Strobilurin fungicides are among the most heavily deployed crop protection chemicals in the world. First patented in 1996, azoxystrobin ushered in a family of related compounds — including pyraclostrobin, kresoxim-methyl and trifloxystrobin — that now protect cereals, fruits, vegetables, turf and ornamentals against an unusually broad spectrum of diseases, from downy and powdery mildews to rusts and blights. Their mode of action is precise: the molecules bind to the quinol oxidation site of cytochrome b, a key component of the mitochondrial respiratory chain, effectively shutting down fungal energy production. But because respiration is such a fundamental process, scientists have long worried that the chemicals could disturb non-target organisms, including the bacteria and archaea that drive nutrient cycling beneath our feet.

To probe this question, the team constructed laboratory mesocosms — 2-kilogram portions of each soil — and treated them with Quadris at four concentrations of the active ingredient azoxystrobin: a zero-dose control, 2.90 mg per kg, 14.65 mg per kg and 35.0 mg per kg. The mesocosms were maintained at 60 percent of their maximum water-holding capacity and incubated in darkness at 22 degrees Celsius for 120 days, preventing the breakdown of the fungicide by sunlight. Samples were then pulled at intervals of one, 30, 60, 90 and 120 days, allowing the researchers to track both the chemical fate of the fungicide and the metabolic response of the bacterial communities over time.

The centrepiece of the study was a technique called community-level physiological profiling, performed with Biolog EcoPlates. These microplates contain 31 different carbon sources, which the researchers grouped into five chemical guilds: carbohydrates, polymers, carboxylic acids, amino acids and amines/amides. By measuring how vigorously soil bacteria oxidised each substrate, the team could compute the average well colour development, or AWCD — a proxy for overall catabolic activity — and map the detailed physiological fingerprint of each community. The approach reveals not just how active the bacteria are, but which biochemical menus they prefer.

The results were striking. Across both soil types, Quadris depressed the overall catabolic activity of bacterial communities, and the decline persisted for at least two months before a partial recovery and, in some treatments, a late-stage stimulation by day 120. Notably, the magnitude of the drop in AWCD was largely independent of both soil type and fungicide concentration, suggesting a robust, systemic effect on bacterial metabolism. At the same time, the fungicide consistently suppressed the bacterial utilisation of amines and boosted that of amino acids in both soils, while its effects on carbohydrates, carboxylic acids and polymers depended closely on the specific soil environment and dose applied.

The two soils told clearly different stories about the fungicide’s environmental fate. Azoxystrobin dissipated far more slowly in the clay loam than in the loamy sand: the half-life ranged from 36.5 to 86.6 days in the sandy soil but stretched from 130.8 to 212.1 days in the clay-rich soil, classifying the compound as low to moderately persistent in the former and highly persistent in the latter. The researchers attribute this to differences in texture, pH and organic matter — the loamy sand was moderately acidic at pH 5.63, while the clay loam was near-neutral at 6.99 — which likely govern how bioavailable the chemical is to microorganisms. A more bioavailable fungicide, they reason, degrades faster but also exerts greater toxicity.

The fungicide also disturbed the soils’ chemistry. Applications lowered pH significantly in the loamy sand — by up to 14 percent at the highest dose — a change the authors link partly to the formation of azoxystrobin acid, the major degradation product, and possibly to other ingredients in the commercial formulation. Nitrogen pools shifted as well: nitrate concentrations rose overall in both soils, by as much as 70 percent at the low dose in the clay loam, while ammonium fell by 15 percent in the loamy sand and 39 percent in the clay loam. Because nitrification and mineralisation underpin nutrient turnover, such shifts could, the authors suggest, disrupt soil quality and productivity over the long term.

Perhaps the most subtle insight came from analysing metabolic diversity. Rather than losing the ability to use particular carbon sources outright — a change in

Subject of Research: Non-target effects of the fungicide Quadris (azoxystrobin) on bacterial functional profiles in loamy sand and clay loam soils

Article Title: Differences in bacterial functional profiles from loamy sand and clay loam textured soils under fungicide Quadris R impact

Article References: Petkova, M., Kenarova, A., Boteva, S., Georgieva, S., Chanev, C., & Radeva, G. (2022). Differences in bacterial functional profiles from loamy sand and clay loam textured soils under fungicide QuadrisR impact. BioRisk, 17, 31-43. https://doi.org/10.3897/biorisk.17.76939

Image Credits: AI Generated

DOI: 10.3897/biorisk.17.76939

Keywords: azoxystrobin, strobilurin fungicides, soil bacteria, soil health, CLPP, Biolog EcoPlates, soil microbiology, pesticide non-target effects, nutrient cycling, soil texture, catabolic activity, mesocosm experiment

The core problem identified by author Michal Samek of the Forestry and Game Management Research Institute in the Czech Republic is phenological. Warmer winters and increased early-season humidity have shifted the release of ascospores, the infectious spores of needle cast fungi, to late May or early June. Traditional calendar-based spray schedules, drawn up months in advance on the assumption of predictable pathogen timing, are increasingly out of step with the biology of the organisms they are meant to control. In effect, climate change has broken the synchrony between the forester’s calendar and the fungus’s life cycle, leaving seedlings exposed during precisely the windows when protective residues have worn off.

