides

Plants utilize diverse physical and biochemical mechanisms to resist pathogen infections. Certain chemicals, including herbicides, plant growth regulators and specific enzyme inhibitors, have the ability to undermine these defense mechanisms [51]. Although mycoherbicides show promise in weed management, there is evidence suggesting that fungal bioherbicides can synergize with traditional herbicides, leading to more effective results. In synergy trials, the combined application of Myrothecium verrucaria with glyphosate at minimum rates demonstrated remarkable efficacy, achieving 70% control of kudzu weed (Pueraria lobata), in a field experiment. Remarkably, glyphosate alone, when applied at the same minimum rate, provided 10% efficacy against kudzu, while Myrothecium verrucaria spores in isolation exhibited 15% control of the same weed [52]. Another study showed that Myrothecium verrucaria had an herbicidal activity against glyphosate-resistant Amaranthus palmeri. M. verrucaria reduced by 50% the weight of resistant plants, while glyphosate caused no damage. The combination of M. verrucaria and glyphosate leads to a substantial reduction in plant weight by 90% [53]. The combined application of glyphosate and M. verrucaria demonstrated synergistic effects. However, it is important to highlight that not all commercially available products were found to be compatible with M. verrucaria [54].

Diverse studies involving various fungi showcase a broad spectrum of potential applications, shedding light on the multifaceted landscape of integrated weed management strategies. Mitchell et al. [55] demonstrated synergy between glyphosate and two potential bioherbicides, for the control of Sorghum bicolor. Treatments of glyphosate applied either 1 or 3 days before the fungus Colletotrichum graminicola or Gloeocercospora sorghi showed 100% control of the weed. Specifically, the treatment of glyphosate applied before the Colletotrichum graminicola or Gloeocercospora sorghi increased the biomass loss by 47% and 40%, respectively, compared to glyphosate application alone. Recent research has established that the association of synthetic herbicides with mycoherbicides is promising for reducing the required amounts of synthetic herbicides. Different commercial products of glyphosate associated with Trichoderma koningiopsis bioherbicide controlled Euphorbia heterophylla plant from the lowest concentration that caused 80–90% of plant control [56]. The widespread use of various biological products alongside glyphosate is due to its comprehensive efficiency in controlling weeds [56].

Several studies have been also conducted with other chemicals. For instance, a study by Graham [57] assessed the association of various herbicides with the fungus Colletotrichum truncatum. The most effective combination provided effective chamomile control was clopyralid plus MCPA ester and metribuzin applied with the fungus. A similar study examined the application of toxins or fungal spores, together with low doses of herbicides to control the noxious weed Chenopodium album [58]. The results showed that metribuzin applied alone caused around 70% reduction and the combined treatment with the toxins of fungus Ascochyta caulina and the lower dose of metribuzin herbicide caused more than 90% reduction of fresh weight of the weed. Boyette et al. [59] found that the application of Fusarium lateritium 5 min after that of 2,4-DB herbicide decreased the biomass of Abutilon theophrasti by 67% compared to the herbicide treatment alone (

Table 3. The combination of synthetic herbicides and potential fungal bioherbicides for effective weed control.

Fungi	Herbicide	Weed	Reference
Myrothecium verrucaria	glyphosate	Pueraria lobata, Amaranthus palmeri	[52,53]
Colletotrichum graminicola	glyphosate	Sorghum bicolor	[55]
Gloeocercospora sorghi	glyphosate	Sorghum bicolor	[55]
Trichoderma koningiopsis	glyphosate	Euphorbia heterophylla	[56]
Colletotrichum truncatum	clopyralid plus MCPA ester and metribuzin	Matricaria perforata	[57]
Ascochyta caulina	metribuzin	Chenopodium album	[58]
Fusarium lateritium	2,4-DB	Abutilon theophrast	[59]

).

These results underline the synergistic effects observed when fungi are combined with herbicides and highlight its potential as an effective weed management. Necessary to identify compatible herbicides and commercial products with mycoherbicides as the co-formulants in each formulation also play an important role [53,55].

4. Current Status of Fungal Bioherbicides in Weed Management

This section explores the potential role of fungi as bioherbicides in weed management through a systematic review of the literature. Our systematic literature review conducted in the Scopus database covered the period from 2000 to 2024. The search criteria included articles from the past 24 years using the terms (TITLE-ABS-KEY (“bioherbicides”) AND TITLE-ABS-KEY (“fungi”). Language was restricted to English and review articles were excluded. Through this research, we identified 136 articles, with the number of publications showing an increasing trend over the years (Figure 2).

