Algae Could Be the Next Big Weapon Against Crop Pests and Pathogens

A sweeping review published in Environmental Science and Pollution Research argues that algae, from microscopic cyanobacteria to large seaweeds, could supply the next generation of biopesticides for agriculture. The authors, led by Adegoke Isiaka Adetunji of the Institute for Water and Wastewater Technology at Durban University of Technology, compile evidence that algal metabolites display insecticidal, nematocidal, herbicidal, antibacterial, antifungal, and antiviral activities while remaining biodegradable and largely benign toward beneficial organisms. The review goes beyond cataloguing compounds: it links the chemistry to mechanisms of action, extraction technologies, regulatory hurdles, and, unusually for this field, a techno-economic analysis of what commercial production would actually cost.

The motivation is stark. Synthetic pesticides, including organophosphates, carbamates, organochlorines, and pyrethroids, have long been the default tool for protecting crops, but their overuse carries serious consequences. According to figures cited from the United Nations Environment Programme and the World Health Organization, roughly three million people suffer pesticide poisoning each year and around 200,000 die, particularly in low- and middle-income countries. Chronic exposure has been linked to endocrine disruption, neurotoxicity, type 2 diabetes, cancers, Parkinson’s and Alzheimer’s diseases, infertility, and leukemia. In the environment, residues degrade water quality, kill non-target organisms such as bees and earthworms, damage soil biodiversity, and drive pest resistance, which in turn demands ever-higher doses.

Against this backdrop, the global biopesticide market, valued at 5.75 billion dollars in 2022, is projected to reach 17.57 billion dollars by 2030, growing at roughly 15 percent annually. Algae occupy a distinctive niche within this expansion because they are photosynthetic biofactories that secrete an enormous range of secondary metabolites under stress. The review organizes these into several major classes. Terpenoids, the largest class of natural products with more than 50,000 identified structures, are synthesized in algae via the methylerythritol phosphate pathway in the chloroplast and the mevalonate pathway in the cytosol. Red algae are particularly prolific producers, and sesquiterpenes and monoterpenes from Cladophora and Chaetoceros have shown insect-repellent effects by acting on insect sensory organs.

Alkaloids, nitrogen-rich heterocyclic molecules produced mainly by dinoflagellates and cyanobacteria, induce severe oxidative stress in target pests, generating reactive oxygen species that damage DNA and trigger programmed cell death. Compounds such as 12-epi-hapalindole E isonitrile from Fischerella, calothrixin A from Calothrix, and saxitoxin from diatoms illustrate the chemical arsenal. Phenolic compounds, including phlorotannins and bromophenols abundant in seaweeds, target metabolic enzymes and cell membranes in pathogens while simultaneously priming plant defense pathways. Polyketides, built by polyketide synthases through condensation and reduction reactions, account for roughly a quarter of known bioactive compounds from marine macroalgae and include herbicidal and antifungal agents such as cryptophycins from Nostoc. Peptides, whether assembled by non-ribosomal peptide synthetases or ribosomally and modified afterward, add antimicrobial and nematocidal potency, although their sensitivity to degradation remains a formulation challenge.

The mechanisms of action are genuinely multi-target, which matters because single-site toxicity is what drives rapid resistance in conventional pesticides. Algal compounds disrupt pest neurology and metabolism, destroy microbial cell membranes, inhibit photosynthetic electron transport in weeds, and interfere with quorum sensing, the chemical communication system bacteria use to coordinate infection. Cyanobacterin from cyanobacteria disrupts photosynthetic electron transport in pea chloroplasts, while Fischerellin A from Fischerella muscicola suppresses fungal pathogens including Pyricularia oryzae and Phytophthora infestans. Cyanobacterial metabolites such as microcystin-LR inhibit protein phosphatases PP1 and PP2A, key regulatory enzymes, and anabaenopeptins block zinc-dependent carboxypeptidases. Indirectly, algal polysaccharides elicit systemic plant resistance through jasmonic acid and salicylic acid signaling and strengthen cell walls via the phenylpropanoid pathway.

The biological evidence spans every major pest category. On the antibacterial front, Dunaliella salina hexane extracts rich in beta-carotene reduced disease incidence in Pseudomonas syringae-infected tomato plants by 65.7 percent and severity by 77 percent in in vivo assays, while soft rot symptoms in treated tomato and zucchini fruits fell to 5.3 and 12.6 percent compared with 90.6 and 100 percent in controls. Against fungi, Nostoc ethanolic extracts completely inhibited Sclerotinia sclerotiorum in tomato, and a large screening of 280 microalgal strains found that 45 percent inhibited at least one phytopathogenic fungus or oomycete, with cyanobacteria showing the highest activity at 64 percent. Sulfated polysaccharides such as carrageenans, fucoidans, and ulvans block viral adsorption and entry, protecting plants against cucumber mosaic and tobacco mosaic viruses by eliciting immunity rather than direct toxicity.