While the co-application of fungicides and foliar fertilizers is an established paradigm in agricultural crop protection, its transfer to forestry remains largely unexplored. The new communication sets out a theoretical framework for doing exactly that, and it is careful to flag its own epistemic status: the synergistic effects and operational recommendations discussed are literature-supported concepts rather than findings directly validated in the field. Even so, the mechanistic logic is detailed enough to give forest pathologists a concrete set of hypotheses to test, and it rests on two well-characterized modes of action working in parallel.

The first arm of the proposed strategy is azoxystrobin, a member of the quinone outside inhibitor, or QoI, class of fungicides derived from the natural antifungal compound strobilurin. Azoxystrobin suppresses fungal pathogens by inhibiting mitochondrial respiration at the cytochrome bc1 complex, effectively cutting off the energy supply of the pathogen. But the compound does more than kill fungi. In agricultural systems it has been shown to induce secondary physiological responses in the host plant, including delayed senescence of leaves and enhanced nitrogen assimilation. For a recently outplanted pine seedling, whose needles must persist long enough to fuel root establishment, delaying senescence is itself a form of protection.

Equally important is the way azoxystrobin moves through the plant. Following foliar application, the active compound is transported acropetally, meaning upward and outward, via the xylem to developing tissues. This systemic distribution means that new growth emerging after the spray is protected as well, a critical advantage for seedlings that are actively flushing. The fungicide is thus concentrated in aerial tissues, spatially separated from the soil, a detail that turns out to matter enormously for the ecological argument at the heart of the paper.

The second arm of the strategy is the magnesium-hydroxide mineral suspension, and here the physicochemical reasoning becomes particularly technical. Unlike highly soluble inorganic salts, which drastically lower the osmotic potential of the spray solution and can induce acute hyperosmotic stress and localized necrosis on delicate needle tissue, hydroxide-based formulations behave as water-dispersed microparticles. These particles are theorized to alter the viscosity and rheology of the spray, facilitating the formation of a stable, adhesive protective film on the needle epidermis. In effect, the mineral component doubles as a slow-release carrier: it improves the physical persistence of the deposit while gradually supplying magnesium, an essential substrate for photosynthetic activity, to a plant whose metabolism is under siege.

Combined, the two components are hypothesized to yield what the author calls a greening synergy. Azoxystrobin inhibits ethylene biosynthesis, the plant hormone cascade that drives senescence, potentially keeping needles metabolically active for longer. The mineral suspension concurrently supplies the magnesium that sits at the center of every chlorophyll molecule, supporting enhanced photosynthetic efficiency. By delaying needle senescence and stimulating nitrate assimilation, the fungicide could optimize the uptake and incorporation of the magnesium supplied via the foliar suspension, a metabolic priming hypothesized to support the high energy demands of regenerating Pinus tissues under biotic stress. The seedling, in this model, is not merely defended but actively bolstered.

The ecological case for the foliar route rests on what it avoids. Sustainable integrated pest management requires a mechanistic understanding of how external inputs affect the soil ecosystem, and the evidence on conventional approaches is sobering. Chronic application of high-solubility N-P-K fertilizers frequently induces soil acidification, compaction, and hyperosmotic stress, while repeated nitrogen additions have been shown in long-term experiments to decrease forest soil fungal and bacterial biomass. More damaging still, agrochemical soil loading, particularly from certain soil-drenched fungicides, severely disrupts the extraradical mycelium and the functional integrity of common mycorrhizal networks, the underground fungal webs through which forest trees exchange water and nutrients. For a first-year seedling, whose ectomycorrhizal partnerships are essential for optimal water uptake, severing those connections can be as lethal as the pathogen itself.

Because acropetal transport keeps the fungicide concentrated within aerial tissues, the foliar approach is hypothesized to be less disruptive to the rhizosphere than soil drenches, spatially separating the active ingredient from the soil microbiome. The author is careful, however, to frame this as potentially less disruptive rather than definitively protective. Uncertainties remain: foliar wash-off during heavy precipitation could carry residues to the forest floor, and indirect physiological effects on the host plant could still ripple down into the soil community. The claim is one of comparative advantage, not absolute safety, and it is precisely the kind of hypothesis that demands empirical field verification before operational adoption.