The increasing number of publications on fungi bioherbicides can be attributed to increased environmental concerns, stricter regulatory frameworks and the demand for sustainable and effective alternatives to chemical herbicides [11,12]. Additionally, the growing market potential and enhanced funding for eco-friendly agricultural solutions further fuel this rising interest and research output. Reflecting this shift, Fusarium sp., Trichoderma sp. and Alternaria sp. have emerged as the most extensively studied fungi species in bioherbicide research from 2020 to 2024, highlighting their potential role in advancing sustainable weed management strategies (

Table 4. Fungi most studied as potential bioherbicides from 2020 to 2024 (indexed in the Scopus database).

Fungi	Weed	Reference
Alternaria sp.	Alternathera philoxeroides	[60]
Alternaria sp.	Rumex dentatus, Sonchus oleraceus, Avena fatua, Polypogon monspeliensis, Setaria viridis, Echinochloa crus-galli, E. colona and Plantago major	[61]
Aspergillus sp.	Ageratina adenophora	[62]
Bipolaris sp.	Eleusine indica	[49]
Bipolaris sp.	Microstegium vimineum	[63]
Diaporthe sp.	Bidens pilosa, Amaranthus viridis, Echinochloa crus-galli. and Lolium multiflorum	[64]
Emericellopsis sp.	Amaranthus retroflexus	[65]
Fusarium sp.	Pontederia crassipes	[66]
Fusarium sp.	Brassica rapa	[67]
Lasiodiplodia sp.	Amaranthus hybridus and Echinochloa crus-galli	[68]
Lasiodiplodia sp.	Chromolaena odorata and Echinocholoa crus-galli	[69]
Penicillium sp.	Ageratina adenophora	[62]
Penicillium sp.	Amaranthus retroflexus	[70]

).

Mohammed et al. [61] examined the potential of two Alternaria species, a Nigrospora species and a Chaetomium species, as bioherbicides against various weeds. Although Alternaria sp. is one of the most studied fungi, it did not provide the best weed control; the Nigrospora fungus was more effective. Citrinin, a bioactive compound produced by the fungi Penicillium and Aspergillus showed promising results, causing phytotoxicity in 20 of 24 weeds studies with leaf lesion areas ranging from 10 to over 40 mm² [62]. In addition, research has shown that other compounds of Penicillium have a phytotoxic effect on several weeds [70]. Another study found that the fungus Bipolaris bicolor is an excellent candidate for a bioherbicide against gramineous weeds as it did not affect weeds from the families Convolvulaceae, Amaranthaceae, Compositae and Leguminosae [50]. This was also confirmed by Tan et al. [63], who found that 20 graminaceous weeds were extremely sensitive, while 77 crop species from 27 plant families were unaffected.

Fusarium sp. is another extensively researched fungus. Fusarium oxysporum and F. equiseti are considered bioherbicides with limited potential as they are pathogenic to many economically important crops. However, specialized biotypes of Fusarium are highly host-specific [68]. Adetunji et al. [69,70] observed that random mutagenesis and the influence of C:N ratio enhanced the bioherbicidal activities of phytotoxic metabolites of Lasiodiplodia sp.

The trend in recent years indicates that researchers are increasingly recognizing the potential efficacy of fungal herbicides. This recognition has led to an increasing focus on conducting larger scale experiments with fungal bioherbicides to evaluate their effects on a wider range of weed species. These efforts are likely due to the increasing demand for environmentally friendly methods of weed control. It also appears that researchers are shifting their focus towards to improving the efficacy of fungal bioherbicides.

5. Conclusions

Fungi-derived bioherbicides can significantly contribute to agroecological weed management and be effectively incorporated into Integrated Weed Management programs, where they complement chemical herbicides to control challenging weeds. At the same time, the high selectivity of such agents can focus only on the most harmful weeds without jeopardizing biodiversity and conservation. Fungal-based bioherbicides have proven effective both alone and in combination with chemical herbicides, demonstrating high selectivity without harming crops. Although this technology is very promising and rapidly developing, optimization by means of systematic and extended research is certainly required. This includes improving commercialization, addressing regulatory issues, discovering suitable fungal sources and understanding the modes of action of each bioherbicide class. Identifying and selecting fungal strains with high efficacy and adaptability to various environmental conditions, including temperature, humidity and soil type, is crucial. Strain enhancement through genetic or metabolic engineering could improve resilience and performance. Extensive field trials under diverse conditions will assess bioherbicides’ performance and environmental impact, allowing for adjustments to enhance efficacy and safety. However, the combination of chemical herbicides with bioherbicides also poses certain risks that must be carefully addressed. Toxicity accumulation, resulting from the combined use of herbicides and bioherbicides, may lead to the buildup of toxic residues in soil and water, posing risks to non-target organisms and potentially contaminating ecosystems. The ecological impact of synergistic combinations may disrupt soil microbiota, reducing biodiversity or harming beneficial microbes critical for plant and soil health. Further research into the interactions between fungi and herbicides could increase the efficacy of fungal-herbicide combinations and thus benefit the conservation and diversity of the non-harmful spontaneous vegetation and reduce the amounts of herbicide and fungal concentrations required for weed control.