Nematode and insect control show equally striking results. Dry powders from the seaweeds Spatoglossum variabile, Stokeyia indica, and Melanothamnus afaqhusainii reduced gall formation and blocked root penetration by the root-knot nematode Meloidogyne incognita in eggplant and watermelon, in some cases matching the commercial nematicide carbofuran. Stoechospermum polypodioides caused nearly 80 percent mortality in Meloidogyne javanica, the highest among 21 species tested. In insects, halogenated monoterpenes from the red alga Plocamium telfairiae killed 80 percent of German cockroaches, and a petroleum ether extract of Nostoc muscorum showed an LC50 of just 155.22 ppm against the devastating fall armyworm Spodoptera frugiperda. As herbicides, the rare sugar 7-deoxysedoheptulose from Synechococcus elongatus blocks the shikimate pathway, the same target as glyphosate, inhibiting cyanobacteria, yeasts, and land plants alike.

What sets this review apart is its willingness to confront the economics. Techno-economic analyses for algal biopesticides are scarce, so the authors built conceptual scenarios for a 1000-liter cultivation system run over ten cycles. A conventional biorefinery using synthetic medium cost 6,792 dollars in operating expenses but generated only about 82 dollars of biopesticide revenue, a clear failure. Replacing 75 percent of the medium with wastewater cut operating costs to roughly 306 dollars while boosting biomass productivity to 2.41 grams per liter, yet a single-product strategy still fell short. Only a multi-product biorefinery, co-extracting pigments, antioxidants, and biopesticides from the same biomass, approached commercial viability, generating over 900 dollars across ten cycles and buffering the economics against yield fluctuations. Earlier work cited in the review supports the concept: Chlorella thermophila grown in dairy wastewater yielded both a biopesticide effective against rice blight pathogens and a 28 percent biocrude oil yield from the residual biomass.

The obstacles to commercialization remain formidable. Large-scale algal cultivation demands enormous quantities of water and nutrients; extraction often relies on expensive technologies and organic solvents; algal extracts can be unstable under field conditions of heat, light, and rain; and their slow, sometimes inconsistent action discourages farmers who need rapid knockdown. Regulatory pathways add another layer of complexity, with the United States Environmental Protection Agency requiring less data under FIFRA than the European Union does under Regulation EC 1107/2009, where biopesticides face data requirements comparable to those for synthetic chemicals. There is no universal regulatory model, and the resulting fragmentation slows global commercialization. The authors also caution that many laboratory results, particularly antibacterial and antiviral findings, rest on in vitro assays with model organisms rather than plant pathogens, and that resistance development in target pests has rarely been systematically tested.

The review’s conclusion is measured rather than triumphal. Algal biopesticides are unlikely to displace established products such as Bacillus thuringiensis or spinosad in the near term; instead, their most realistic role is as complements within integrated pest management, where their multifunctionality, simultaneous pathogen suppression, immune priming, and stress tolerance enhancement, offers the greatest value. The authors call for substantial field trials, CRISPR-based engineering of algal strains to boost specific compounds, nano-formulations to improve stability and targeted delivery, synergistic extract cocktails, and genomic and metabolomic profiling to identify biosynthetic pathways. If those pieces come together, the humble photosynthetic organisms that have thrived in oceans and ponds for billions of years may finally take their place in the farmer’s toolkit, turning wastewater into crop protection and helping agriculture wean itself off its most toxic chemistry.

Subject of Research: Algal bioactive compounds as multi-target biopesticides for sustainable crop protection

Article Title: Algal bioactive compounds for next-generation biopesticides: a multi-target resource for sustainable pest management

Article References: Adetunji, A. I., Ojwach, J. D., Goswami, R. K., Rawat, I., & Bux, F. (2026). Algal bioactive compounds for next-generation biopesticides: a multi-target resource for sustainable pest management. Environmental Science and Pollution Research, 33(30), 15179-15210. https://doi.org/10.1007/s11356-026-38228-3

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38228-3

Keywords: algae, biopesticides, cyanobacteria, seaweeds, sustainable agriculture, crop protection, terpenoids, alkaloids, phenolic compounds, techno-economic analysis, integrated pest management, wastewater cultivation