The paper is equally candid about the operational and regulatory constraints that stand between concept and practice. The elevated viscosity of a dual-suspension matrix would necessitate continuous mechanical agitation in the tank to prevent particle agglomeration and phase separation. The inclusion of phosphorus-based fertilizers is strictly contraindicated due to antagonistic struvite crystallization, which would lock nutrients into insoluble mineral form. Managers would need to establish optimal dose ranges, spray volume limits, and the rainfastness of the protective film. Most seriously, repeated applications of QoI fungicides exert strong selection pressure that can rapidly induce fungicide resistance in pathogen populations, a risk that has already reshaped agricultural practice worldwide. Strict adherence to regulatory constraints on chemical residues and potential effects on non-target organisms is mandatory.

What emerges is a promising conceptual framework rather than a proven tool, and the author says as much. The synergistic co-application of strobilurin fungicides and mineral foliar suspensions offers a hypothesized pathway for fostering physiological resilience in first-year seedlings, one that could yield both ecophysiological and operational advantages in post-disturbance forest management. If field trials bear out the greening synergy, the reduced soil loading, and the mycorrhizal-sparing profile the model predicts, foresters confronting climate-accelerated needle cast could gain a genuinely dual-action intervention: one that kills the fungus, feeds the tree, and leaves the underground alliance intact. Until then, the tank-mix remains a carefully reasoned bet, awaiting the empirical data that will decide whether it belongs in the sprayer or only in the literature.

Subject of Research: Combined application of strobilurin-based fungicides and foliar fertilizers for integrated pest management in forest seedling protection

Article Title: Synergistic strategies in forest protection: a conceptual perspective on combined application of strobilurin based fungicides and foliar fertilizers

Article References: Samek, M. (2026). Synergistic strategies in forest protection: a conceptual perspective on combined application of strobilurin based fungicides and foliar fertilizers. Discover Ecology, 2(1), Article 27. https://doi.org/10.1007/s44396-026-00043-y

Image Credits: AI Generated

DOI: 10.1007/s44396-026-00043-y

Keywords: azoxystrobin, needle cast, Pinus, integrated pest management, foliar fertilization, magnesium hydroxide, ectomycorrhizal networks, forest pathology, climate change, seedling resilience, tank-mix, QoI fungicides

The study, led by Aline Pompermaier of the Federal University of Fronteira Sul in Brazil with collaborators at Purdue University, focused on a commercial premix fungicide containing two active ingredients: azoxystrobin, a strobilurin compound that blocks mitochondrial respiration in fungi, and tebuconazole, a triazole that inhibits sterol biosynthesis in fungal cell membranes. These dual mechanisms, belonging to Fungicide Resistance Action Committee Groups C3 and G1, make the product highly effective against a broad range of crop diseases, from soybean rust to wheat stripe rust. It is registered for use on more than two dozen crops, including cotton, rice, corn, coffee, sugarcane, and grapes, and is sold in countries including Brazil, Australia, Argentina, Canada, Spain, and Germany.

What makes the new work particularly significant is that the researchers tested the product exactly as it is sold—as a ready-made formulation containing 120 grams per liter of azoxystrobin, 200 grams per liter of tebuconazole, and a substantial fraction of undisclosed excipients. Most previous ecotoxicology studies have either tested single active ingredients or combined pure compounds in the laboratory. Commercial premixes, by contrast, enter waterways as complete formulations, and the inert ingredients they contain can modify how the active substances are absorbed and how toxic they become. The authors argue this distinction matters, and their results suggest it does.

The exposure regime was designed around environmental reality. Zebrafish embryos were placed in solutions containing 30, 100, or 180 micrograms per liter of the fungicide, with concentrations benchmarked against the highest dose of the mixture component, tebuconazole. The two lower levels correspond to tebuconazole concentrations actually measured in surface and groundwaters in Brazil and elsewhere, while the highest matches Brazil’s maximum allowable limit for tebuconazole in drinking water. Notably, all three levels fall well below concentrations of azoxystrobin recorded in some Brazilian agricultural watersheds, where average detections have reached 1,055 micrograms per liter and peaks of 6,672 micrograms per liter—values that dwarf the experimental doses.

Embryos were exposed from 3 to 120 hours post-fertilization, a window covering the critical organogenesis phase when the nervous system, heart, and other organs take shape. The zebrafish is an ideal model for such work: its embryos are transparent, develop externally, and within days display species-specific behaviors that can be quantified with simple video recording. The team monitored 110 embryos per group for survival and hatching, tracked spontaneous movement in 20 embryos per group under a stereomicroscope at 24 hours post-fertilization, and counted heartbeats at 72 hours. Later, they filmed shoaling behavior at five days and tested antipredator responses at seven days using a moving red sphere displayed on a monitor beneath the test plates.

The survival results were stark. Kaplan-Meier analysis revealed that larvae exposed to 100 and 180 micrograms per liter died at significantly higher rates than controls. In the 100 microgram per liter group, the hazard ratio indicated a 70 percent lower probability of survival compared with unexposed animals; at 180 micrograms per liter, survival probability dropped by 63 percent. These are not laboratory extremes—they are concentrations of tebuconazole documented in real waterways and legally permitted in Brazilian tap water. Hatching, remarkably, was unaffected, meaning the fungicide killed embryos after they emerged rather than preventing emergence itself. The authors point out that azoxystrobin, unlike tebuconazole, has no established regulatory limit in drinking water in Brazil, a regulatory gap they describe as a genuine threat to aquatic life.

Equally troubling were the sublethal effects on developing physiology. At the highest concentration, embryos showed significantly reduced spontaneous movement, the early wriggling behavior controlled by the nascent nervous system. Because this reflexive coiling is orchestrated by developing neural circuits, its suppression is widely interpreted as an early warning sign of neurotoxicity or broader developmental impairment. Heart rate told a stranger story: exposure to 30 micrograms per liter slowed larvae heartbeats, while 100 micrograms per liter sped them up. This non-monotonic, potentially biphasic pattern mirrors hormetic responses documented in fish embryos exposed to other contaminants, and the authors caution that the underlying mechanism—whether adaptive compensation, direct cardiotoxicity, or oxidative stress—remains unresolved and warrants dedicated investigation.

The behavioral findings may be the most ecologically provocative. In the shoaling test, larvae exposed to 100 and 180 micrograms per liter bunched significantly closer together than controls, with reduced average distance between individuals. Zebrafish are intensely social animals, and tight shoaling is their primary defense against predators. But abnormally heightened cohesion can signal an anxiety-like state—a baseline perception of danger that persists even when no threat exists. The researchers suggest the exposed larvae behaved as though a predator were always present. Intriguingly, when the team later confronted the animals with an actual simulated threat in the aversive stimulus test, the exposed larvae responded normally, dodging away from the moving sphere just like controls. This dissociation is telling: it indicates the fungicide did not paralyze the animals or destroy their motor capacity, but rather shifted their default behavioral state, plausibly through dysregulation of cholinergic neurotransmitter pathways that govern anxiety and sociability.

The mechanistic picture drawn from prior literature is consistent with this interpretation. Azoxystrobin has been shown to disturb acetylcholinesterase activity, elevate reactive oxygen species, and disrupt dopaminergic signaling in zebrafish brains, while tebuconazole is known to inhibit acetylcholinesterase in larvae, induce oxidative stress in carp and zebrafish, and cause neurochemical and behavioral alterations. A mixture combining a mitochondrial respiratory inhibitor with a sterol biosynthesis inhibitor may therefore impose a dual burden—neural and oxidative—on embryos whose defenses are still under construction, potentially overwhelming redox homeostasis and cardiac regulation simultaneously. The authors are careful to note that they did not measure biochemical biomarkers directly, framing these pathways as plausible hypotheses grounded in the literature rather than confirmed mechanisms, and they call for follow-up work measuring acetylcholinesterase activity, antioxidant enzymes, lipid peroxidation, and gene expression.

The ecological and regulatory implications are difficult to overstate. A fish larva locked in a perpetual state of vigilance burns energy that should fuel growth and reproduction, and an abnormally cohesive shoal may become easier for predators to spot or less efficient at finding food. Reduced larval survival at environmentally realistic concentrations, meanwhile, can ripple through food webs and disrupt trophic cascades. The study’s central message is that environmental risk assessment must evolve beyond testing isolated active ingredients and counting corpses. Sublethal endpoints—heart function, embryonic movement, social behavior—capture harms that mortality statistics miss entirely, and commercially formulated mixtures must be evaluated as the integrated chemical systems they are. As the authors conclude, premix fungicides entering the environment as ready-made cocktails may act additively or synergistically on aquatic fauna, and regulatory frameworks that ignore this reality leave ecosystems—and potentially drinking water supplies—protected by standards built for a simpler chemical age.

Subject of Research: Toxicological effects of a commercial azoxystrobin-tebuconazole fungicide mixture on zebrafish physiology and behavior

Article Title: Beyond mortality: A fungicide mixture alters physiology and causes impaired behavior in zebrafish

Article References: Pompermaier, A., Chagas, F. B., Tamagno, W. A., Galon, L., Hartmann, P. A., & Hartmann, M. (2026). Beyond mortality: A fungicide mixture alters physiology and causes impaired behavior in zebrafish. Ecotoxicology, 35(7), Article 165. https://doi.org/10.1007/s10646-026-03147-z

Image Credits: AI Generated

DOI: 10.1007/s10646-026-03147-z

Keywords: zebrafish, fungicide mixture, azoxystrobin, tebuconazole, ecotoxicology, pesticides, shoaling behavior, developmental toxicity, heart rate, neurotoxicity, water contamination, environmental risk assessment